Table of ContentsTable of Contents 
Previous Chapter There are two categories of weather elements: General and Service-specific. General weather elements (GWE) are those applying to multiple services. This set contains elements that:
There are a few product parameters are not derived from weather elements and hence must be manually created using other means than AFPS. Chapter 10, Weather Element and Product Parameter Relationships, on page97 describes the relationships between the weather elements and product parameters. Specifically, Figure29 on page110 and Figure30 on page111 show product parameters that must be manually input.
Group Name - Several weather elements have been grouped together to facilitate easier manipulation by the forecaster. The forecaster can select a grouping and then individually manipulate any component of that grouping. For those weather elements represented by bounded areas, the area covered by each component of a grouping is always identical to the area covered by the grouping. For those weather elements represented by continuous fields, the groupings simply serve as a technique to display related parameters together.
Name - The name of the weather element.
Value Representation - The representation of the value of the parameter. A parameter's value may be represented in one of three ways:
Range Representation - The approximate range of the weather element. For those elements which are not represented by continuous numbers, details are given in additional tables.
Units Representation - The units of the weather elements as stored in the database and displayed to the user. The resolution of the weather element can generally be determined from the units representation. For those elements which are not represented by continuous numbers, details are given in additional tables.
Temporal Resolution - The smallest temporal unit over which the parameter may be defined. Most parameters have a nominal resolution of 1 hour. However, many parameters require less temporal resolution after the first 24 hours of the forecast. It's likely that the temporal resolution for each parameter may not be a single number, but variable, where the actual resolution decreases with increasing forecast projection. In this case, the temporal resolution value in the following table indicates the highest resolution for which the parameter may be defined.
Several data attributes are the same for most weather elements. These are not included in the tables, but are listed below.
Spatial Domain - The physical domain over which the parameter exists. Only three domains are possible: the forecast area (WFO) where parameters will be defined over the entire WFO area, TAF (terminal forecast) points where parameters will be defined at a point versus time, and TWEB routes where parameters will be defined at user-definable route segments versus time.
Temporal Domain - The time over which the parameter must be defined. Most parameters require 0 to 6 days, but TAF and TWEB parameters are limited to 0 to 24 hours and 0 to 18 hours, respectively.
Spatial Resolution - The smallest spatial unit over which the parameter may be defined. This attribute applies to spatially continuous data only. The typical resolution is 10 kilometers. Bounded area data are defined with global coordinates, so the concept of spatial resolution is not applicable.
Temporal Representation - The structure we have chosen for the database requires that all parameters be represented as stepped in time. That is, the value of the parameter is constant over a period of time, then abruptly changes. In practice, the 1-hour step size is small enough to appear smooth on the time scale covered by most forecasts.
Table 39 - GWE Summary
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Value Spatial Units Range
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Wind Speed Numerical Continuous knot 0-200 1 hour
Wind
Wind Direction Numerical Continuous degrees 0-359 1 hour
Wind Gust Numerical Continuous knots 0-200 1 hour
Temperature Numerical Continuous degrees F. -100 - +130 1 hour
Dew Point Numerical Continuous degrees F. -100 - +130 1 hour
Probability of Precipitation Step- Continuous percent 0, 5, then 10 - 6 hours
Numerical 100 by 10s
Cloud Type Categorical Bounded Area Table45, page90 1 hour
Cloud
Cloud Base Numerical Bounded Area 100s ft MSL 0 - 800 1 hour
Cloud Top Numerical Bounded Area 100s ft MSL 0 - 800 1 hour
Cloud Probability Categorical Bounded Area Table46, page90 1 hour
Cloud Amount Step- Bounded Area Table47, page91 1 hour
Numerical
Weather Type Categorical Bounded Area Table48, page91 1 hour
Weather
Weather Intensity Categorical Bounded Area Table49, page91 1 hour
Weather Coverage/Proba Categorical Bounded Area Table50, page92 1 hour
bility
Visibility Step- Bounded Area Table51, page92 1 hour
Numerical
Q.P.F. Probability "A" Numerical Continuous 0.01 inches 0 - 2500 3 hours
QPF
Q.P.F. Probability "B" Numerical Continuous 0.01 inches 0 - 2500 3 hours
Q.P.F. Probability "C" Numerical Continuous 0.01 inches 0 - 2500 3 hours
Snow Accumulation Numerical Continuous inches 0 - 200 3 hours
Freezing Level Numerical Continuous 100s ft MSL 0 - 200 6 hours
Inversion Type Categorical Bounded Area Table52, page92 6 hours
Inversion
Inversion Top Numerical Bounded Area 100s ft AGL 0 - 100 6 hours
Inversion Base Numerical Bounded Area 100s ft AGL 0 - 100 6 hours
Maximum Temperature Numerical Continuous degrees F. -100 - +130 12 hours
Minimum Temperature Numerical Continuous degrees F. -100 - +130 12 hours
Maximum Relative Humid Step- Continuous percent 0 - 100 in 12 hours
ity Numerical 10% steps
Minimum Relative Humid Step- Continuous percent 0 - 100 in 12 hours
ity Numerical 10% steps
Sky Condition Categorical Bounded Area N/A CLR, SCT, 1 hour
BKN, BKN,
OVC, OVC
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Table 40 - SWE TAF Summary ---------------------------------------------------------------------------------------------- Value Units Range ---------------------------------------------------------------------------------------------- Prevailing Prevailing Wind Speed Numerical knots 0 - 200 1 hour Wind Prevailing Wind Direction Numerical degrees 0 - 359 1 hour Prevailing Wind Gust Numerical knots 0 - 200 1 hour Chance Chance Wind Speed Numerical knots 0 - 200 1 hour Wind Chance Wind Direction Numerical degrees 0 - 359 1 hour Chance Wind Gust Numerical knots 0 - 200 1 hour Occasional Occasional Wind Speed Numerical knots 0 - 200 1 hour Wind Occasional Wind Direction Numerical degrees 0 - 359 1 hour Occasional Wind Gust Numerical knots 0 - 200 1 hour Prevailing Prevailing Cloud Type Categorical Table45, page90 1 hour Cloud Prevailing Cloud Base Numerical 100s ft AGL 0 - 800 1 hour Prevailing Cloud Top Numerical 100s ft AGL 0 - 800 1 hour Prevailing Cloud Amount Categorical Table47, page91 1 hour Chance Chance Cloud Type Categorical Table45, page90 1 hour Cloud Chance Cloud Base Numerical 100s ft AGL 0 - 800 1 hour Chance Cloud Top Numerical 100s ft AGL 0 - 800 1 hour Chance Cloud Amount Categorical Table47, page91 1 hour Occasional Occasional Cloud Type Categorical Table45, page90 1 hour Cloud Occasional Cloud Base Numerical 100s ft AGL 0 - 800 1 hour Occasional Cloud Top Numerical 100s ft AGL 0 - 800 1 hour Occasional Cloud Amount Categorical Table47, page91 1 hour Prevailing Prevailing Weather Type Categorical Table53, page93 1 hour Weather Prevailing Weather Intensity Categorical Table53, page93 1 hour Chance Chance Weather Type Categorical Table53, page93 1 hour Weather Chance Weather Intensity Categorical Table53, page93 1 hour Occasional Occasional Weather Type Categorical Table53, page93 1 hour Weather Occasional Weather Intensity Categorical Table53, page93 1 hour Prevailing Visibility Step-Numerical Table51, page92 1 hour Chance Visibility Step-Numerical Table51, page92 1 hour Occasional Visibility Step-Numerical Table51, page92 1 hour ----------------------------------------------------------------------------------------------
Table 41 - SWE TWEB Summary -------------------------------------------------------------------------------------------------------- Value Units Range -------------------------------------------------------------------------------------------------------- Isolated Isolated Cloud Base Numerical 100s ft MSL 0 - 800 1 hour Cloud Isolated Cloud Top Numerical 100s ft MSL 0 - 800 1 hour Isolated Cloud Amount Categorical N/A CLR, SCT, -BKN, 1 hour BKN, -OVC, OVC Local Local Cloud Base Numerical 100s ft MSL 0 - 800 1 hour Cloud Local Cloud Top Numerical 100s ft MSL 0 - 800 1 hour Local Cloud Amount Categorical N/A CLR, SCT, -BKN, 1 hour BKN, -OVC, OVC Areas Areas Cloud Base Numerical 100s ft MSL 0 - 800 1 hour Cloud Areas Cloud Top Numerical 100s ft MSL 0 - 800 1 hour Areas Cloud Amount Categorical N/A CLR, SCT, -BKN, 1 hour BKN, -OVC, OVC Widespread Widespread Cloud Base Numerical 100s ft MSL 0 - 800 1 hour Cloud Widespread Cloud Top Numerical 100s ft MSL 0 - 800 1 hour Widespread Cloud Amount Categorical N/A CLR, SCT, -BKN, 1 hour BKN, -OVC, OVC Isolated Isolated Weather Type Categorical Table48, page91 1 hour Weather Isolated Weather Intensity Categorical Table49, page91 1 hour Local Local Weather Type Categorical Table48, page91 1 hour Weather Local Weather Intensity Categorical Table49, page91 1 hour Areas Areas Weather Type Categorical Table48, page91 1 hour Weather Areas Weather Intensity Categorical Table49, page91 1 hour Widespread Widespread Weather Type Categorical Table48, page91 1 hour Weather Widespread Weather Intensity Categorical Table49, page91 1 hour Isolated Surface Visibility Step-Numerical Table51, page92 1 hour Local Surface Visibility Step-Numerical Table51, page92 1 hour Areas Surface Visibility Step-Numerical Table51, page92 1 hour Widespread Surface Visibility Step-Numerical Table51, page92 1 hour Isolated Hazards Categorical Table54, page93 1 hour Local Hazards Categorical Table54, page93 1 hour Areas Hazards Categorical Table54, page93 1 hour Widespread Hazards Categorical Table54, page93 1 hour --------------------------------------------------------------------------------------------------------
Table 42 - SWE Fire Weather Summary ----------------------------------------------------------------------------------------------------------- Value Spatial Units Range ----------------------------------------------------------------------------------------------------------- Transport Transport Wind Direc Numerical Continuous degrees 0 - 359 12 hours Wind tion Transport Wind Speed Numerical Continuous knots 0 - 200 12 hours Free Air Free Air Wind Direction Numerical Continuous degrees 0 - 359 12 hours Wind Free Air Wind Speed Numerical Continuous knots 0 - 200 12 hours 10-hour Fuel Moisture Numerical Continuous percent 0 - 100 24 hours Precipitation Duration Step-Numerical Continuous hours 0 - 24 12 hours Mixing Depth Numerical Continuous 100s ft MSL 0 - 200 6 hours Stability Categorical Bounded Area Table55, page94 6 hours Lightning Activity Level Categorical Bounded Area Table56, page94 6 hours Haines Index Step-Numerical Continuous 0 - 10 12 hours Chance of Wetting Rain Step-Numerical Continuous percent 0 - 100 in 12 hours 10% steps -----------------------------------------------------------------------------------------------------------
Table 43 - SWE Agriculture Summary ---------------------------------------------------------------------------------------------------- Value Spatial Units Range ---------------------------------------------------------------------------------------------------- Dew Intensity Categorical Bounded Area Table57, page94 12 hours Dew Dew Dryoff Time Step-Numerical Continuous local hour 0 - 23 12 hours Drying Conditions Categorical Bounded Area N/A Poor, Fair, 12 hours Good, Excellent Hours of Sunshine Numerical Continuous hours 0 - 24 24 hours Minimum Dew Point Numerical Continuous degrees F. -50 - +130 12 hours ----------------------------------------------------------------------------------------------------
Table 44 - SWE Marine Summary ----------------------------------------------------------------------------------------------- Value Spatial Units Range ----------------------------------------------------------------------------------------------- Wave Height Numerical Continuous feet 0 - 60 6 hours Superstructure Icing Categorical Bounded Area Table58, page94 6 hours Swell Height Numerical Continuous feet 0 - 60 6 hours Swell Swell Direction Numerical Continuous degrees 0 - 359 6 hours -----------------------------------------------------------------------------------------------
Table 45 - Cloud Types ---------------------------------------------------- Symbol Description ---------------------------------------------------- <no symbol> Any cloud other than cumulonimbus CB Cumulonimbus ----------------------------------------------------
Table 46 - Cloud Probabilities -------------------------------- Symbol Description -------------------------------- SLGT CHC Slight Chance CHC Chance OCNL Occasional <no symbol> Definite --------------------------------
Table 47 - Cloud Amount Values --------------------------------------------------- Amount Descriptive Word Amount Descriptive Word and and Symbol Symbol --------------------------------------------------- 0 Clear (CLR) 4/10 Broken (BKN) 1/10 5/10 Scattered (SCT) 2/10 6/10 3/10 7/10 8/10 9/10 10/10 Overcast (OVC) ---------------------------------------------------
Table 48 - Weather Types ------------------------------------------------------------------------ Symbol Description Symbol Description Symbol Description ------------------------------------------------------------------------ T+ Severe Thunderstorm S Snow BN Blowing Sand T Thunderstorm SW Snow Showers BD Blowing Dust R Rain SP Snow Pellets IF Ice Fog RW Rain Showers SG Snow Grains H Haze L Drizzle IC Ice Crystals K Smoke ZR Freezing Rain A Hail D Dust ZL Freezing Drizzle F Fog BY Blowing Spray IP Ice Pellets GF Ground Fog BR Mist IPW Ice Pellet Showers BS Blowing Snow VA Volcanic Ash ------------------------------------------------------------------------
Table 49 - Weather Intensities ------------------------------ Symbol Description ------------------------------ ++ Very Heavy + Heavy <no symbol> Moderate - Light -- Very Light ------------------------------
Table 50 - Weather Coverage Values ------------------------------------------------- Symbol Values Symbol Values ------------------------------------------------- ISO Isolated OCNL Occasional WSCT Widely Scattered SGLT CHC Slight Chance SCT Scattered CHC Chance WIDE Widespread LKLY Likely -------------------------------------------------
Table 51 - Visibility Values ---------------------------------------------------------------------------- Values ---------------------------------------------------------------------------- 0, 1/4, 1/2, 3/4, 1, 11/2, 2, 21/2, 3, 4, 5, 6, greater than 6 statute miles ----------------------------------------------------------------------------
Table 52 - Inversion Type Values ----------------- Symbol Values ----------------- R Radiative A Advective ? Unknown -----------------
Table 53 - TAF Significant Weather Codes ----------------------------------------------------------------------------------------------------------------------------------- TAF Description TAF Description Code Code ----------------------------------------------------------------------------------------------------------------------------------- Qualifier Intensity - Light Weather Phenomena Precipitation DZ Drizzle <none> Moderate RA Rain + Heavy SN Snow VC In the vicinity SG Snow Grains Descriptor MI Shallow IC Diamond Dust (Ice Crystals) BC Patches PE Ice Pellets DR Drifting GR Hail BL Blowing GS Small hail and/or snow pellets SH Showers Obscuration BR Mist TS Thunderstorm FG Fog FZ Supercooled FU Smoke VA Volcanic ash DU Widespread dust SA Sand ??(a) Spray HZ Haze Other PO Well developed dust/sand whirls SQ Squalls FC Funnel cloud (tornado or waterspout) SS Sandstorm DS Duststorm -----------------------------------------------------------------------------------------------------------------------------------
Table 54 - Hazard Values ------------------------------------------------------------------------------------ Phrase Description ------------------------------------------------------------------------------------ MTNS OBSCD ABV hhh Mountains are obscured by low clouds above the specified height above sea level.. ALL PASSES OBSCD All mountain passes are obscured in clouds and/or precipitation. ------------------------------------------------------------------------------------
Table 55 - Stability Values -------------------------- Value Description -------------------------- A Extremely Unstable B Moderately Unstable C Slightly Unstable D Neutral E Slightly Stable --------------------------
Table 56 - Lightning Activity Level Values ---------------------------------------------------------------------------------------------------- Value Description ---------------------------------------------------------------------------------------------------- 1 No thunderstorms. 2 Few building cumulus only occasionally reaching cumulus congestus stage; single CB in forecast area. 3 Scattered cumulus and cumulus congestus; widely scattered CBs. Cloud-to-ground light ning averaging 1-2 per minute maximum. 4 Growing cumulus and cumulus congestus over 1/10 to 3/10 of the area. Scattered cloud-to- ground lightning in area averaging 2-3 strikes per minute. 5 Cumulus congestus common over area, occasionally obscuring the sky. Moderate to heavy rain associated with CBs; light to moderate rain preceding and following lightning activity. Lightning flashes occurring steadily at some place in or during storm period. Maximum cloud-to-ground flash rate greater than 3 per minute. 6 Scattered towering cumulus with few at thunderstorm stage. Very limited horizontal extent with high bases (15000-17000 feet MSL), virga in most prominent hydrometeor form. Lightning flash rate is low, averaging less than 1 to 3 per 5 minute period each storm. ----------------------------------------------------------------------------------------------------
Table 57 - Dew Intensity Categories ----------------------------------------------------- Symbol Categories Symbol Categories ----------------------------------------------------- VL Very light dew MH Moderate to heavy dew L Light dew H Heavy dew M Moderate dew VH Very heavy dew -----------------------------------------------------
Table 58 - Superstructure Icing Values ------------------------------------------------------------- Symbol Value Description ------------------------------------------------------------- L Light Up to 0.3 inches per hour accretion M Moderate 0.3 to 0.8 inches per hour accretion H Heavy 0.8 to 2.0 inches per hour accretion VH Very Heavy 2.0 inches and greater per hour accretion -------------------------------------------------------------
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