MODELS and ASSIMILATION

Adams, J. L., D. J. Stensrud, 2005: Impact of tropical easterly waves on gulf surges during the North American Monsoon. Sixth Conference on Coastal Meteorology, San Diego, CA, USA, American Meteorological Society, 5.7.

Adams, J. L., D. J. Stensrud, 2007: Impact of tropical easterly waves on the North American monsoon. Journal of Climate, 20, 1219-1238.

The North American monsoon (NAM) is a prominent summertime feature over northwestern Mexico and the southwestern United States. It is characterized by a distinct shift in midlevel winds from westerly to easterly as well as a sharp, marked increase in rainfall. This maximum in rainfall accounts for 60%–80% of the annual precipitation in northwestern Mexico and nearly 40% of the yearly rainfall over the southwestern United States. Gulf surges, or coastally trapped disturbances that occur over the Gulf of California, are important mechanisms in supplying the necessary moisture for the monsoon and are hypothesized in previous studies to be initiated by the passage of a tropical easterly wave (TEW). Since the actual number of TEWs varies from year to year, it is possible that TEWs are responsible for producing some of the interannual variability in the moisture flux and rainfall seen in the NAM.

To explore the impact of TEWs on the NAM, four 1-month periods are chosen for study that represent a reasonable variability in TEW activity. Two continuous month-long simulations are produced for each of the selected months using the Pennsylvania State University–National Center for Atmospheric Research Mesoscale Model. One simulation is a control run that uses the complete boundary condition data, whereas a harmonic analysis is used to remove TEWs with periods of approximately 3.5 to 7.5 days from the model boundary conditions in the second simulation. These simulations with and without TEWs in the boundary conditions are compared to determine the impact of the waves on the NAM. Fields such as meridional moisture flux, rainfall totals, and surge occurrences are examined to define similarities and differences between the model runs. Results suggest that the removal of TEWs not only reduces the strength of gulf surges, but also rearranges rainfall over the monsoon region. Results further suggest that TEWs influence rainfall over the Southern Plains of the United States, with TEWs leading to less rainfall in this region. While these results are only suggestive, since rainfall is the most difficult model forecast parameter, it may be that TEWs alone can explain part of the inverse relationship between NAM and Southern Plains rainfall.

Anabor, V., D. J. Stensrud, O. L. L. De Moraes, 2008: Serial upstream-propagating mesoscale convective system events over southeastern South America. Monthly Weather Review, 136, 3087-3105.

Serial mesoscale convective system (MCS) events with lifetimes over 18 h and up to nearly 70 h are routinely observed over southeastern South America from infrared satellite imagery during the spring and summer. These events begin over the southern La Plata River basin, with individual convective systems generally moving eastward with the cloud-layer mean wind. However, an important and common subset of these serial MCS events shows individual MCSs moving to the east or southeast, yet the region of convective development as a whole shifts upstream to the north or northwest. Analyses of the composite mean environments from 10 of these upstream-propagating serial MCS events using NCEP/NCAR reanalysis data events indicates that the synoptic conditions resemble those found in mesoscale convective complex environments over the United States. The serial MCS events form within an environment of strong low-level warm advection and strong moisture advection between the surface and 700 hPa from the Amazon region southward. One feature that appears to particularly influence the low-level flow pattern at early times is a strong surface anticyclone located just off the coast of Brazil. At upper-levels, the MCSs develop on the anticyclonic side of the entrance region to an upper-level jet. Mean soundings show that the atmosphere is moist from the surface to near 500 hPa, with values of convective available potential energy above 1200 J kg-1 at the time of system initiation. System dissipation and continued upstream propagation to the north and northwest occurs in tandem with a surface high pressure system that crosses the Andes Mountains from the west.

Biggerstaff, M., L. Wicker, J. Guynes, C. Ziegler, J. Straka, E. Rasmussen, A. Doggett IV, L. Carey, J. Schroeder, C. Weiss, 2005: The Shared Mobile Atmospheric Research and Teaching Radar: A collaboration to enhance research and teaching. Bulletin of the American Meteorological Society, 86, .

Biggerstaff, M. I., D. R. MacGorman, W. D. Rust, C. Ziegler, J. M. Straka, T. J. Schuur, G. Carrie, K. Kuhlman, E. Rasmussen, P. Krehbiel, W. Rison, T. Hamlin, 2005: The role of storm dynamics on cloud electrification: The 29 May 2004 Tornadic Supercell Observed During TELEX. Preprints, 32nd Conference on Radar Meteorology, Albuquerque, NM, USA, American Meteorological Society, CD-ROM, 15R.1.

Biggerstaff, M. I., D. W. Burgess, G. D. Carrie, E. R. Mansell, L. J. Wicker, C. L. Ziegler, 2008: Storm-Scale Sampling Strategies for the Mobile C-Band Doppler Radars during VORTEX2. Extended Abstracts, 24th Conference on Severe Local Storms, Savannah, GA, USA, American Meteorological Society, 5.2.

Brown, R. A., B. A. Flickinger, E. Forren, D. M. Schultz, D. Sirmans, P. L. Spencer, V. T. Wood, C. L. Ziegler, 2005: Improved detection of severe storms using experimental fine-resolution WSR-88D measurements. Weather and Forecasting, 20, 3-14.

NSSL Outstanding Scientific Paper Award

Doppler velocity and reflectivity measurements from WSR-88D (Weather Surveillance Radar - 1988 Doppler) radars provide important input to forecasters as they prepare to issue short-term severe storm and tornado warnings. Current-resolution data collected by the radars have an azimuthal spacing of 1.0° and range spacing of 1.0 km for reflectivity and 0.25 km for Doppler velocity and spectrum width. To test the feasibility of improving data resolution, National Severe Storms Laboratory's test-bed WSR-88D (KOUN) collected data in severe thunderstorms using 0.5° azimuthal spacing and 0.25 km range spacing,resulting in eight times the resolution for reflectivity and twice the resolution for Doppler velocity and spectrum width. Displays of current-resolution WSR-88D Doppler velocity and reflectivity signatures in severe storms were compared with displays showing finer-resolution signatures. At all ranges, fine-resolution data provided better depiction of severe storm characteristics. Eighty-five percent of mean rotational velocities derived from fine-resolution mesocyclone signatures were stronger than velocities derived from current-resolution signatures. Likewise, about 85% of Doppler velocity differences across tornado and tornadic vortex signatures were stronger than values derived from current-resolution data. In addition, low-altitude boundaries were more readily detected using fine-resolution reflectivity data. At ranges greater than 100 km, fine-resolution reflectivity displays revealed severe storm signatures, such as bounded weak echo regions and hook echoes, which were not readily apparent on current-resolution displays. Thus, the primary advantage of fine-resolution measurements over current-resolution measurements is the ability to detect stronger reflectivity and Doppler velocity signatures at greater ranges from a WSR-88D.

Brown, R. A., J. M. Lewis, 2005: Path to NEXRAD: Doppler radar development at the National Severe Storms Laboratory. Bulletin of the American Meteorological Society, 86, 1459-1470.

In this historical paper, we trace the scientific- and engineering-based steps at the National Severe Storms Laboratory (NSSL) and in the larger weather radar community that led to the development of NSSL's first 10-cm wavelength pulsed Doppler radar. This radar was the prototype for the current NEXRAD (NEXt generation weather RADar) or WSR-88D (Weather Surveillance Radar-1988 Doppler) Network.

We track events, both political and scientific, that led to the establishment of NSSL in 1964. The vision of NSSL's first director, Edwin Kessler, is reconstructed through access to historical documents and oral history. This vision included the development of Doppler radar where research was to be meshed with the operational needs of the U.S. Weather Bureau and its successor the National Weather Service.

Realization of the vision came through steps that were often fitful, where complications arose due to personnel concerns, and where there were always financial concerns. The historical research indicates that: (1) the engineering prowess and mentorship of Roger Lhermitte was at the heart of Doppler radar development at NSSL; (2) key decisions by Kessler in the wake of Lhermitte's sudden departure in 1967 proved crucial to the ultimate success of the project; (3) research results indicated that Doppler velocity signatures of mesocyclones are a precursor of damaging thunderstorms and tornadoes; and (4) results from field testing of the Doppler-derived products during the 1977-1979 Joint Doppler Operational Project -- especially the noticeable increase in the verification of tornado warnings and an associated marked decrease in false alarms -- led to the government decision to establish the NEXRAD network.

Buban, M. S., C. L. Ziegler, E. N. Rasmussen, Y. P. Richardson, 2007: The Dryline on 22 May 2002 during IHOP: Ground-Radar and In Situ Data Analyses of the Dryline and Boundary Layer Evolution. Monthly Weather Review, 135, 2473-2505.

On the afternoon and evening of 22 May 2002, high-resolution observations of the boundary layer (BL) and a dryline were obtained in the eastern Oklahoma and Texas panhandles during the International H2O Project. Using overdetermined multiple-Doppler radar syntheses in concert with a Lagrangian analysis of water vapor and temperature fields, the 3D kinematic and thermodynamic structure of the dryline and surrounding BL have been analyzed over a nearly 2-h period. The dryline is resolved as a strong (2–4 g/kg/km) gradient of water vapor mixing ratio that resides in a nearly north–south-oriented zone of convergence. Maintained through frontogenesis, the dryline is also located within a gradient of virtual potential temperature, which induces a persistent, solenoidally forced secondary circulation. Initially quasi-stationary, the dryline retrogrades to the west during early evening and displays complicated substructures including small wavelike perturbations that travel from south to north at nearly the speed of the mean BL flow. A second, minor dryline has similar characteristics to the first, but has weaker gradients and circulations. The BL adjacent to the dryline exhibits complicated structures, consisting of combinations of open cells, horizontal convective rolls, and transverse rolls. Strong convergence and vertical motion at the dryline act to lift moisture, and high-based cumulus clouds are observed in the analysis domain. Although the top of the analysis domain is below the lifted condensation level height, vertical extrapolation of the moisture fields generally agrees with cloud locations. Mesoscale vortices that move along the dryline induce a transient eastward dryline motion due to the eastward advection of dry air following misocyclone passage. Refractivity-based moisture and differential reflectivity analyses are used to help interpret the Lagrangian analyses.

Buban, M., C. L. Ziegler, E. N. Rasmussen, Y. Richardson, 2005: The structure and evolution of the dryline and surrounding boundary layer on 22 May 2002 during IHOP. Preprints, 11th Conference on Mesoscale Processes, Albuquerque, NM, USA, AMS, J6J.3.

Buban, M., C. Ziegler, Y. Richardson, 2008: Numerical simulations of the dryline and surrounding boundary layer on 22 May 2002 during IHOP. Extended Abstracts, 24th Conference on Severe Local Storms, Savannah, GA, USA, AMS, 18.4.

On the afternoon and evening of 22 May 2002, high-resolution data of the dryline and surrounding boundary layer (BL) were collected in the Oklahoma and Texas panhandles as part of the International H2O Project. Using over-determined multiple Doppler radar syntheses in concert with an innovative Lagrangian analysis technique, the 3-D kinematic and thermodynamic structure of the dryline and surrounding BL have been obtained over nearly a 2-hour period. A past study utilizing these analysis tools has delineated the 22 May dryline as a strong gradient of water vapor mixing ratio embedded in a zone of multi-Doppler radar-derived convergence. Misocyclones are observed to propagate from south to north along the dryline. The BL on both sides of the dryline exhibits complicated structures such as horizontal convective rolls, transverse rolls, and open convective cells.

In the present study, the time-varying radar and Lagrangian analyses have been used as initial and time-dependent lateral inflow boundary conditions to run high-resolution simulations of the dryline and BL. Simulations are conducted with the COllaborative Model for Multiscale Atmospheric Simulation (COMMAS), a 3-dimensional non-hydrostatic community cloud model which includes both short- and long-wave radiation, a force-restore surface physics parameterization, and a cloud microphysics parameterization. The simulations reproduce a nearly north-south oriented dryline with horizontal moisture and temperature gradients similar to observed values, as well as misocyclones, horizontal convective rolls, transverse rolls, and open convective cells. These simulated BL features are similar to analogous structures manifested in the observations and the Lagrangian analyses, although the modeled features are typically of higher spatial and temporal resolutions and may have larger amplitudes than the equivalent observed features. The simulated BL features are internally consistent with the model dynamics, with the high spatial and temporal resolution potentially permitting a better understanding of their evolution processes.

A feature of special interest are the misocyclones which develop and propagate northward along the dryline. Apparently forced in the simulations via longer wavelength undulations in the momentum and thermodynamic fields that are introduced at the lateral inflow boundaries, these perturbations collapse in scale and amplify into intense misovortices as they move downstream. The misocyclones act to modulate the moisture fields along the dryline, bringing larger moisture values westward ahead of and drier air eastward behind the misocyclone relative to its motion. The vertical motion within the deeper moist layer north of the misocyclone enhances simulated cumulus formation along and north of the axis of rotation.

The model simulations are compared to observations to qualitatively evaluate the strengths and weaknesses of the Lagrangian analyses. Aspects of the dryline circulation and other BL features are discussed along with their potential role in the convection initiation process.

Cohen, A. E., M. C. Coniglio, S. F. Corfidi, S. J. Corfidi, 2006: Discrimination among non-severe, severe, and derecho-producing mesoscale convective system environments. Extended Abstracts, Severe Local Storms Symposium, 86th Amer. Meteor. Soc. Annual Meeting, Atlanta, GA, USA, American Meteorological Society, CD-ROM, P1.15. [Available from National Weather Center, 120 David L. Boren Blvd, Norman, OK, USA, 73071.]

Available online at ://http://ams.confex.com/ams/pdfpapers/103614.pdf.

Cohen, A. E., E. R. Mansell, 2008: Flash rate, electrical, microphysical, and dynamical relationships across a simulated storm spectrum. Extended Abstracts, Third Conference on Meteorological Applications of Lightning Data, New Orleans, LA, USA, American Meteorological Society, 4.5.

Many studies have suggested relationships between intracloud and cloud-to-ground flash rates and microphyiscal variables both from an observational perspective and for specific storm intensity and morphology. These relationships provide a necessary component to lightning forecasting, especially when combined with improved and more comprehensive radar data. This study provides an analysis of the relationships between flash rates and several microphysical quantities across a wide spectrum of simulated storms. Some of these quantities include electric field, graupel volume, updraft mass flux, rain mass, ice crystal mass flux, updraft volume, maximum updraft, and cloud ice mass. Eleven unique storms were simulated using the Collaborative Model for Multiscale Atmospheric Simulation (COMMAS) to maximize the temporal and spatial resolution of the analysis. Modifications to surface moisture and bulk shear depth and magnitude yielded a wide range of storm intensity and morphology, from weak, unicell storms, to strong squall lines and supercells. Each case was run with two different noninductive graupel-ice charge separation schemes, for a total of 22 simulations. Results show that the relationships between total flash rate and rain mass, ice crystal mass flux, and graupel volume are significant, while the relationships are weak for electric field and maximum updraft. In cases where convection remained isolated (i.e., one cell in the model domain for most of the 120 minutes), the correlations between detrended total flash rate and graupel volume were also found to be significant. Additionally, by translating flash rate time series backwards in time, the correlation coefficients between flash rates and some of the microphysical variables were found to increase. Understanding these relationships can provide the foundation for future work in predicting flash rates across a wide range of storms based on observational information, including radar data.

Available online at ://http://ams.confex.com/ams/88Annual/techprogram/paper_133415.htm.

Cohn, S. J., J. Hallett, J. M. Lewis, 2006: Teaching graduate atmospheric measurement. Bulletin of the American Meteorological Society, 87, 1673-1678.

Coniglio, M. C., H. E. Brooks, S. J. Weiss, 2005: Use of proximity sounding parameters to improve the prediction of MCS speed and demise. 21st Conference on Weather Analysis and Forecasting, Washington, DC, USA, American Meteorological Society, 3.3.

Coniglio, M. C., D. J. Stensrud, L. J. Wicker, 2006: Effects of upper-level shear on the structure and maintenance of strong quasi-linear mesoscale convective systems. Journal of the Atmospheric Sciences, 63, 1231-1252.

Recent observational studies have shown that strong midlatitude mesoscale convective systems (MCSs) tend to decay as they move into environments with less instability and smaller deep-layer vertical wind shear. These observed shear profiles that contain significant upper-level shear are often different from the shear profiles considered to be the most favorable for the maintenance of strong, long-lived convective systems in some past idealized simulations. Thus, to explore the role of upper-level shear in strong MCS environments, a set of two-dimensional (2D) simulations of density currents within a dry, statically neutral environment is used to quantify the dependence of lifting along an idealized cold pool on the upper-level shear. A set of three-dimensional (3D) simulations of MCSs is produced to gauge the effects of the upper-level shear in a more realistic framework.

Results from the 2D experiments show that the addition of upper-level shear to a wind profile with weak to moderate low-level shear increases the vertical displacement of parcels despite a decrease in the vertical velocity along the cold pool interface. Parcels that are elevated above the surface (1–2 km) overturn and are responsible for the deep lifting in the deep-shear environments, while the surface-based parcels typically are lifted through the cold pool region in a rearward-sloping path. This deep overturning helps to maintain the leading convection and greatly increases the size and total precipitation output of the convective systems in more complex 3D simulations, even in the presence of 3D structures. These results show that the shear profile throughout the entire troposphere must be considered to gain a more complete understanding of the structure and maintenance of strong midlatitude MCSs.

Coniglio, M. C., S. F. Corfidi, 2006: Forecasting the speed and maintenance of severe mesoscale convective systems. Extended Abstracts, Severe Local Storms Symposium at the 86th AMS annual meeting, Atlanta, GA, USA, American Meteorological Society, CD-ROM, P1.30. [Available from National Weather Center, 120 David L. Boren Blvd, Norman, OK, USA, 73071.]

Available online at ://http://ams.confex.com/ams/pdfpapers/104815.pdf.

Coniglio, M. C., H. E. Brooks, S. F. Corfidi, S. J. Weiss, 2007: Forecasting the Maintenance of Quasi-Linear Mesoscale Convective Systems. Weather and Forecasting, 22, 556-570.

The problem of forecasting the maintenance of mesoscale convective systems (MCSs) is investigated through an examination of observed proximity soundings. Furthermore, environmental variables that are statistically different between mature and weakening MCSs are input into a logistic regression procedure to develop probabilistic guidance on MCS maintenance, focusing on warm-season quasi-linear systems that persist for several hours.
Between the mature and weakening MCSs, shear vector magnitudes over very deep layers are the best discriminators among hundreds of kinematic and thermodynamic variables. An analysis of the shear profiles reveals that the shear component perpendicular to MCS motion (usually parallel to the leading line) accounts for much of this difference in low levels and the shear component parallel to MCS motion accounts for much of this difference in mid-to-upper levels. The lapse rates over a significant portion of the convective cloud layer, the convective available potential energy, and the deep-layer mean wind speed are also very good discriminators and collectively provide a high level of discrimination between the mature and dissipation soundings as revealed by linear discriminant analysis. Probabilistic equations developed from these variables used with short-term numerical model output show utility in forecasting the transition of an MCS with a solid line of 50+ dbZ echoes to a more disorganized system with unsteady changes in structure and propagation. This study shows that empirical forecast tools based on environmental relationships still have the potential to provide forecasters with improved information on the qualitative characteristics of MCS structure and longevity. This is especially important since the current and near-term value added by explicit numerical forecasts of convection is still uncertain.

Coniglio, M. C., D. C. Dowell, L. J. Wicker, 2007: Ensemble Kalman filter assimilation of Doppler radar data: Analyses of a developing MCS. Extended Abstracts, 22nd Conference on Weather Analysis and Forecasting/18th Conference on Numerical Weather Prediction, Park City, UT, USA, American Meteorlogical Society, 3B.3. [Available from Michael Coniglio, NSSL/FRDD, 120 David L. Boren Blvd, Norman, OK, USA, 73072.]

Recent efforts at the National Severe Storms Laboratory and the University of Oklahoma/Center for Analysis and Prediction of Storms have shown the positive impact of assimilating real Doppler velocity and reflectivity observations using an Ensemble Kalman Filter (EnKF) technique for the storm-scale analysis of supercell thunderstorms. Recently, the utility of this technique to other convective modes with multiple updrafts and more complex evolutions has been shown with analyses of the 16-17 June 2005 severe bow echo MCS across Oklahoma. It is well known that an accurate depiction of convective system cold pools is a prerequisite for the accurate short-term (1-12 h) prediction of MCSs by high-resolution numerical models. One of the most promising aspects of the analysis is the detailed and accurate depiction of the cold convective outflow and the robustness of the analyses to changes in the experimental design (although the well-known sensitivity to microphysics is still apparent). This talk will highlight the successful analysis of this event and discuss the mechanics of the EnKF procedure applied to a real and complex convective situation. In addition, the relative merits of 1-h forecasts produced from the EnKF analyses and the many outstanding issues that need to be addressed before these techniques can be applied in real time will be discussed.

Available online at ://http://ams.confex.com/ams/pdfpapers/124285.pdf.

Coniglio, M. C., J. S. Kain, S. J. Weiss, M. Xue, M. L. Weisman, Z. I. Janjic, 2007: Evaluating storm-scale model output for severe-weather forecasting: The 2007 NOAA HWT Spring Experiment.. Preprints, 4th European Conference on Severe Storms, Trieste, Italy, International Centre for Theoretical Physics, CD-ROM, 03.11.

Coniglio, M. C., A. E. Cohen, S. F. Corfidi, S. J. Corfidi, 2007: Discrimination of MCS environments using sounding observations. Weather and Forecasting, 22, 1045-1062.

The prediction of the strength of mesoscale convective systems (MCSs) is a major concern to operational meteorologists and the public. To address this forecast problem, this study examines meteorological variables derived from sounding observations taken in the environment of quasi-linear MCSs. A set of 186 soundings that sampled the beginning and mature stages of the MCSs are categorized by their production of severe surface winds into weak, severe, and derecho-producing MCSs. Differences in the variables among these three MCS categories are identified and discussed. Mean low- to upper-level wind speeds and deep-layer vertical wind shear, especially the component perpendicular to the convective line, are excellent discriminators among all three categories. Low-level inflow relative to the system is found to be an excellent discriminator, largely because of the strong relationship of system severity to system speed. Examination of the mean wind and shear vectors relative to MCS motion suggests that cell propagation along the direction of cell advection is a trait that separates severe, long-lived MCSs from the slower-moving, nonsevere variety and that this is favored when both the deep-layer shear vector and the mean deep-layer wind are large and nearly parallel. Midlevel environmental lapse rates are found to be very good discriminators among all three MCS categories, while vertical differences in equivalent potential temperature and CAPE only discriminate well between weak and severe/derecho MCS environments. Knowledge of these variables and their distribution among the different categories of MCS intensity can be used to improve forecasts and convective watches for organized convective wind events.

Coniglio, M. C., J. S. Kain, S. J. Weiss, D. R. Bright, J. J. Levit, M. Xue, M. L. Weisman, Z. I. Janjic, M. Pyle, J. Du, D. J. Stensrud, 2007: Evaluating WRF model output for severe-weather forecasting: The 2007 NOAA HWT Spring Experiment.. Extended Abstracts, 22th Conference on Weather Analysis and Forecasting/18th Conference on Numerical Weather Prediction, Park City, UT, USA, American Meteorological Society, CD-ROM, 11A.2.

Coniglio, M. C., M. Bardon, K. Virts, S. J. Weiss, 2006: Forecasting the maintenance of mesoscale convective systems.. Extended Abstracts, 23rd Conf. on Severe Local Storms, St. Louis, MO, USA, American Meteorological Society, CD-ROM, 2.3.

Dabberdt, W. F., T. W. Schlatter, F. H. Carr, E. W. Friday, D. P. Jorgensen, S. Koch, M. Pirone, F. M. Ralph, J. Sun, P. Welsh, X. Zou, 2005: Multi-Functional Mesoscale Observing Networks. Bulletin of the American Meteorological Society, 86, 961-982.

The U.S. Weather Research Program (USWRP) sponsored a community workshop on the design and development of multifunctional mesoscale observing networks in support of integrated forecasting systems, on 8–10 December 2003 at the National Center for Atmospheric Research in Boulder, Colorado. The workshop goals were to identify challenges, needs, and opportunities involved in developing improved, economically viable, integrated atmospheric mesoscale observing, modeling, and information-delivery systems. Recommendations were sought for improved mesoscale observing networks that recognize the needs of users, modelers, and forecasters.

Dodson, A., S. Van Cooten, K. Howard, J. Zhang, X. Xu, 2008: Assessing Vertical Profiles of Reflectivity (VPR's) To Detect Extreme Rainfall: Implications for Flash Flood Monitoring and Prediction. Preprints, 22nd Conference on Hydrology- Session 1, Weather To Climate Scale Hydrological Forecasting, New Orleans, LA, USA, AMS, CD-ROM, 1.5.

Tropical Storm Barry moved across the state of Florida from Tampa to Jacksonville on June 2 and then became extratropical as it moved northeast along the coastlines of Georgia, South Carolina and North Carolina from June 3 to June 4, 2007. Rainfall reports from gauges located within the surveillance areas of the Wakefield, Virginia (AKQ), Raleigh-Durham, North Carolina (RDU), and Morehead City, North Carolina (MHX), NEXRAD sites were collected and processed to document hourly rainfall rates associated with the system. In addition to the gauge data, atmospheric soundings from six area upper air observing sites were archived and analyzed to determine the response of atmospheric conditions, specifically freezing level, precipitable water, and atmospheric instability, as the system affected the region.

NOAA's National Severe Storms Laboratory (NSSL) Q2 System (www. nmq.nssl.noaa.gov) produces Vertical Profiles of Reflectivity (VPR) every five minutes for each continental United States (CONUS) NEXRAD site. These VPRs are used in the production of five-minute multi-sensor Quantitative Precipitation Estimates (QPE) to provide constantly updated relationships between radar reflectivity factor, Z, and rain rate, R (Z-R). VPRs were archived for June 3 and 4 for AKQ, RDU, and MHX. The VPRs were analyzed to quantify radar reflectivity trends over the course of the storm event. These trends were then correlated with rainfall rates, atmospheric sounding data, and surface observations, to investigate the characteristics of the VPRs associated with the highest rainfall rates. Results of this analysis indicate VPRs associated with the highest hourly rainfall rates observed with the storm system occurred as VPRs lost a concentrated area of high reflectivities around the atmospheric freezing level. Additionally, the gradient of radar reflectivities above and below this dissipating high reflectivity area diminished. Atmospheric soundings and surface map analysis indicated the air mass characteristics were acquiring tropical characteristics as surface dew points and atmospheric water content were increasing, wind directions transitioned from westerly to an easterly fetch off the Atlantic Ocean, and the atmospheric freezing level was rising. As the storm system moved away from the Carolinas, VPRs began to regain a concentrated area of high reflectivities around the atmospheric freezing level and the gradient of radar reflectivities began to increase once again above and below the area of higher reflectivities.

To quantify the implications of these VPR characteristics on the accuracy of the Q2 system's five-minute multi-sensor Quantitative Precipitation Estimates (QPE), the Q2 statistical verification tools were used to evaluate the performance of the system during the periods of the most intense rainfall. The Q2 system has recently implemented a tropical rain Z-R when VPRs and atmospheric sounding data meet criteria which have been identified by NSSL scientists as common factors in intense rainfall events. The VPRs observed through this June, 2007 storm event, were consistent with their findings. Results of this assessment show the Q2 tropical Z-R relationship produced highly accurate precipitation estimates which are available at a 1 km grid mesh resolution every five minutes. Additionally, the dynamic VPR system captured the air mass changes which occurred during the event. This feature provides improved information on a storm's environment to determine appropriate radar Z-R adjustments. This case demonstrates the ability to increase the accuracy of precipitation estimates especially in ungauged locations which can improve NOAA and our nation's flash flood monitoring and prediction programs.

Available online at ://http://ams.confex.com/ams/88Annual/techprogram/paper_135143.htm.

Engerer, N. A., D. J. Stensrud, M. C. Coniglio, 2008: Surface Characteristics of Observed Cold Pools. Monthly Weather Review, 136, 4839-4849.

Cold pools are a key element in the organization of precipitating convective systems, yet knowledge of their typical surface characteristics is largely anecdotal. To help alleviate this situation, cold pools from 39 mesoscale convective system (MCS) events are sampled using Oklahoma Mesonet surface observations. One thousand three hundred and eighty-nine time series of surface observations are used to determine typical rises in surface pressure and decreases in temperature, potential temperature, and equivalent potential temperature associated with the cold pool, and the maximum wind speeds in the cold pool. The data are separated into one of four convective system lifecycle stages: first storms, MCS initiation, mature MCS, and MCS dissipation. Results indicate that the mean surface pressure rises associated with cold pools increase from 3.2 hPa for the first storms lifecycle stage to 4.5 hPa for the mature MCS stage before dropping to 3.3 hPa for the dissipation stage. In contrast, the mean temperature (potential temperature) deficits associated with cold pools decrease from 9.5 K (9.8 K) to 5.4 K (5.6 K) from the first storms to dissipation stage, with a decrease of approximately 1 K associated with each advance in lifecycle stage. However, the daytime and early evening observations show mean temperature deficits over 11 K. A comparison of these observed cold pool characteristics with results from idealized numerical simulations of MCSs suggests that observed cold pools likely are stronger than those found in model simulations, particularly when ice processes are neglected in the microphysics parameterization. The mean deficits in equivalent potential temperature also decrease with MCS lifecycle stage, starting at 21.6 K for first storms and dropping to 13.9 K for dissipation. Mean wind gusts are above 15 m s-1 for all lifecycle stages. These results should help numerical modelers determine if the cold pools in high-resolution models are in reasonable agreement with the observed characteristics found herein. Thunderstorm simulations and forecasts with thin model layers near the surface also are needed to obtain better representations of cold pool surface characteristics that can be compared with observations.

Fast, J. D., R. K. Newsom, K. J. Allwine, Q. Xu, P. Zhang, J. H. Copeland, J. Sun, 2007: Using NEXRAD wind retrievals as input to atmospheric dispersion models. Extended Abstracts, Seventh Symposium on the Urban Environment, San Diego, CA, USA, Amer. Meteor. Soc., 8.2.

Available online at ://http://ams.confex.com/ams/7Coastal7Urban/techprogram/paper_127244.htm.

Fast, J. D., R. K. Newsom, K. J. Allwine, Q. Xu, P. Zhang, J. Copeland, J. Sun, 2008: An evaluation of two NEXRAD wind retrieval methedologies and their use in atmospheric dispersion models. Journal of Applied Meteorology and Climatology, 47, 2351-2371.

Fierro, A. O., L. Leslie, E. R. Mansell, G. J. Holland, J. M. Straka, 2006: Numerical simulations of the evolution of tropical cyclone electrification, lightning, microphysics, and dynamics at landfall: preliminary results. Preprints, Second Conference on Meteorological Applications of Lightning Data, Atlanta, GA, USA, American Meteorological Society, CD-ROM, P1.12.

Providing accurate and timely forecasts of the intensity and location of landfalling tropical cyclones (TCs) is a major meteorological challenge, and is increasingly important as coastal regions affected become more populated. A major unsolved problem is why TCs vary so much in their electrical activity. Some storms have little lightning activity, while others are extremely active, especially in their spiral cloud bands or within their eyewall as they intensify or weaken. At present, little is known about the evolution of charge and subsequent electrification in hurricanes, so our early results are a guideline for future studies. The findings are expected to have major implications for TC predictions and lightning observation strategies at landfall. We suggest that they may also lead to improved understanding of TC structure in general.

Toward this goal, a sophisticated cloud model featuring a 10-ICE microphysics scheme and a 3D branched lightning module explores the utility of a systematic monitoring of lightning activity such as flash rate, cloud to ground polarity and stroke multiplicity within TCs, as they strengthen or weaken over the ocean, especially when they make landfall. Of interest is how the microphysical and subsequent charge structure differs from, or resembles, that of electrically active continental convective systems such as supercells or mesoscale convective systems. A preliminary set of high-resolution numerical simulations were performed on a fine grid having a horizontal grid spacing of 3km and a vertical mean spacing of 600 m (45 height levels). The environmental initial conditions were from a composite sounding from TC Charley (2004), which showed a clear increase in lightning activity before intensifying from a borderline Category 3 to a high-end Category 4 storm on the Saffir-Simpson scale 8 hours before landfall on the west Florida coast. A meridionally orientated horizontal slab moving towards the TC at a fixed constant speed (of 8 m/s) was used as an initial simulation of landfall. More sophisticated landfall representations are being developed.

Preliminary results show that the highest total lightning flash rate are found within the stronger cells forming the outer rainbands and within the eyewall, where updraft speeds seldom exceed 15 m/s, consistent with observations. Significant charging capable to produce lightning flashes are collocated with regions having moderate graupel mixing ratio (> 0.5 g/kg) and moderate LWC (> 1 g/kg), namely within the eyewall and the strongest outer band cells. Using the Gardiner non-inductive scheme and weak inductive charging settings, the eyewall exhibits a normal tripole charge structure while a normal dipole is observed in the outer eyewall startiform region as induction responsible for the formation/enhancement of the lowest charge region becomes negligible there. The charges forming the dipole in the outer eyewall are generated within the eyewall via non-inductive collisional charging between graupel pellets and lighter ice crystals in the mixed-phase region at midlevels (~-15C isotherm level at 7km AGL) and are ejected radially outward by the centripetal force induced by the storm intense circulation at and near its center.

Available online at ://http://ams.confex.com/ams/Annual2006/techprogram/paper_103235.htm.

Fierro, A. O., M. S. Gilmore, L. J. Wicker, E. R. Mansell, J. M. Straka, 2006: Electrification and lightning in an idealized boundary-crossing supercell simulation of 2 June 1995. Monthly Weather Review, 134, 3171.

A nonhydrostatic cloud model with electrification and lightning processes was utilized to investigate how simulated supercell thunderstorms respond when they move into environments favorable for storm intensification. One model simulation was initialized with an idealized horizontally varying environment, characteristic of that observed across an outflow boundary in the west Texas Panhandle on 2 June 1995 with larger convective available potential energy (CAPE) and wind shear on the boundary’s cool side. That simulation was compared with a control simulation initialized without the boundary. The simulated right-moving supercell rapidly increased in updraft strength and volume, low-level rotation, radar reflectivity, and 40-dBZ echo-top height as it crossed the boundary, whereas the supercell that did not cross the boundary failed to intensify. For the same kinematic and microphysical evolution and the same inductive charging parameterization, four noninductive (NI) charging parameterizations were tested. In all four cases, there was a general tendency for the charge regions to be lofted higher within the updraft after crossing the boundary. Once the precipitation regions between the main storm and a secondary storm started merging farther on the cool side of the boundary, a gradual deepening and strengthening of the lowest charge regions occurred with relatively large increases in hail and graupel volume, charging rates, charge volume, charge density, and intracloud and cloud-to-ground (CG) flash rates. The negative charge present on graupel within the downdraft appeared to have a common origin via strong NI charging within the midlevel updraft in all four NI cases. Positive channels were more consistent in coming closer to the ground with time compared to negative channels within this graupel and hail-filled downdraft (four of four cases). Those NI schemes that also set up a positive dipole (three of four cases) or inverted tripole (two of four cases) above the downdraft had downward-propagating positive channels that reached ground as positive CG (+CG) flashes. The best overall performance relative to the 2 June 1995 CG lightning observations occurred within one of the rime-accretion-rate-based schemes and the Gardiner scheme as parameterized by Ziegler.

Fierro, A. O., L. Leslie, E. Mansell, J. Straka, D. MacGorman, C. Ziegler, 2007: A High-resolution Simulation of Microphysics and Electrification in an Idealized Hurricane-like Vortex. Meteorology and Atmospheric Physics, 98, 13-33.

Cloud-to-ground (CG) lightning bursts in the eyewall of mature tropical cyclones (TCs) are believed to be good indicators of imminent intensification of these systems. While numerous well-documented observational cases exist in the literature, no modeling studies of the electrification processes within TCs have previously been conducted. At present, little is known about the evolution of charge regions and lightning activity in mature TCs. Towards this goal, a numerical cloud model featuring a 12-class bulk microphysics scheme with electrification and lightning processes is utilized to investigate the evolution of the microphysics fields and subsequent electrical activity in an idealized hurricane-like vortex.

Preliminary results show that the highest total lightning flash rates (CG plus intracloud) are primarily found within the eyewall where updraft speeds tend to be larger than elsewhere in the TC, though rarely exceeding 10 m s^-1. Smaller total flash rates are also found within the strongest cells forming the outer bands, where updraft speeds sometimes reach 15 m s^-1. As expected, these two regions of the storm are generally characterized by moderate total graupel mixing ratio (> 0.5 g kg^-1) and moderate cloud water content (> 0.2 g m^-3). When the model uses the Saunders and Peck non-inductive (NI) charging scheme and moderate inductive charging settings, the inner eyewall region exhibits a complex charge structure. However, the charge regions involved in lightning can be described as a normal tripole charge structure in the eyewall, while a normal dipole is observed in the outer eyewall stratiform region and in the strongest cells forming the outer rainbands. The charges forming the normal dipole in the outer eyewall are generated within the eyewall via NI charging in the mixed-phase region at mid-levels (near the -10 deg C isotherm) and later, are ejected radially outward by the storm’s intense circulation.

Fujita, T., D. J. Stensrud, D. C. Dowell, 2005: Surface data assimilation using an ensemble Kalman filter approach with initial condition and model physics uncertainties. Preprints, 11th Conf. on Mesoscale Processes, Albuquerque, NM, USA, American Meteorological Society, CD-ROM, 1M.3.

Fujita, T., D. J. Stensrud, D. C. Dowell, 2007: Surface data assimilation using an ensemble Kalman filter approach with initial condition and model physics uncertainty. Monthly Weather Review, 135, 1846-1868.

The assimilation of surface observations using an ensemble Kalman filter (EnKF) approach is evaluated for the potential to improve short-range forecasting. Two severe weather cases are examined, in which the assimilation is performed over a 6-h period using hourly surface observations followed by an 18-h simulation period. Ensembles are created in three different ways, by using different initial and boundary conditions, by using different model physical process schemes, and by using both different initial and boundary conditions and different model physical process schemes. The ensembles are compared in order to investigate the role of uncertainties in the initial and boundary conditions and physical process schemes in EnKF data assimilation. In the initial condition ensemble, spread is associated largely with the displacement of atmospheric baroclinic systems. In the physics ensemble, spread comes from the differences in model physics, which results in larger spread in temperature and dewpoint temperature than the initial condition ensemble, and smaller spread in the wind fields. The combined initial condition and physics ensemble has properties from both of the previous two ensembles. It provides the largest spread and produces the best simulation for most of the variables, in terms of the rms difference between the ensemble mean and observations. Perhaps most importantly, this combined ensemble provides very good guidance on the mesoscale features important to the severe weather events of the day.

Fujita, T., D. J. Stensrud, D. C. Dowell, 2008: Using Precipitation Observations in a Mesoscale Short-Range Ensemble Analysis and Forecasting System. Weather and Forecasting, 23, 357-372.

A simple method to assimilate precipitation data from a synthesis of radar and gauge data is developed to operate alongside an ensemble Kalman filter that assimilates hourly surface observations. The mesoscale ensemble forecast system consists of 25 members with 30-km grid spacing and incorporates variability in both initial and boundary conditions and model physical process schemes. The precipitation assimilation method only incorporates information on when and where rainfall is observed. Model temperature and water vapor mixing ratio profiles at each grid point are modified if rainfall is observed but not predicted, or if rainfall is predicted but not observed. These modifications act to either increase or decrease, respectively, the likelihood that precipitation develops at that grid point.

Two cases are examined in which this technique is applied to assimilate precipitation data every 15 min from 1200 to 1800 UTC, while hourly surface observations are also assimilated at the same time using the more sophisticated ensemble Kalman filter approach. Results show that the simple method for assimilating precipitation data helps the model develop precipitation where it is observed, resulting in the precipitation area being reproduced more accurately than in the run without precipitation-data assimilation, while not negatively influencing the positive results from the surface data assimilation. Improvement is also seen in the reliability of precipitation probabilities for a 1 mm h−1 threshold after the assimilation period, indicating that assimilating precipitation data may provide improved forecasts of the mesoscale environment for a few hours.

Gao, J., M. Xue, S. Lee, A. Shapiro, Q. Xu, K. K. Droegemeier, 2006: A three-dimensional variational single-doppler velocity retrieval method with simple conservation equation constraint. Meteorol. Atmos. Phys., 94, 11-26.

Godfrey, C. M., D. J. Stensrud, L. M. Leslie, 2005: The influence of improved land surface and soil data on mesoscale model predictions. Proc. 19th Conference on Hydrology, San Diego, CA, USA, American Meteorological Society, CD-ROM, 4.7.

One of the most difficult aspects in the evaluation of land surface models is the lack of observational data for accurate specification of the model initial conditions. Routine observations of fractional vegetation coverage and leaf area index (LAI) are not available at high resolution (~1 km), nor are observations of soil moisture and soil temperature. This gap in our observational capabilities seriously hampers the evaluation and improvement of land surface model parameterizations, since model errors may be related to improper initial conditions as much as to inaccuracies in the model formulations. To overcome these difficulties, two unique data sets are used. First, fractional vegetation coverage and LAI are derived from biweekly maximum normalized difference vegetation index (NDVI) composites at 1 km resolution obtained from daily observations by the Advanced Very High Resolution Radiometer (AVHRR) onboard National Oceanic and Atmospheric Administration satellites. Second, the Oklahoma Mesonet measures soil moisture and soil temperature at 15-minute intervals. Combined, these two data sets provide significantly improved initial conditions for land surface models and allow us to evaluate the utility of the land surface models with much greater confidence and detail than previously.

The value of these two data sources to land surface model initializations is evaluated using the Penn State-NCAR fifth-generation Mesoscale Model (MM5). Forecasts that both include and neglect these unique land surface observations are compared. Results are verified against the dense network of surface observations afforded by the Oklahoma Mesonet, including surface flux data derived from special sensors available at some of the Mesonet sites. Implications for further data requirements are discussed.

Godfrey, C. M., D. J. Stensrud, L. M. Leslie, 2006: Soil temperature and moisture errors in Eta model analyses. Proc. 20th Conf. on Hydrology, Atlanta, GA, USA, Amer. Meteor. Soc., CD-ROM, JP1.2.

Forecast models require accurate soil temperature and soil moisture conditions to be able to properly partition the surface heat fluxes that drive the evolution of the planetary boundary layer. The National Centers for Environmental Prediction (NCEP) operational Eta model produces land surface analyses by continuously cycling soil temperature and moisture fields. In the past, these fields evolved only in response to radiation budget constraints and modeled precipitation, but NCEP recently upgraded the self-cycling process to assimilate observed precipitation. This study highlights potential problems with the land surface analysis from the Eta model by comparing 00 UTC and 12 UTC Eta model analyses of soil temperature and moisture at several depths with observations from the Oklahoma Mesonet. There are strong biases in soil temperature and there is a severe underestimation of soil moisture at all depths. There is notable improvement in the analyzed soil moisture fields after the change to a new assimilation scheme. While this change reduced the magnitude of the errors, a strong dry bias persists in the soil moisture field. A simple one-layer slab soil model reveals that these soil moisture errors alone may account for 1.0-1.5 degrees Celsius increases in maximum soil temperatures during the day and reductions in soil temperatures at night of 0.3-0.8 degrees Celsius. The remaining soil temperature errors likely stem from documented problems with the solar radiation and longwave parameterizations within the Eta model.

Available online at ://http://www.cimms.ou.edu/~cgodfrey/landsfc/.

Godfrey, C. M., D. J. Stensrud, 2008: Soil Temperature and Moisture Errors in Operational Eta Model Analyses. Journal of Hydrometeorology, 9, 367-387.

Proper partitioning of the surface heat fluxes that drive the evolution of the planetary boundary layer in numerical weather prediction models requires an accurate specification of the initial state of the land surface. The National Centers for Environmental Prediction (NCEP) operational Eta Model is used to produce land surface analyses by continuously cycling soil temperature and moisture fields. These fields previously evolved only in response to radiation budget constraints and modeled precipitation, but NCEP recently upgraded the self-cycling process so that soil fields respond instead to the radiation budget and observed precipitation. A comparison of 0000 and 1200 UTC Eta Model analyses of soil temperature and moisture at several soil depths with observations from the Oklahoma Mesonet during 2004 and 2005 shows that there are strong biases in soil temperature and a severe underestimation of soil moisture at all depths. After the change to a new assimilation scheme, there is notable improvement in the magnitude of the analyzed soil moisture fields, although a strong dry bias persists in the soil moisture field. A simple one-layer slab soil model quantifies the effect of such soil moisture errors on the diurnal cycle of soil temperature and reveals that these soil moisture errors alone may account for only 1.6°C increases in predicted maximum soil temperatures during the day and temperature reductions of the same magnitude at night. The much larger remaining soil temperature errors possibly stem from documented problems with the solar radiation and longwave parameterizations within the Eta Model.

Hane, C. E., D. L. Andra Jr., K. Trammell, F. H. Carr, 2005: Development of a tool to aid in forecasting the evolution of Great Plains MCSs during late morning hours. AIRMASS 2005 Conference, Wichita, KS, USA, American Meteorological Society, CD-ROM, XXXX.

Hane, C. E., D. L. Andra, Jr., J. A. Haynes, T. E. Thompson, F. H. Carr, 2005: On the Importance of Environmental Factors in Influencing the Evolution of Morning Great Plains MCS Activity during the Warm Season. Extended Abstracts, Eleventh Conference on Mesoscale Processes, Albuquerque, NM, USA, American Meteorological Society, CD-ROM, P3M.6.

Hane, C. E., J. A. Haynes, D. L. Andra, F. H. Carr, 2008: The evolution of morning convective systems over the U.S. Great Plains during the warm season. Part II: A climatology and the influence of environmental factors. Monthly Weather Review, 136, 929-944.

Mesoscale convective systems that affect a limited area within the southern plains of the United States during late morning hours during the warm season are investigated. A climatological study over a 5-yr period documents the initiation locations and times, tracks, associated severe weather, and relation to synoptic features over the lifetimes of 145 systems. An assessment is also made of system evolution in each case during the late morning. For a subset of 48 systems, vertical profiles of basic variables from Rapid Update Cycle (RUC) model analyses are used to characterize the environment of each system. Scatter diagrams and discriminant analyses are used to assess which environmental variables are most promising in helping to determine which of two classes of evolutionary character each system will follow

Harasti, P. R., D. Smalley, M. Weber, C. Kessinger, Q. Xu, P. Zhang, S. Liu, T. Tsui, J. Cook, Q. Zhao, 2005: On the development of a multi-algorithm radar data quality control system at the naval research laboratory. 32nd Conference on Radar Meteorology, Albuquerque, NM, USA, American Meteorological Society, CD-ROM, XXXX.

Heinselman, P., S. Weiss, M. Coniglio, D. Andra, G. Stumpf, B. Phillips, J. Brotzge, cited 2008: 2008 Spring HWT Experiments at the NWC. [Available online at ://http://www.nwas.org/newsletters/pdf/news_october2008.pdf.]

Heinselman, P. L., D. J. Stensrud, R. M. Hluchan, P. L. Spencer, P. C. Burke, K. L. Elmore, 2008: Radar reflectivity-based estimates of mixed-layer depth. Journal of Atmospheric and Oceanic Technology, Web, .

This study investigates the potential for estimating mixed-layer depth by taking advantage of the radial gradients in the radar reflectivity field produced by the large vertical gradients in water vapor mixing ratio that are characteristic of the mixing height. During the day, this relationship often results in a ring of maximum reflectivity observed to progress radially outward from the radar as mixed-layer depth increases. A comparison of mixed-layer depths estimated from the Oklahoma City WSR-88D (KTLX) with those estimated from a nearby 915 MHz profiler reveals that mixed-layer depths from the WSR-88D are slightly too high (up to 0.3 km) during the first three hours of the diurnal cycle, nearly unbiased midday, and slightly too low (0.2 km or less) thereafter. The procedure estimates mixed-layer depths only during the daytime hours from 1300–2300 UTC. The weather conditions for the 17 days studied were fairly quiescent, with sunny skies and light winds.

Early Release

Homar, V., D. J. Stensrud, J. J. Levit, D. R. Bright, 2006: Value of Human-Generated Perturbations in Short-Range Ensemble Forecasts of Severe Weather. Weather and Forecasting, 21, 347-363.

During the spring of 2003, the Storm Prediction Center, in partnership with the National Severe Storms Laboratory, conducted an experiment to explore the value of having operational severe weather forecasters involved in the generation of a short-range ensemble forecasting system. The idea was to create a customized ensemble to provide guidance on the severe weather threat over the following 48 h. The forecaster was asked to highlight structures of interest in the control run and, using an adjoint model, a set of perturbations was obtained and used to generate a 32-member fifth-generation Pennsylvania State University–National Center for Atmospheric Research Mesoscale Model (MM5) ensemble. The performance of this experimental ensemble is objectively evaluated and compared with other available forecasts (both deterministic and ensemble) using real-time severe weather reports and precipitation in the central and eastern parts of the continental United States. The experimental ensemble outperforms the operational forecasts considered in the study for episodes with moderate-to-high probability of severe weather occurrence and those with moderate probability of heavy precipitation. On the other hand, the experimental ensemble forecasts of low-probability severe weather and low precipitation amounts have less skill than the operational models, arguably due to the lack of global dispersion in a system designed to target the spread over specific areas of concern for severe weather. Results from an additional test ensemble constructed by combining automatic and manually perturbed members show the best results for numerical forecasts of severe weather for all probability values. While the value of human contribution in the numerical forecast is demonstrated, further research is needed to determine how to better use the skill and experience of the forecaster in the construction of short-range ensembles.

Homar, V., D. J. Stensrud, 2008: Subjective versus objective sensitivity estimates: application to a North African cyclogenesis. Tellus, 60A, 1064-1078.

An observing system simulation experiment is used to test and compare objective and subjective estimates of sensitivity of a forecast aspect to the initial condition (IC) fields for a case of rapidly developing cyclogenesis over the Western Mediterranean during 19–22 December 1979. The ability of sensitivity estimation methods to provide helpful guidance about where an improvement in the IC can lead to the largest forecast error reduction is particularly important to ascertain in order to guide adaptive observation campaigns.

Synthetic soundings from a 15-km reference simulation are added to an initially poor 60-km control simulation over the sensitive areas as determined by the combination of the given sensitivity estimate and a simple analysis error estimate. The ability of each sensitivity estimation method to produce an improved simulation of the cyclone is assessed.

Results show that while the sensitivity estimates perform similarly, with no significant differences among them, the subjective method yields the best overall targeting guidance. In contrast, the adjoint estimate provides the least accurate targeting guidance for this particular case and analysis error estimate. This suggests that subjective sensitivity estimation methods are able to compete with or even improve upon the objective estimation method for this case of cyclogenesis over the Western Mediterranean.

James, M. R., R. D. Palmer, T.-Y. Yu, S. M. Torres, R. J. Doviak, D. S. Zrnic, 2005: Implementation of refractivity retrieval from ground clutter using the S-band KOUN radar. Preprints, 32nd International Conference on Radar Meteorology, Albuquerque, NM, USA, American Meteorological Society, 4R.7.

Johnson, E. V., E. R. Mansell, 2006: Three dimensional lightning mapping of the central Oklahoma supercell on 26 May 2004. Extended Abstracts, Second Conference on Meteorological Applications of Lightning Data, Atlanta, GA, USA, American Meteorological Society, CD-ROM, 6.5.

Three-dimensional lightning mapping observations from the Oklahoma Lightning Mapping Array (OK-LMA) were used to analyze charge structure of a splitting supercell on 26 May 2004 during the Thunderstorm Electrification and Lightning Experiment (TELEX). The OK-LMA was used to evaluate cloud-to-ground (CG) flashes reported by the National Lightning Detection Network's (NLDN). Each NLDN flash between 2300 UTC and 2310 UTC was classified as either a CG or an intra-cloud (IC) flash using LMA-inferred charge structure. The LMA analysis of the charge structure supports charge structure for 23% of the positive CGs. Most of the negative NLDN flashes that were analyzed were not confirmed by the LMA.

Available online at ://http://ams.confex.com/ams/Annual2006/techprogram/paper_104352.htm.

Kain, J. S., S. J. Weiss, S. R. Dembek, J. J. Levit, D. R. Bright, J. L. Case, M. C. Coniglio, A. R. Dean, R. Sobash, 2008: Severe-weather forecast guidance from the first generation of large domain convection-allowing models: Challenges and opportunities. Preprints, 24th Conference on Severe Local Storms, Savannah, GA, USA, Amer. Meteor Soc., CD-ROM, 12.1. [Available from John Kain, NSSL, 120 David L. Boren Blvd., Norman, OK, USA, 73072.]

Kong, F., M. XUE, D. R. Bright, M. C. Coniglio, K. W. Thomas, Y. Wang, D. Weber, J. S. Kain, S. J. Weiss, J. Du, 2007: Preliminary analysis on the real-time storm-scale ensemble forecasts produced as a part of the NOAA Hazardous Weather Testbed 2007 Spring Experiment.. Preprints, Preprints, 22th Conference on Weather Analysis and Forecasting/18th Conference on Numerical Weather Prediction, Park City, UT, USA, Amer. Meteor. Soc, CD-ROM, 3B.2.

Kong, F., M. Xue, D. R. Bright, M. C. Coniglio, K. W. Thomas, Y. Wang, D. B. Weber, J. S. Kain, S. J. Weiss, J. Du, 2007: Preliminary analysis on the real-time storm-scale ensemble forecasts produced as a part of the NOAA Hazardous Weather Testbed 2007 Spring Experiment. Preprints, 22th Conference on Weather Analysis and Forecasting/18th Conference on Numerical Weather Prediction, Park City, UT, USA, Amer. Meteor. Soc., CD-ROM, 3B.2. [Available from Fanyou Kong, CAPS, 120 David L. Boren Blvd., Norman, OK, USA, 73072.]

A real-time storm-scale WRF-ARW-based ensemble forecast system at 4-km resolution is being developed at CAPS and will be run daily for 33 hours as part of the NOAA Hazardous Weather Testbed (HWT) 2007 Spring Experiment, for a domain covering the eastern 2/3 of the continental U.S. This pilot system consists of ten hybrid perturbation members that consist of a combination of perturbed initial conditions and various microphysics and PBL physics parameterization schemes. The design considerations and the scientific questions that the system intends to address will be presented and discussed.

In addition to traditional ensemble products widely used in large-scale and mesoscale ensemble forecasting systems, such as the mean, spread, and probability of selected forecast fields, emphases are given to the generation and assessment of products specific to storm-scale, cloud-resolving ensemble forecasts. Such products include but are not limited to: probability of storm type (e.g., linear vs. cellular), large hail probability, icing potential (high super-cooled water content probability), damaging wind gusts at surface, reflectivity exceedance, updraft rotation, and supercell thunderstorm detection in the form of probability or joint probability for Supercell Composite Parameter, Significant Tornado Parameter, Supercell Detection Index, and Updraft Helicity. Many of these products are created in real time through existing capabilities in the SPC version of the N-AWIPS system for the use and evaluation by researchers and operational forecasters during the experiment. The statistical consistency of the ensemble system, in terms of spread-error relation, is assessed using the two-months of data after the experiment. The performance of the ensemble forecasts, in terms of quantitative skill scores, is compared with the NCEP operational SREF and 12 km NAM forecasts, and a CAPS 2-km WRF forecast over the same domain and period. Skill scores for sub-groups of the ensemble will be examined to assess the effectiveness of initial condition and physics perturbations.

Available online at ://http://ams.confex.com/ams/pdfpapers/124667.pdf.

Koracin, D., J. Businger, C. Dorman, J. Lewis, 2005: Formation, evolution, and dissipation of coastal sea fog. Bound.-Layer Meteorol., 117, 447-478.

Koracin, D., D. Leipper, J. Lewis, 2005: Modeling sea fog on the U. S. California coast during a hot spell event. Geofizika, 22, 59-82.

Koracin, D., J. Businger, C. Dorman, J. Lewis, 2005: Formation, evolution, and dissipation of coastal sea fog. Bound. - Layer Meteorol., 117, 447-478.

Koracin, D., D. Liepper, J. Lewis, 2005: Modeling sea fog on the U. S. California coast during a hot spell event. Geofizika, 22, 59-82.

Kuhlman, K. M., C. L. Ziegler, E. R. Mansell, D. R. MacGorman, J. M. Straka, 2006: Numerically Simulated Electrification and Lightning of the 29 June 2000 STEPS Supercell Storm. Monthly Weather Review, 134, 2734-2757.

A three-dimensional dynamic cloud model incorporating airflow dynamics, microphysics, and thunderstorm electrification mechanisms is used to simulate the first 3 h of the 29 June 2000 supercell from the Severe Thunderstorm Electrification and Precipitation Study (STEPS). The 29 June storm produced large flash rates, predominately positive cloud-to-ground lightning, large hail, and an F1 tornado. Four different simulations of the storm are made, each one using a different noninductive (NI) charging parameterization. The charge structure, and thus lightning polarity, of the simulated storm is sensitive to the treatment of cloud water dependence in the different NI charging schemes. The results from the simulations are compared with observations from STEPS, including balloon-borne electric field meter soundings and flash locations from the Lightning Mapping Array. For two of the parameterizations, the observed “inverted” tripolar charge structure is well approximated by the model. The polarity of the ground flashes is opposite that of the lowest charge region of the inverted tripole in both the observed storm and the simulations. Total flash rate is well correlated with graupel volume, updraft volume, and updraft mass flux. However, there is little correlation between total flash rate and maximum updraft speed. Based on the correlations found in both the observed and simulated storm, the total flash rate appears to be most representative of overall storm intensity.

Available online at ://http://www.ametsoc.org.

Kuhlman, K., D. MacGorman, M. Biggerstaff, W. D. Rust, T. Schuur, C. Ziegler, P. Krehbiel, 2006: Lightning and radar observatons of the 29 May 2004 supercell during TELEX. Preprints, 2nd Conference on Meteorological Applications of Lightning Data, Atlanta, GA, USA, American Meteorological Society, 3.3.

Kuhlman, K. M., E. R. Mansell, C. L. Ziegler, M. I. Biggerstaff, D. R. MacGorman, D. C. Dowell, 2008: EnKF data assimilation and dual-Doppler analysis of the 29 May 2004 Geary, Oklahoma supercell. Proc. 24th Conference on Severe Local Storms, Savannah, GA, USA, American Meteorological Society, P5.1.

On 29 May 2004, a long-track supercell storm moved across Oklahoma producing multiple tornadoes and numerous reports of large hail. Two mobile, C-band, Doppler (SMART-R) radars collected data in 2.5 min volume scans almost continuously for more than three hours. Dual-Doppler analyses were completed for select times using a1 km grid spacing and a 2-pass Barnes objective analysis in the interpolation of radial velocities and reflectivity to a Cartesian grid following Majcen et al (2008).

The focus of the radar data assimilation for this study is to retrieve the state of the storm rather than to develop forecast applications. For this purpose, the ensemble Kalman filter (EnKF) technique is used to assimilate reflectivity and/or radial velocity data into the model from SMART radar at approximately five minute intervals. Comparisons of the simulations employing EnKF to a simulation without data assimilation and to the dual-Doppler syntheses at various times of the storm's life-cycle will be presented. These results will be used to quantify the agreement between the simulation and the observations providing background such that future studies may use the simulations in order to to retrieve unobserved fields.

Available online at ://http://ams.confex.com/ams/24SLS/techprogram/paper_142031.htm.

Lewis, J., 2005: Roots of ensemble forecasting. Monthly Weather Review, 133, 1865-1885.

Lewis, J., R. Maddox, C. Crisp, 2006: Architect of sever storms forecasting: Colonel Robert C. Miller. Bulletin of the American Meteorological Society, 87, .

Lewis, J. M., 2007: Use of a mixed-layer model to investigate problems in operational prediction of return flow. Monthly Weather Review, 135, 2610-2628.

Lewis, J. M., 2007: A Forecaster's Story: Robert H. Johns. Electronic Journal of Severe Storm Meteorology, 2, 1-19.

The stages in the life of a severe storms forecaster, Robert H. Johns, are reconstructed from information in a series of interviews with him. The traditional interview format, question-and-answer mode, has been converted to a first-person narrative that leads to a more-continuous train of thought.
The storyline begins by describing Johns’ entrainment into meteorology as a youngster. By virtue of his contact and conversations with farmers in rural Indiana, he became interested in weather’s impact on the farmers and their crop yields. Early stimulation also came from a challenging weather project in the 6th grade and reading George Stewart’s novel Storm. From these experiences, Bob Johns decided to pursue a science career in service to society. This service took the form of work as a weather forecaster for the United States Weather Bureau (USWB)/National Weather Service (NWS).
The arduous path to severe storms forecaster is traced by highlighting his youthful experiences, his academic training, and the stepwise progression from student trainee to lead forecaster at the Severe Local Storms (SELS) unit of the USWB/NWS.

Available online at ://http://http://ejssm.org/ojs/index.php/ejssm/article/view/29/32.

Lewis, J. M., S. Lakshmivarahan, 2008: Sasaki's Pivotal Contribution: Calculus of Variations Applied to Weather Map Analysis. Monthly Weather Review, 136, 3553-3567.

Yoshikazu Sasaki developed a variational method of data assimilation, a cornerstone of modern-day analysis and prediction in meteorology. Fundamentally, he formulated data assimilation as a constrained minimization problem with equality constraints. The generation of this idea is tracked by analyzing his education and research at the University of Tokyo in the immediate post-WWII period. Despite austere circumstances — including limited financial support for education, poor living conditions, and a lack of educational resources — Sasaki was highly motivated and overcame these obstacles on his path to developing this innovative method of weather map analysis. We follow the stages of his intellectual development where information comes from access to his early publications, oral histories, and letters of reminiscence.
It has been argued that Sasaki’s unique contribution to meteorological data assimilation stems from his deterministic view of the problem – a view founded on the principles of variational mechanics. Sasaki’s approach to the problem is compared and contrasted with the stochastic view that was pioneered by Arnt Eliassen. Both of these optimal approaches are viewed in the context of the pragmatic/operational objective analysis schemes that were developed in the 1950s – 1960s. Finally, current-day methods, 3D-Var and 4D-Var, are linked to the optimal methods of Eliassen and Sasaki.

Lewis, J. M., 2008: Book Review: The Emergence of Numerical Weather Prediction: Richardson's Dream. Bulletin of the American Meteorological Society, 89, 1178-1179.

Lewis, J. M., S. Lakshmivarahan, S. Dhall, 2006: Dynamic Data Assimilation: A Least Squares Approach. Cambridge University Press, 654 pp.

NOAA Outstanding Publication Award in 2006

Lewis, J., 2008: Smagorinsky's GFDL; Building the team. Bulletin of the American Meteorological Society, 89, 1339-1353.

Joseph Smagorinsky (1924 - 2005) was a forceful and powerful figure in meteorology during the last half of the twentieth century. He served as director of the Geophysical Fluid Dynamics Laboratory (GFDL) for nearly thirty years (1955 - 1983); and during his tenure as director, this organization substantially contributed to advances in weather forecasting and climate diagnostics/prediction. The purpose of this research is to explore Smagorinsky’s philosophy of science and style of management that were central to the success of GFDL. Information comes from his early scientific publications, personal letters and notes in the possession of his family, several oral histories, and letters of reminiscence from scientists who worked within and outside GFDL.
The principal results of the study are: (1) early inspiration and development of Smagorinsky’s scientific philosophy came from his contact with Jule Charney and Harry Wexler, (2) his doctoral dissertation ideally prepared him for appointment as director of the U. S. Weather Bureau’s long-range numerical prediction project in 1955 — the General Circulation Research Section [later renamed GFDL], (3) he masterfully assembled a team of researchers to attack the challenging problem of general circulation modeling, and (4) he exhibited an authoritarian style of rule tempered by protection of the scientists from disrupting outside influence while celebrating the elitism and esprit de corps that characterized the laboratory.
A list of Smagorinsky’s management principles is found in the Appendix. Several of these tenets have been interspersed in the main body of the paper in support of actions he took at GFDL.

Liang, X. Z., M. XU, K. E. Kunkel, G. A. Grell, J. S. Kain, 2007: Regional Climate Model Simulation of U.S.–Mexico Summer Precipitation Using the Optimal Ensemble of Two Cumulus Parameterizations. Journal of Climate, 20, 5201-5207.

Liu, S., C. Qiu, Q. Xu, P. Zhang, J. Gao, A. Shao, 2005: An improved method for Doppler wind and thermodynamic retrievals. Advances in Atmospheric Sciences, 22, 90-102.

Liu, S., Q. Xu, P. Zhang, 2005: Quality control of Doppler velocities contaminated by migrating birds. Part II: Bayes identification and probability tests. Journal of Atmospheric and Oceanic Technology, 22, 1114-1121.

Liu, L., P. Zhang, Q. Xu, F. Kong, S. Liu, 2005: Retrieval model of dual linear polarization radar observations from simulation model output. Adv. Atmos. Sci. 22, 711-719., 22, 711-719.

Liu, S., M. Xue, Q. Xu, 2007: Using wavelet analysis to detect tornadoes from doppler radar radial-velocity observations. Journal of Atmospheric and Oceanic Technology, 24, 344-359.

MacGorman, D., D. Rust, T. Schuur, M. Biggerstaff, J. Straka, C. Ziegler, E. Mansell, P. Krehbiel, W. Rison, T. Hamlin, L. Carey, E. Bruning, K. Kuhlman, N. Ramig, C. Payne, 2005: Lightning Relative to Storm Structure and Microphysics in TELEX. Polarimetric radar and electrical structure of a multicell storm. Preprints, 32nd Conference on Radar Meteorology, Albuquerque, NM, USA, American Meteorological Society, CD-ROM, 10R.7.

MacGorman, D., C. L. Ziegler, E. Mansell, W. Beasley, B. Fiedler, 2005: Retrieval and assimilation of storm characteristics from both in-cloud and cloud-to-ground lightning data to improve mesoscale model forecasts. Final report to the Office of Naval Research (ONR Grant # N00014-00-1-0525) 1, 54 pp.

MacGorman, D. R., W. D. Rust, T. J. Schuur, M. I. Biggerstaff, J. M. Straka, C. L. Ziegler, E. R. Mansell, E. C. Bruning, K. M. Kuhlman, N. R. Lund, N. S. Biermann, C. Payne, L. D. Carey, P. R. Krehbiel, W. Rison, K. B. Eack, W. H. Beasley, 2008: TELEX: The Thunderstorm Electrification and Lightning Experiment. Bulletin of the American Meteorological Society, 89, 997-1013.

The field program of the Thunderstorm Electrification and Lightning Experiment (TELEX) took place in central Oklahoma, May–June 2003 and 2004. It aimed to improve understanding of the interrelationships among microphysics, kinematics, electrification, and lightning in a broad spectrum of storms, particularly squall lines and storms whose electrical structure is inverted from the usual vertical polarity. The field program was built around two permanent facilities: the KOUN polarimetric radar and the Oklahoma Lightning Mapping Array. In addition, balloon-borne electric-field meters and radiosondes were launched together from a mobile laboratory to measure electric fields, winds, and standard thermodynamic parameters inside storms. In 2004, two mobile C-band Doppler radars provided high-resolution coordinated volume scans, and another mobile facility provided the environmental soundings required for modeling studies. Data were obtained from twenty-two storm episodes, including several small isolated thunderstorms, mesoscale convective systems, and supercell storms. Examples are presented from three storms. A heavy-precipitation supercell storm on 29 May 2004 produced greater than 3 flashes per second for 1.5 h. Holes in the lightning density formed and dissipated sequentially in the very strong updraft and bounded weak echo region of the mesocyclone. In a small squall line on 19 June 2004, most lightning flashes in the stratiform region were initiated in or near strong updrafts in the convective line and involved positive charge in the upper part of the radar bright band. In a small thunderstorm on 29 June 2004, lightning activity began as polarimetric signatures of graupel first appeared near lightning initiation regions.

Available online at ://http://ams.allenpress.com/archive/1520-0477/89/7/pdf/i1520-0477-89-7-997.pdf.

MacGorman, D. R., T. Mansell, C. Ziegler, J. Straka, 2008: Detailed storm simulations by a numerical cloud model with electrification and lightning parameterizations. Preprints, 20th International Lightning Detection Conference, Tucson, AZ, USA, Vaisala, 28.

We have further developed our three-dimensional cloud model, which includes parameterizations of lightning, corona from ground, ion production and capture, and inductive and noninductive electrification mechanisms, as well as advanced treatments of advection, microphysics, and dynamics. Our most recent improvements have been to improve the model's treatment of microphysics, particularly particle size distributions. This model has been used to simulate many types of storms, from small isolated storms to extensive storm systems, supercell storms, and an idealized hurricane, with excellent similitude to observed kinematic structure in many cases. We will show examples of our simulations and will discuss relationships among the model fields, particularly between lightning and other storm properties. Lightning usually is correlated with precipitation ice mass and with the mass flux through the mixed phase region for updrafts >10 m/s.

MacGorman, D., C. Ziegler, T. Mansell, J. Straka, P. Krehbiel, B. Rison, T. Hamlin, 2005: Applications of advanced lightning mapping technologies to storm research and weather operations. Preprints, Conference on Meteorological Applications of Lightning Data, San Diego, CA, USA, American Meteorological Society, 2.1.

MacGorman, D. R., W. D. Rust, C. L. Ziegler, T. J. Schuur, E. R. Mansell, M. I. Biggerstaff, J. M. Straka, E. C. Bruning, K. M. Kuhlman, N. R. Ramig, C. D. Payne, N. S. Biermann, P. R. Krehbiel, W. Rison, T. Hamlin, L. D. Carey, 2005: Lightning relative to storm structure, evolution, and microphysics in TELEX. Preprints, 32nd Conference on Radar Meteorology, Albuquerque, NM, USA, American Meteorological Society, 10R.7.

Mansell, E. R., D. R. MacGorman, C. L. Ziegler, J. M. Straka, 2005: Charge structure in a simulated multicell thunderstorm. Journal of Geophysical Research, 110, .

A three-dimensional dynamic cloud model is used to investigate electrification of the full life cycle of an idealized continental multicell storm. Five laboratory-based parameterizations of noninductive graupel-ice charge separation are compared. Inductive (i.e., electric field-dependent) charge separation is tested for rebounding graupel-droplet collisions. Each noninductive graupel-ice parameterization is combined with variations in the effectiveness of inductive charging (off, moderate, and strong) and in the minimum ice crystal concentration (10 or 50/L). Small atmospheric ion processes such as hydrometeor attachment and point discharge at the ground are treated explicitly. Three of the noninductive schemes readily produced a normal polarity charge structure, consisting of a main negative charge region with an upper main positive charge region and a lower positive charge region. Negative polarity cloud-to-ground (CG) flashes occurred when the lower positive charge (LPC) region had sufficient charge density to cause high electric fields. Two of the three also produced one or more +CG flashes. The other two noninductive charging schemes, which are dependent on the graupel rime accretion rate, tended to produce an initially inverted polarity charge structure and +CG flashes. The model results suggest that inductive graupel-droplet charge separation could play a role in the development of lower charge regions. Noninductive charging, on the other hand, was also found to be capable of producing strong lower charge regions in the tests with a minimum ice crystal concentration of 50/L.

Mansell, T., C. Ziegler, D. MacGorman, 2006: A Lightning Data Assimilation Technique for Mesoscale Forecast Models. Preprints, 1st International Lightning Meteorology Conference, Tucson, AZ, USA, Vaisala, CD-ROM, N/A. [Available from Vaisala, Inc., Tucson Operations, 2705 E. Medina Rd., Tucson, AZ, USA, 85706.]

Lightning observations have been assimilated into the COAMPS mesoscale model for improvement of forecast initial conditions. Data are used from the National Lightning Detection Network (NLDN, cloud-to-ground lightning detection) and a Lightning Mapping Array (LMA; total lightning detection) that was installed in western Kansas/eastern Colorado. The assimilation method uses lightning as a proxy for the presence or absence of deep convection. During assimilation, lightning data are used to control the Kain-Fritsch (KF) convection parameterization scheme (CPS). The KF scheme can be forced to try to produce convection where lightning indicated storms, and, conversely, can optionally be prevented from producing spurious convection where no lightning was observed. Up to 1 g/kg of water vapor may be added to the boundary layer when the KF convection is too weak. The method does not make any use lightning-rainfall relationships, rather allowing the KF scheme to generate heating and cooling rates from its modeled convection. The method could therefore be used easily for real-time assimilation of any source of lightning observations.

Results will be presented for a warm-season test case 20-21 July 2000, when storms initiated and developed in large systems in Kansas both days. The second round of convection began by 22:00 UTC (20 July), and storm system with strong outflow had developed by 00 UTC on 21 July. Lightning data were assimilated over a 24 hour period (starting at 00 UTC on 20 July), covering the first round of convection and the start of the second. A control run was spun up over the same period only with the usual 12-hourly update cycle. As expected, during the assimilation period the model produces substantially more accurate precipitation (rates and location) than the control forecast. Even when water vapor was added to enhance convection, the rainfall rates were generally less than those indicated by rain gauge data. A forecast was started from the resulting initial condition at 00 UTC on 21 July 2000.

The lightning assimilation was successful in generating the cold pool that was present in the surface observations at initialization of the forecast. The resulting forecast showed considerably more skill than the control forecast, especially in the first few hours as convection was triggered by the propagation of the cold pool boundary.

Mansell, E. R., C. L. Ziegler, D. R. MacGorman, 2006: A Lightning Data Assimilation Technique for Mesoscale Forecast Models. Preprints, Second Conference on Meteorological Applications of Lightning Data, Atlanta, GA, USA, American Meteorological Society, 4.2.

Lightning observations have been assimilated into the COAMPS mesoscale model for improvement of forecast initial conditions. Data are used from the National Lightning Detection Network (NLDN, cloud-to-ground lightning detection) and a Lightning Mapping Array (LMA; total lightning detection) that was installed in western Kansas/eastern Colorado. The assimilation method uses lightning as a proxy for the presence or absence of deep convection. During assimilation, lightning data are used to control the Kain-Fritsch (KF) convection parameterization scheme (CPS). The KF scheme can be forced to try to produce convection where lightning indicated storms, and, conversely, can optionally be prevented from producing spurious convection where no lightning was observed. Up to 1 g/kg of water vapor may be added to the boundary layer when the KF convection is too weak. The method does not make any use lightning-rainfall relationships, rather allowing the KF scheme to generate heating and cooling rates from its modeled convection. The method could therefore be used easily for real-time assimilation of any source of lightning observations.

Results will be presented for a warm-season test case 20-21 July 2000, when storms initiated and developed in large systems in Kansas both days. The second round of convection began by 22:00 UTC (20 July), and storm system with strong outflow had developed by 00 UTC on 21 July. Lightning data were assimilated over a 24 hour period (starting at 00 UTC on 20 July), covering the first round of convection and the start of the second. A control run was spun up over the same period only with the usual 12-hourly update cycle. As expected, during the assimilation period the model produces substantially more accurate precipitation (rates and location) than the control forecast. Even when water vapor was added to enhance convection, the rainfall rates were generally less than those indicated by rain gauge data. A forecast was started from the resulting initial condition at 00 UTC on 21 July 2000.

The lightning assimilation was successful in generating the cold pool that was present in the surface observations at initialization of the forecast. The resulting forecast showed considerably more skill than the control forecast, especially in the first few hours as convection was triggered by the propagation of the cold pool boundary.

Available online at ://http://ams.confex.com/ams/Annual2006/techprogram/paper_104180.htm.

Mansell, E. R., C. L. Ziegler, D. R. MacGorman, 2007: A Lightning Data Assimilation Technique for Mesoscale Forecast Models. Monthly Weather Review, 135, 1732-1748.

Lightning observations have been assimilated into a mesoscale model for improvement of forecast initial conditions. Data are used from the National Lightning Detection Network (cloud-to-ground lightning detection) and a Lightning Mapping Array (total lightning detection) that was installed in western Kansas–eastern Colorado. The assimilation method uses lightning as a proxy for the presence or absence of deep convection. During assimilation, lightning data are used to control the Kain–Fritsch (KF) convection parameterization scheme. The KF scheme can be forced to try to produce convection where lightning indicated storms, and, conversely, can optionally be prevented from producing spurious convection where no lightning was observed. Up to 1 g/kg of water vapor may be added to the boundary layer when the KF convection is too weak. The method does not employ any lightning–rainfall relationships, but rather allows the KF scheme to generate heating and cooling rates from its modeled convection. The method could therefore easily be used for real-time assimilation of any source of lightning observations. For the case study, the lightning assimilation was successful in generating cold pools that were present in the surface observations at initialization of the forecast. The resulting forecast showed considerably more skill than the control forecast, especially in the first few hours as convection was triggered by the propagation of the cold pool boundary.

Mansell, E., C. L. Ziegler, E. Bruning, 2007: Simulated electrification of a TELEX multicell storm. Preprints, 13th International Conference on Atmospheric Electricity, Beijing, China, International Commission on Atmospheric Electricity, 290-293.

McPherson, R. A., D. J. Stensrud, 2005: Influences of a winter wheat belt on the evolution of the boundary layer. Monthly Weather Review, 133, 2178-2199.

Evidence exists that a large-scale alteration of land use by humans can cause changes in the climatology of the region. The largest-scale transformation is the substitution of native landscape by agricultural cropland. This modeling study examines the impact of a direct substitution of one type of grassland for another - in this case, the replacement of tallgrass prairie with winter wheat. The primary difference between these grasses is their growing season: native prairie grasses of the U. S. Great Plains are warm-season grasses whereas winter wheat is a cool-season grass.

Case study simulations were conducted for 27 March 2000 and 5 April 2000 - days analyzed in previous observational studies. The simulations provided additional insight into the physical processes involved and changes that occurred throughout the depth of the planetary boundary layer. Results indicate the following: 1) with the proper adjustment of vegetation parameters, land-use type, fractional vegetation coverage, and soil moisture, the numerical simulations were able to capture the overall patterns measured near the surface across a growing wheat belt during benign springtime conditions in Oklahoma; 2) the impacts of the mesoscale belt of growing wheat included increased values of latent heat flux and decreased values of sensible heat flux over the wheat, increased values of atmospheric moisture near the surface above and downstream of the wheat, and a shallower planetary boundary layer (PBL) above and downstream of the wheat; 3) in the sheared environments that were examined, a shallower PBL that resulted from growing wheat (rather than natural vegetation) led to reduced entrainment of higher momentum air into the PBL and, thus, weaker winds within the PBL over and downwind from the growing wheat; 4) for the cases studied, gradients in sensible heat were insufficient to establish an unambiguous vegetation breeze or its corresponding mesoscale circulation; 5) the initialization of soil moisture within the root zone aided latent heat fluxes from growing vegetation; and 6) reasonable specification of land surface parametes was required for the correct simulation and prediction of surface heat fluxes and resulting boundary layer development.

Pinto, J., C. Kessinger, B. Hendrickson, D. Megenhardt, P. Harasti, Q. Xu, P. Zhang, Q. Zhao, M. Frost, J. Cook, S. Potts, 2007: Storm characterization and short term forecasting potential using a phase array radar. Extended Abstracts, 33rd Conference on Radar Meteorology. 6–10 August 2007, Cairns, Australia. Amer. Meteor. Soc.,, Cairns, Australia, Amer. Meteor. Soc., P5.18.

Available online at ://http://ams.confex.com/ams/pdfpapers/123703.pdf.

Qiu, C., A. Shao, S. Liu, Q. Xu, 2005: A two-step variational method for three-dimensional wind retrieval from single Doppler radar. Meteorology and Atmospheric Physics, 90(1-2), .

Qiu, C., A. Shao, Q. Xu, L. Wei, 2007: An Ensemble-Based 4DVar Approach Based on SVD Technique. Extended Abstracts, 18th Conference on Numerical Weather Prediction, park City, UT, USA, Amer. Meteor. Soc., P2.2.

Available online at ://http://ams.confex.com/ams/22WAF18NWP/techprogram/paper_123933.htm.

Qiu, C., A. Shao, Q. Xu, L. Wei, 2007: Fitting model fields to observations by using singular value decomposition – An ensemble-based 4DVar approach. Journal of Geophysical Research - D: Atmospheres., 112, .

Segele, Z. T., D. J. Stensrud, I. C. Ratcliffe, G. M. Henebry, 2005: Influence of a hailstreak on boundary layer evolution. Monthly Weather Review, 133, 942-960.

Severe thunderstorms developed on 20 June 1997 and produced heavy precipitation, damaging winds, and large hail over two swaths in southeastern South Dakota. Calculations of fractional vegetation coverage (scaled from 0 to 1) based upon composite satellite data indicate that, within the hailstreak region, vegetation coverage decreased from 0.50 to near 0.25 owing to the damaging effects of hail on the growing vegetation. The northern edge of the larger hailstreak was located a few km south of Chamberlain, South Dakota, a National Weather Service surface observation site. Hourly observations from Chamberlain and several nearby surface sites in South Dakota are averaged over 7 days both before and after this hail event. These observations illustrate that the late afternoon (nighttime) temperatures are 2°C higher (2°C lower) near the hailstreak after the event than before the event. Similarly, daily average dewpoint temperatures after the event are 2.6°C lower near the hailstreak. These changes are consistent with the influences of a recently devegetated zone on changes to the surface energy budget.

To explore how these hailstreaks further affected the evolution of the planetary boundary layer in this region, two model simulations are performed using the Fifth-Generation Pennsylvania State University-National Center for Atmospheric Research Mesoscale Model (MM5). In the control run, climatology is used for the land surface characteristics and hence the simulation is independent of the hailstreaks. In the hailstreak simulation (HSS), the fractional vegetation coverage and soil moisture in the hailstreak regions are modified to reflect the likely conditions within the hailstreaks. Two different days are simulated, one with low surface wind speeds and one with stronger surface wind speeds. For the low surface wind speed case, the HSS simulation produces a sea-breeze-like circulation in the boundary layer by mid-morning. For the stronger surface wind speed case, this sea-breeze-like circulation does not develop in the HSS, but the simulated low-level temperatures are modified over a larger area. These results suggest that to capture and reasonably simulate the evolution of boundary layer structures, there is a need for routine daily updates of land surface information. Hailstreaks also are important to consider in the future as the focus for observational studies on non-classical mesoscale circulations.

Stensrud, D. J., 2007: Parameterization Schemes: Keys to Understanding Numerical Weather Prediction Models. Cambridge University Press, 459 pp.

2008 Office of Oceanic and Atmospheric Research (OAR) Outstanding Scientific Paper Award - Special Recognition

Numerical weather prediction models play an increasingly important role in meteorology, both in short- and medium-range forecasting and global climate change studies. Arguably, the most important components of any numerical weather prediction model are the subgrid-scale parameterization schemes. These parameterization schemes determine the amount of energy that reaches the Earth's surface; determine the evolution of the planetary boundary layer; decide when subgrid-scale clouds and convection develop and produce rainfall; and determine the influence of subgrid-scale orography on the atmosphere. The analysis and understanding of parameterization schemes is a key aspect of numerical weather prediction.

This is the first book to provide in-depth explorations of the most commonly used types of parameterization schemes that influence short-range weather forecasts and global climate models. Each chapter covers a different type of parameterization scheme, starting with an overview explaining why each scheme is needed, and then reviewing the basic theory behind it. Several parameterizations are summarized and compared, followed by a discussion of their limitations. Review questions at the end of each chapter enable readers to monitor their understanding of the topics covered, and solutions are available at www.cambridge.org/9780521865401.

Stensrud, D. J., N. Yussouf, 2005: Bias-corrected short-range ensemble forecasts of near surface variables. Meteorological Applications, 12, 217-230.

A multimodel short-range ensemble forecasting system created as part of a National Oceanic and Atmospheric Administration program on improved high temperature forecasting during the summer of 2003 is evaluated. Results from this short-range ensemble system indicate that using the past complete 12 days of forecasts to bias correct today’s forecast yields ensemble mean forecasts of 2-m temperature, 2-m dewpoint temperature, and 10-m wind speed that are competitive with or better than those available from any of the model output statistics presently generated operationally in the United States. However, the bias-corrected ensemble system provides more than just the ensemble mean forecast. Probabilities produced by this system are skillful and reliable, and have been found to be valuable when evaluated in a cost-loss model. The ensemble appears to provide better guidance for more unlikely events, such as very warm temperatures, that likely have the greatest economic significance. Industries that are sensitive to the weather, such as power companies, transportation, and agriculture, may benefit from the probability information provided. Thus, it is possible to develop post-processing for short-range ensemble forecasting systems that is competitive with or better than traditional post-processing techniques, thereby allowing the rapid production of useful and accurate guidance forecasts of many near surface variables.

Stensrud, D. J., M. C. Coniglio, R. P. Davies-Jones, J. S. Evans, 2005: Comments on “A Theory for Strong Long-Lived Squall Lines” Revisited. Journal of the Atmospheric Sciences, 62, 2989-2996.

No abstract.

Stensrud, D. J., H. E. Brooks, 2005: The future of peer review?. Weather and Forecasting, 20, 825-826.

No abstract.

Stensrud, D. J., 2006: NEHRTP Workshop: Improving weather forecast services used by the electric utility industry. Bulletin of the American Meteorological Society, 87, 499-501.

No abstract.

Stensrud, D. J., N. Yussouf, M. E. Baldwin, J. T. McQueen, J. Du, B. Zhou, B. Ferrier, G. Manikin, F. M. Ralph, J. M. Wilczak, A. B. White, I. Djlalova, J. W. Bao, R. J. Zamora, S. G. Benjamin, P. A. Miller, T. L. Smith, T. Smirnova, M. F. Barth, 2006: The New England High-Resolution Temperature Program. Bulletin of the American Meteorological Society, 87, 491-498.

The New England High-Resolution Temperature Program seeks to improve the accuracy of summertime 2-m temperature and dewpoint temperature forecasts in the New England region through a collaborative effort between the research and operational components of the National Oceanic and Atmospheric Administration (NOAA). The four main components of this program are 1) improved surface and boundary layer observations for model initialization, 2) special observations for the assessment and improvement of model physical process parameterization schemes, 3) using model forecast ensemble data to improve upon the operational forecasts for near surface variables, and 4) transfering knowledge gained to commercial weather services and end users. Since 2002 this program has enhanced surface temperature observations by adding 70 new automated Cooperative Observer Program (COOP) sites, identified and collected data from over 1000 non-NOAA mesonet sites, and deployed boundary layer profilers and other special instrumentation throughout the New England region to better observe the surface energy budget. Comparisons of these special data sets with numerical model forecasts indicate that near surface temperature errors are strongly correlated to errors in the model predicted radiation fields. The attenuation of solar radiation by aerosols is one potential source of the model radiation bias. However, even with these model errors, results from bias-corrected ensemble forecasts are more accurate than the operational model output statistics (MOS) forecasts for 2-m temperature and dewpoint temperature, while also providing reliable forecast probabilities. Discussions with commerical weather vendors and end users have emphasized the potential economic value of these probabilistic ensemble-generated forecasts.

Stensrud, D. J., N. Yussouf, 2007: Reliable probabilistic quantitative precipitation forecasts from a short-range ensemble forecasting system. Weather and Forecasting, 22, 3-17.

A simple binning technique is developed to produce reliable 3-h probabilistic quantitative precipitation forecasts (PQPFs) from the National Centers for Environmental Prediction (NCEP) multimodel shortrange ensemble forecasting system obtained during the summer of 2004. The past 12 days’ worth of forecast 3-h accumulated precipitation amounts and observed 3-h accumulated precipitation amounts from the NCEP stage-II multisensor analyses are used to adjust today’s 3-h precipitation forecasts. These adjustments are done individually to each of ensemble members for the 95 days studied. Performance of the adjusted ensemble precipitation forecasts is compared with the raw (original) ensemble predictions. Results show that the simple binning technique provides significantly more skillful and reliable PQPFs of rainfall events than the raw forecast probabilities. This is true for the base 3-h accumulation period as well as for accumulation periods up to 48 h. Brier skill scores and the area under the relative operating characteristics curve also indicate that this technique yields skillful probabilistic forecasts. The performance of the adjusted forecasts also progressively improves with the increased accumulation period. In addition, the adjusted ensemble mean QPFs are very similar to the raw ensemble mean QPFs, suggesting that the method does not significantly alter the ensemble mean forecast. Therefore, this simple postprocessing scheme is very promising as a method to provide reliable PQPFs for rainfall events without degrading the ensemble mean forecast.

Straka, J. M., E. R. Mansell, 2005: A bulk microphysics parameterization with multiple ice precipitation categories. Journal of Applied Meteorology, 44, 445-466.

Straka, J., E. Mansell, D. MacGorman, E. Bruning, C. L. Ziegler, 2007: Comparison of modeled and observed electrical charging and lightning in a low-precipitation supercell storm during TELEX. Preprints, 13th International Conference on Atmospheric Electricity, Beijing, China, International Commission on Atmospheric Electricity, 272-275.

Taylor, A. A., L. M. Leslie, D. J. Stensrud, 2005: Forecasts of near-surface variables using a coupled atmosphere-land surface model. 19th Conference on Hydrology, San Diego, CA, USA, American Meteorological Society, 1.6.

Thompson, W., S. Burk, J. Lewis, 2005: Fog and low clouds in a coastally trapped disturbance. J. Geophysical Research, 110, .

Thompson, W., S. Burk, J. Lewis, 2005: Fog and low clouds in a coastally trapped disturbance. Journal of Geophysical Research - D: Atmospheres, 110, .

Trapp, R. J., S. A. Tessendorf, E. S. Godfrey, H. E. Brooks, 2005: Tornadoes from Squall Lines and Bow Echoes. Part I: Climatological Distribution. Weather and Forecasting, 20, 23-34.

The primary objective of this study was to estimate the percentage of U.S. tornadoes that are spawned annually by squall lines and bow echoes, or quasi-linear convective systems (QLCSs). This was achieved by examining radar reflectivity images for every tornado event recorded during 1998-2000 in the contiguous United States. Based on these images, the type of storm associated with each tornado was classified as cell, QLCS, or other. Of the 3828 tornadoes in the database, 79% were produced by cells, 18% were produced by QLCSs, and the remaining 3% were produced by other storm types, primarily rainbands of landfallen tropical cyclones. Geographically, these percentages as well as those based on tornado days exhibited wide variations. For example, 50% of the tornado days in Indiana were associated with QLCSs. In an examination of other tornado attributes, statistically more weak (F1) and fewer strong (F2-F3) tornadoes were associated with QLCSs than with cells. QLCS tornadoes were more probable during the winter months than were cells. And finally, QLCS tornadoes displayed a comparatively higher and statistically significant tendency to occur during the late night/early morning hours. Further analysis revealed a disproportional decrease in F0-F1 events during this time of day, which led the authors to propose that many (perhaps as many as 12% of the total) weak QLCSs tornadoes were not reported.

Wandishin, M. S., M. E. Baldwin, S. L. Mullen, J. V. Cortinas, 2005: Short-range ensemble forecasts of precipitation type. Weather and Forecasting, 20, 609-626.

Wandishin, M. S., D. J. Stensrud, S. L. Mullen, L. J. Wicker, 2008: On the Predictability of Mesoscale Convective Systems: Two-Dimensional Simulations. Weather and Forecasting, 23, 773-785.

Mesoscale convective systems (MCSs) are a dominant climatological feature of the central United States and are responsible for a substantial fraction of warm season rainfall. Yet very little is known about the predictability of MCSs. To help alleviate this situation, a series of ensemble simulations of an MCS are performed on a two-dimensional, storm-scale (dx ~ 1 km) model. Ensemble member perturbations in wind speed, relative humidity, and instability are based on current 24-h forecast errors from the North American
Model (NAM). The ensemble results thus provide an upper bound on the predictability of mesoscale convective systems within realistic estimates of environmental uncertainty, assuming successful convective initiation.

The simulations are assessed by considering an ensemble member a success when it reproduces a convective system of at least 20 km in length (roughly the size of two convective cells) within 100 km on either side of the location of the MCS in the control run. By that standard, MCSs occur roughly 70% of the time for perturbation magnitudes consistent with 24-h forecast errors. Reducing the perturbations for all fields to one-half the 24-h error values increases the MCS success rate to over 90%. The same improvement in
forecast accuracy would lead to a 30%–40% reduction in maximum surface wind speed uncertainty and a roughly 20% reduction in the uncertainty in maximum updraft strength, and initially slower growth in the
uncertainty in the size of the MCS. However, the occurrence of MCSs drops below 50% as the midlayer mean relative humidity falls below 65%. The response of the model to reductions in forecast errors for instability, moisture, and wind speed is not consistent and cannot be easily generalized, but each can have a substantial impact on forecast uncertainty.

Wang, B., J. Zhang, W. Xia, K. Howard, X. Xu, 2008: Analysis of radar and gauge rainfall during the warm season in Oklahoma. Preprints, The 22nd Conf. on Hydrology, New Orleans, LA, USA, Amer. Meteor. Soc., CD-ROM, P2.1.

Weiss, S. J., J. S. Kain, D. R. Bright, J. J. Levit, M. Pyle, Z. I. Janjic, B. Ferrier, J. Du, M. L. Weisman, M. Xue, 2007: The NOAA Hazardous Weather Testbed: Collaborative testing of ensemble and convection-allowing WRF models and subsequent transfer to operations at the Storm Prediction Center.. Preprints, 22th Conference on Weather Analysis and Forecasting/18th Conference on Numerical Weather Prediction, Park City, UT, USA, Amer. Meteor. Soc., CD-ROM, 6B.4.

Weiss, S. J., J. S. Kain, D. R. Bright, J. J. Levit, M. Pyle, Z. I. Janjic, B. S. Ferrier, J. Du, M. L. Weisman, M. Xue, 2007: The NOAA Hazardous Weather Testbed: Collaborative testing of ensemble and convection-allowing WRF models and subsequent transfer to operations at the Storm Prediction Center. Preprints, 22th Conference on Weather Analysis and Forecasting/18th Conference on Numerical Weather Prediction, Park City, UT, USA, Amer. Meteor. Soc., CD-ROM, Amer. Mete. [Available from S. J. Weiss, SPC, 120 David L. Boren Blvd, Norman, OK, USA, 73072.]

Since 2003, the Storm Prediction Center (SPC) has played a leading role in testing various configurations of Short-Range Ensemble Forecast (SREF) systems and high resolution WRF models for their operational utility. These test and evaluation activities have occurred during organized collaborative activities in the NOAA Hazardous Weather Testbed (HWT) in Norman. The HWT is designed to bring research scientists, model developers, and forecasters together to work on issues of mutual interest, facilitating the rapid transfer of research to operations. This organizational framework helps researchers and model developers to better understand the operational challenges and requirements of forecasters, educates forecasters on new science and technological advances, and has accelerated the application of new modeling approaches to severe weather forecasting. This paper focuses on the use of the operational NCEP SREF and two experimental high resolution convection-allowing WRF models as complementary sources of information for SPC forecasters.

NCEP is running a 21 member multi-model, multi-analysis SREF system with enhanced physics diversity four times daily with output through 87 hours. SPC processes the grids from all SREF members and produces a large variety of products for severe weather forecasting, including standard spaghetti, mean and spread, probability, and max/min charts, as well as specialized multi-parameter convective fields and post-processed calibrated probabilities for the occurrence of thunderstorms, dry thunderstorms, and severe thunderstorms.

NCEP has also been running an experimental high resolution WRF-Non-hydrostatic Mesoscale Model (WRF-NMM4) for the SPC since April 2004; this model was recently upgraded to a 4 km grid length. And starting in November 2006, SPC forecasters have had access to output from a 4 km Advanced Research WRF (WRF-ARW4) developed by NCAR and run at the National Severe Storms Laboratory. Both WRF models are initialized from a cold start once daily at 0000 UTC using initial and lateral boundary conditions from the operational North American Mesoscale model, and provide forecasts through a 36 hour period over a domain covering approximately three-fourths of the U.S. Several unique WRF products have been developed for use by severe weather forecasters, including simulated reflectivity and measures of updraft rotation in model-generated storms.

The incorporation of SREF and high resolution WRF guidance into an operational severe weather forecasting environment already dealing with high volumes of observational and model data requires careful assessment of the unique strengths of each modeling system, and knowledge of the specific needs of SPC forecasters. Since the SPC severe weather forecast mission focuses on phenomena smaller than that predicted by mesoscale models, such as tornadoes and severe thunderstorms, the traditional forecast methodology has focused on first predicting the evolution of the mesoscale environment and then determining the spectrum of convective storms a particular environment may support. SREF output has been found to be particularly useful in quantifying the likelihood that the environment will occupy specific parts of convective parameter space, as well as the likelihood and timing for thunderstorms and severe thunderstorms to develop over Outlook-scale regions. While this can be extremely helpful to SPC forecasters, more detailed information about the intensity and mode of storms is also needed, since the type of severe weather (e.g., tornadoes, damaging wind) is often strongly related to convective mode. The value of the high resolution WRF guidance is most evident here, as it has capability to resolve near storm-scale convective characteristics, such as the development of discrete cells ahead of a line of storms, and the development of model storms with rotating updrafts.

We will examine the complementary role of SREF and high resolution WRF output during several strongly-forced and weakly-forced severe weather days during the winter and spring severe weather period and illustrate the operational application of these model datasets in the SPC decision-making process for both Convective Outlooks and Watches.

Available online at ://http://ams.confex.com/ams/pdfpapers/124772.pdf.

Xu, Q., 2005: Non-modal growths of symmetric perturbations produced by paired normal modes. 32nd Conference on Radar Meteorology, Albuquerque, NM, USA, American Meteorological Society, CD-ROM, 6M4.

Xu, Q., K. Nai, L. Wei, P. Zhang, L. Wang, H. Lu, Qingyun Zhao, 2005: Progress in doppler radar data assimilation. 32nd Conference on Radar Meteorology, Albuquerque, NM, USA, American Meteorological Society, CD-ROM, JP1J7.

Xu, Q., W. Gu, S. Gao, 2005: Nonlinear oscillations of semigeostrophic Eady waves in the presence of diffusivity. Advances in Atmospheric Sciences, 22, 49-57.

Xu, Q., 2005: Representations of inverse covariances by differential operators. Advances in Atmospheric Sciences, 22, 181-198.

Xu, Q., L. Wei, H. Lu, K. Nai, Q. Zhao, 2006: Phased-array radar data assimilation at the National Weather Radar Testbed -- Theoretical issues and practical solutions. Preprints, Fourth European Conference on Radar Meteorology, Barcelona, Spain, ERAD multiple Sponsors. See http://www.grahi.upc.edu/ERAD2006/i, 515-518.

Available online at ://http://www.grahi.upc.edu/ERAD2006/index.php.

Xu, Q., S. Liu, M. Xue, 2006: Background error covariance functions for vector wind analyses using Doppler radar radial-velocity observations. Quart. J. Roy. Meteor. Soc., 132, 2887-2904.

Xu, Q., K. Nai, L. Wei, 2007: An innovation method for estimating radar radial-velocity observation error and background wind error covariances. Quart. J. Roy. Meteor. Soc., 133, 407-415.

Xu, Q., 2007: Measuring information content from observations for data assimilation: Relative entropy versus Shannon entropy difference. Tellus, 59A, 198-209.

Xu, Q., 2007: Modal and non-modal symmetric perturbations. Part 1. Modal solutions and partial orthogonality. Journal of the Atmospheric Sciences, 64, 1745-1763.

Xu, Q., T. Lei, S. Gao, 2007: Modal and non-modal symmetric perturbations. Part 2. Non-modal growths measured by total perturbation energy. Journal of the Atmospheric Sciences, 64, 1764-1781.

Xu, Q., K. Nai, L. Wei, H. Lu, P. Zhang, S. Liu, D. Parrish, 2007: Estimating radar wind observation error and NCEP WRF background wind error covariances from radar radial-velocity innovations. Extended Abstracts, 18th Conference on Numerical Weather Prediction, Park City, UT, USA, Amer. Meteor. Soc., 1B.3.

Available online at ://http://ams.confex.com/ams/pdfpapers/123419.pdf.

Xu, Q., L. Wei, H. Lu, Q. Zhao, C. Qiu, 2007: Time-expanded sampling for ensemble-based filter with covariance localization: assimilation experiments with a shallow-water equation model. Preprints, 18th Conference on Numerical Weather Prediction, Park City, UT, USA, Amer. Meteor. Soc., 6B.1A.

Available online at ://http://ams.confex.com/ams/pdfpapers/123409.pdf.

Xu, Q., H. Lu, L. Wei, Q. Zhao, 2007: Studies of phased-array scan strategies for radar data assimilation. Extended Abstracts, 33rd Conference on Radar Meteorology, Cairns, Australia, Amer. Meteor. Soc., 4A.3.

Available online at ://http://ams.confex.com/ams/pdfpapers/122972.pdf.

Xu, Q., L. Wei, H. Lu, C. Qiu, Q. Zhao, 2008: Time-expanded sampling for ensemble-based filters: Assimilation experiments with a shallow-water equation model. Journal of Geophysical Research - D: Atmospheres, 113, .

Xu, Q., H. Lu, L. Wei, S. Gao, M. Xue, M. Tong, 2008: Time-expanded sampling for ensemble Kalman filter: Assimilation experiments with simulated Radar observations. Monthly Weather Review, 136, 2651-2667.

Xu, X., K. Howard, J. Zhang, 2008: An Automated Radar Technique for the Identification of Tropical Precipitation. Journal of Hydrometeorology, x, xx-xx.

Xu, Q., L. Wei, S. Healy, 2009: Measuring information content from observations for data assimilations: connection between different measures and application to radar scan design. Tellus, 61A, 144-153.

The previously derived formulations for using the relative entropy and Shannon entropy difference to measure information content from observations are revisited in connection with another known information measure – degrees of freedom for signal, which is defined as the statistical average of the signal part of the relative entropy. For a linear assimilation system, the statistical average of the relative entropy reduces to the Shannon entropy difference. The formulations are extended for four-dimensional variational data assimilation (4DVar). The extended formulations reveal that the information content increases (or decreases) as the model error increase (or decrease) and/or become strongly (or weakly) correlated in 4D space. These properties are also highlighted by illustrative examples, and the extended formulations are shown to be potential useful for designing optimum phased-array radar scan configurations to maximize the extractable information contents from radar observations by a 4DVar analysis system.

Xue, M., F. Kong, D. Weber, K. W. Thomas, Y. Wang, K. Brewster, K. K. Droegemeier, J. S. Kain, S. J. Weiss, D. R. Bright, M. S. Wandishin, M. C. Coniglio, J. Du, 2007: CAPS realtime storm-scale ensemble and high-resolution forecasts as part of the NOAA Hazardous Weather Testbed 2007 Spring Experiment.. Preprints, 22th Conference on Weather Analysis and Forecasting/18th Conference on Numerical Weather Prediction, Park City, UT, USA, Amer. Meteor. Soc., CD-ROM, 3B.1.

Xue, M., F. Kong, D. B. Weber, K. W. Thomas, Y. Wang, K. Brewster, K. K. Droegemeier, J. S. Kain, S. J. Weiss, D. R. Bright, M. S. Wandishin, M. C. Coniglio, J. Du, 2007: CAPS realtime storm-scale ensemble and high-resolution forecasts as part of the NOAA Hazardous Weather Testbed 2007 Spring Experiment. Preprints, 22th Conference on Weather Analysis and Forecasting/18th Conference on Numerical Weather Prediction, Park City, UT, USA, Amer. Meteor. Soc., CD-ROM, 3B.1. [Available from Ming Xue, CAPS, 120 David L. Boren Blvd, Norman, OK, USA, 73072.]

As a continuation of past collaborations with the NOAA Hazardous Weather Testbed (HWT), the Center for Analysis and Prediction of Storms (CAPS) at the University of Oklahoma will produce daily 10-member 4-km-resolution ensemble forecasts during the spring of 2007, as contributions to the HWT 2007 Spring Experiment. At the same time, a single 2-km deterministic forecast will be produced over the same domain that covers two thirds of the continental US. The forecasts will start from 2100 UTC and extend to 0600 UTC of the third day for a total length of 33 hours. The experiment will start in mid-April and last for about 2 months.

The CAPS effort in 2007 will use the WRF ARW model and the ensemble will include both initial/boundary condition and physics perturbations. The initial and boundary condition perturbations will come from the NCEP 2100 UTC SREF forecast cycle, with the control-member initial condition coming from the NAM 2100 UTC analysis on the 12 km grid. The physics perturbation members are designed for easy identification of the strengths and weakness of leading microphysics and PBL schemes within WRF.

Selected data fields will be fed directly into the NAWIPS systems in the HWT for use by experimental forecast and evaluation teams in the Spring Experiment. These will be combined with separate deterministic WRF forecasts at 3 km grid spacing, contributed by NCAR and EMC. Additional data fields from the CAPS runs will be posted on the web in realtime for external verification purposes. These include side by side comparisons of 2-km forecast composite reflectivity with the NSSL national reflectivity mosaic at 5-minute intervals and graphical displays of a large array of 2-D fields and ensemble products, including postage stamps and probability maps

Over 1000 CPUs at the Pittsburgh Supercomputing Center (PSC) will be used to produce the forecasts while additional processors at the University of Oklahoma Supercomputing Center for Education and Research (OSCER) will be used for post-processing. A special super-high-speed link capable of 200 MB/s will be set up between PSC and OSCER for data transfer.

Results of realtime forecasts and preliminary retrospective analysis on selected cases will be presented at the conference.

Available online at ://http://ams.confex.com/ams/pdfpapers/124587.pdf.

Yeary, M., R. Palmer, M. Xue, T. Y. Yu, G. Zhang, A. Zahrai, J. Crain, Y. Zhang, R. Doviak, Q. Xu, P. Chilson, 2008: Introduction to multi-channel receiver development for the realization of multi-mission capabilities at the National Weather Radar Testbed. Extended Abstracts, 24rd Conference on Interactive Information Processing Systems (IIPS), New Orleans, LA, USA, AMS, 9A.3.

Yussouf, N., D. J. Stensrud, 2006: Prediction of near surface variables at independent locations from a bias-corrected ensemble forecasting system. Monthly Weather Review, 134, 3415-3424.

The ability of a multimodel short-range bias-corrected ensemble (BCE) forecasting system, created as part of NOAA’s New England High Resolution Temperature Program during the summer of 2004, to obtain accurate predictions of near-surface variables at independent locations within the model domain is explored. The original BCE approach produces bias-corrected forecasts only at National Weather Service (NWS) observing surface station locations. To extend this approach to obtain bias-corrected forecasts at any given location, an extended BCE technique is developed and applied to the independent observations provided by the Oklahoma Mesonet. First, a Cressman weighting scheme is used to interpolate the bias values of 2-m temperature, 2-m dewpoint temperature, and 10-m wind speeds calculated from the original BCE approach at the NWS observation station locations to the Oklahoma Mesonet locations. These bias values are then added to the raw numerical model forecasts bilinearly interpolated to this same specified location. This process is done for each forecast member within the ensemble and at each forecast time. It is found that the performance of the extended BCE is very competitive with the original BCE approach across the state of Oklahoma. Therefore, a simple postprocessing scheme like the extended BCE system can be used as part of an operational forecasting system to provide reasonably accurate predictions of near surface variables at any location within the model domain.

Yussouf, N., D. J. Stensrud, 2007: Bias-Corrected Short-Range Ensemble Forecasts of Near-Surface Variables during the 2005/06 Cool Season. Weather and Forecasting, 22, 1274-1286.

A postprocessing method initially developed to improve near-surface forecasts from a summertime multimodel short-range ensemble forecasting system is evaluated during the cool season of 2005/06. The method, known as the bias-corrected ensemble (BCE) approach, uses the past complete 12 days of model forecasts and surface observations to remove the mean bias of near-surface variables from each ensemble member for each station location and forecast time. In addition, two other performance-based weighted-average BCE schemes, the exponential smoothing method BCE and the minimum variance estimate BCE, are implemented and evaluated. Values of root-mean-squared error from the 2-m temperature and dewpoint temperature forecasts indicate that the BCE approach outperforms the routinely available Global Forecast System (GFS) model output statistics (MOS) forecasts during the cool season by 9% and 8%, respectively. In contrast, the GFS MOS provides more accurate forecasts of 10-m wind speed than any of the BCE methods. The performance-weighted BCE schemes yield no significant improvement in forecast accuracy for 2-m temperature and 2-m dewpoint temperature when compared with the original BCE, although the weighted BCE schemes are found to improve the forecast accuracy of the 10-m wind speed. The probabilistic forecast guidance provided by the BCE system is found to be more reliable than the raw ensemble forecasts. These results parallel those obtained during the summers of 2002–04 and indicate that the BCE method is a promising and inexpensive statistical postprocessing scheme that could be used in all seasons.

Yussouf, N., D. J. Stensrud, 2008: Reliable Probabilistic Quantitative Precipitation Forecasts from a Short-Range Ensemble Forecasting System during the 2005/06 Cool Season. Monthly Weather Review, 136, 2157-2172.

A simple binning technique developed to produce reliable probabilistic quantitative precipitation forecasts (PQPFs) from a multimodel short-range ensemble forecasting system is evaluated during the cool season of 2005/06. The technique uses forecasts and observations of 3-h accumulated precipitation amounts from the past 12 days to adjust the present day’s 3-h quantitative precipitation forecasts from each ensemble member for each 3-h forecast period. Results indicate that the PQPFs obtained from this simple binning technique are significantly more reliable than the raw (original) ensemble forecast probabilities. Brier skill scores and areas under the relative operating characteristic curve also reveal that this technique yields skillful probabilistic forecasts of rainfall amounts during the cool season. This holds true for accumulation periods of up to 48 h. The results obtained from this wintertime experiment parallel those obtained during the summer of 2004. In an attempt to reduce the effects of a small sample size on two-dimensional probability maps, the simple binning technique is modified by implementing 5- and 9-point smoothing schemes on the adjusted precipitation forecasts. Results indicate that the smoothed ensemble probabilities remain an improvement over the raw (original) ensemble forecast probabilities, although the smoothed probabilities are not as reliable as the unsmoothed adjusted probabilities. The skill of the PQPFs also is increased as the ensemble is expanded from 16 to 22 members during the period of study. These results reveal that simple postprocessing techniques have the potential to provide greatly improved probabilistic guidance of rainfall events for all seasons of the year.

Yussouf, N., D. J. Stensrud, 2008: Impact of high temporal frequency radar data assimilation on storm-scale NWP model simulations. Preprints, 24th Conference on Severe Local Storms, Savannah, GA, USA, Amer. Meteor. Soc., 9B.1. [Available from Nusrat Yussouf, 120 David L. Boren Blvd., Norman, OK, USA, 73072.]

Radial-velocity and reflectivity observations from Doppler radars can provide important information for initializing numerical storm-scale prediction models and in diagnosing the evolution of severe weather events like thunderstorms and tornadoes. Recent research indicates that the assimilation of Doppler radar data using the Ensemble Kalman Filter (EnKF) approach generates good estimates of storm structure. While the conventional Doppler radar takes 4-5 minutes to scan a thunderstorm, the new and emerging Phased Array Radar (PAR) rapid and adaptive scanning technology can scan the same storm in less than a minute and can enhance the scanning angles in real time to get a better depiction of the storm top. Thus, in an effort to explore the impact of high temporal frequency PAR observations in storm assimilation, Observing System Simulation Experiments (OSSEs) are designed using the EnKF as a method for initializing storm-scale numerical forecast models.

Several different OSSEs are conducted with radial-velocity and reflectivity observations constructed from simulated supercells in native radar coordinates using a realistic volume averaging technique. Two sets of experiment are run for each OSSE. One experiment assimilates the simulated Doppler radar observations while the other experiment assimilates the high temporal frequency PAR observations. Results obtained are compared to document the value of new PAR observations to the creation of improved storm analyses and short-range ensemble forecasts.

Available online at ://http://ams.confex.com/ams/pdfpapers/141555.pdf.

Zhang, P., S. Liu, Q. Xu, Lulin Song, 2005: Storm targeted radar wind retrieval system. 32nd Conference on Radar Meteorology, Albuquerque, NM, USA, American Meteorological Society, CD-ROM, P8R1.

Zhang, P., S. Liu, Q. Xu, 2005: Quality control of Doppler velocities contaminated by migrating birds. Part I: Feature extraction and quality control parameters. Journal of Atmospheric and Oceanic Technology, 22, 1105-1113.

Zhang, S. W., C. J. Qiu, Q. Xu, 2005: Reply. Journal of Applied Meteorology, 44, 551-552.

Zhang, G., Q. Cao, M. Xue, P. Chilson, M. Morris, R. Palmer, J. Brotzke, T. Schuur, E. Brandes, K. Ikeda, A. Ryzhkov, D. Zrnic, E. Jessup, 2008: A field experiment to study rain microphysics using video disdrometers and polarimetric S and X-band radars. Preprints, Symposium on Recent Developments in Atmospheric Applications of Radar and Lidar, New Orleans, LA, USA, American Meteorological Society, P2.23.

Zhang, J., K. Howard, X. Xu, 2008: A warm season radar QPE algorithm using adaptive Z-R relationships. Proc. World Environmental and Water Resources Congress 2008, Honolulu, HI, USA, Amer. Soc. Civil Engineers, CD-ROM, 420.pdf.

Zhao, Q., J. Cook, Q. Xu, P. Harasti, 2005: Improving very-short-term storm predictions by assimilating radar data into a mesoscale NWP model. 32nd Conference on Radar Meteorology, Albuquerque, NM, USA, American Meteorological Society, CD-ROM, XXXX.

Zhao, Q., J. Cook, Q. Xu, P. Harasti, 2006: Using radar wind observations to improve mesoscale numerical weather prediction. Weather and Forecasting, 21, 502-522.

Zhao, Q., J. Cook, Q. Xu, P. Harasti, 2008: Improving short-term storm predictions by assimilating both radar radial-wind and reflectivity observations.. Weather and Forecasting, 23, 373-391.

Ziegler, C. L., M. S. Buban, E. N. Rasmussen, 2007: A Lagrangian Objective Analysis Technique for Assimilating In Situ Observations with Multiple-Radar-Derived Airflow. Monthly Weather Review, 135, 2417-2442.

A new Lagrangian analysis technique is developed to assimilate in situ boundary layer measurements using multi-Doppler-derived wind fields, providing output fields of water vapor mixing ratio, potential temperature, and virtual potential temperature from which the lifting condensation level (LCL) and relative humidity (RH) fields are derived. The Lagrangian analysis employs a continuity principle to bidirectionally distribute observed values of conservative variables with the 3D, evolving boundary layer airflow, followed by temporal and spatial interpolation to an analysis grid. Cloud is inferred at any grid point whose height z > zLCL or equivalently where RH ≥ 100%. Lagrangian analysis of the cumulus field is placed in the context of gridded analyses of visible satellite imagery and photogrammetric cloud-base area analyses. Brief illustrative examples of boundary layer morphology derived with the Lagrangian analysis are presented based on data collected during the International H2O Project (IHOP): 1) a dryline on 22 May 2002; 2) a cold-frontal–dryline “triple point” intersection on 24 May 2002. The Lagrangian analysis preserves the sharp thermal gradients across the cold front and drylines and reveals the presence of undulations and plumes of water vapor mixing ratio and virtual potential temperature associated with deep penetrative updraft cells and convective roll circulations. Derived cloud fields are consistent with satellite-inferred cloud cover and cloud-base locations.

Ziegler, C. L., E. N. Rasmussen, M. S. Buban, Y. P. Richardson, L. J. Miller, R. M. Rabin, 2007: The "Triple Point" on 24 May 2002 during IHOP. Part II: Ground-Radar and In Situ Boundary Layer Analysis of Cumulus Development and Convection Initiation. Monthly Weather Review, 135, 2443-2472.

Cumulus formation and convection initiation are examined near a cold front–dryline “triple point” intersection on 24 May 2002 during the International H2O Project (IHOP). A new Lagrangian objective analysis technique assimilates in situ measurements using time-dependent Doppler-derived 3D wind fields, providing output 3D fields of water vapor mixing ratio, virtual potential temperature, and lifted condensation level (LCL) and water-saturated (i.e., cloud) volumes on a subdomain of the radar analysis grid. The radar and Lagrangian analyses reveal the presence of along-wind (i.e., longitudinal) and cross-wind (i.e., transverse) roll circulations in the boundary layer (BL). A remarkable finding of the evolving radar analyses is the apparent persistence of both transverse rolls and individual updraft, vertical vorticity, and reflectivity cores for periods of up to 30 min or more while moving approximately with the local BL wind. Satellite cloud images and single-camera ground photogrammetry imply that clouds tend to develop either over or on the downwind edge of BL updrafts, with a tendency for clouds to elongate and dissipate in the downwind direction relative to cloud layer winds due to weakening updrafts and mixing with drier overlying air. The Lagrangian and radar wind analyses support a parcel continuity principle for cumulus formation, which requires that rising moist air parcels achieve their LCL before moving laterally out of the updraft. Cumuli form within penetrative updrafts in the elevated residual layer (ERL) overlying the moist BL east of the triple point, but remain capped by a convection inhibition (CIN)-bearing layer above the ERL. Dropsonde data suggest the existence of a convergence line about 80 km east of the triple point where deep lifting of BL moisture and locally reduced CIN together support convection initiation.

Ziegler, C. L., E. N. Rasmussen, M. Buban, Y. Richardson, L. J. Miller, R. Rabin, 2005: The boundary layer cumulus formation process near a cold frontal-dryline intersection on 24 May 2002 during IHOP. Preprints, 11th Conference on Mesoscale Processes, Albuquerque, NM, USA, AMS, J6J.2.

Ziegler, C. L., E. Mansell, J. Straka, D. MacGorman, D. Burgess, 2007: Impact of varying inversion strength on the electrification, lightning, kinematics, and microphysics in a simulated supercell storm. Preprints, 13th International Conference on Atmospheric Electricity, Beijing, China, International Commission on Atmospheric Electricity, 225-228.

Ziegler, C. L., E. R. Mansell, J. M. Straka, D. R. MacGorman, D. W. Burgess, 2008: Impact of Spatially Varying Inversion Strength on the Evolution of a Simulated Supercell Storm.. Extended Abstracts, 24th Conference on Severe Local Storms, Savannah, GA, USA, American Meteorological Society, P10.10.

Ziegler, C. L., K. Kuhlman, M. Biggerstaff, D. Betten, L. Wicker, E. Mansell, D. MacGorman, 2008: Evolution of low-level rotation in the tornadic 29 May 2004 Geary, Oklahoma supercell storm. Extended Abstracts, 24th Conference on Severe Local Storms, Savannah, GA, USA, AMS, 2.2.

Two mobile C-band Doppler SMART radars sampled a high-precipitation, tornadic supercell storm on 29 May 2004 during its severe, right-moving phase. Bulk parameters of the storm’s near-environment were obtained from approximately hourly, storm-following mobile GPS advanced upper-air sounding system (MGAUS) profiles obtained within the storm’s inflow extending from its initiation stage through the time of maximum low-level rotation in central Oklahoma. Analysis of the high-resolution, dual-Doppler three-dimensional airflow focuses on identifying downdraft source regions and estimating vorticity dynamical processes that contribute to the development of the low-level mesocyclonic and tornado-cyclonic circulations.

During the storm’s most intense phase, a storm-scale rear-flank downdraft boundary (RFDB) intersected the conventional forward flank downdraft boundary (FFDB) within the wrapping inflow to the intensifying low-level mesocyclone. The combined dataset facilitates preliminary testing of the hypothesis that the low-level mesocyclone is intensified via the classical mechanism of solenoidal (horizontal streamwise) vorticity generation followed by tilting and stretching with contributions from both the RFDB and FFDB. The evolution of the low-level angular momentum field will also be examined as a preliminary test of the alternate hypothesis that RFD development combined with strong stratification of horizontal angular momentum may combine to trigger a corner-flow collapse process leading to low-level mesocyclogenesis. This case illustrates the likely hypothesis testing procedures for other supercell storms sampled by the SMART radars during the upcoming VORTEX2 field project.