/wsom/manual/IMAGES/d221.gif
U.S. DEPARTMENT OF COMMERCEMay 22, 1991 W/OM13
TO: All Holders of Operations Manual
SUBJECT: Transmittal Memorandum for Operations Manual Issuance 91-7
1. Material Transmitted: WSOM Chapter D-22, In-flight Aviation Weather Advisories.
2. Summary:
The entire chapter is being reissued. The following are major changes:
a. AIRMETs will be scheduled products issued every 6 hours with amendments issued as necessary. They will have fixed alphanumeric designators of Zulu for icing and freezing level, Tango for turbulence, strong surface winds, and low level wind shear, and Sierra for Instrument Flight Rules (IFR) and mountain obscuration.
b. IFR meteorological conditions shall now be described solely in the AIRMET bulletins and will no longer be redundantly described in the Area Forecast (FA).
c. The alphanumeric designators for nonconvective SIGMETs have been changed and will now include only N through Y excluding the AIRMET designators, S and T.
d. Nonconvective SIGMETs shall be issued for volcanic eruptions and when, in the forecasters' judgment, a hazard to aircraft operations due to volcanic ash is known to exist. The eruption issuance is mandatory regardless of the visibility within any ash and/or steam cloud and regardless of the areal coverage of the cloud. In addition, SIGMETs for volcanic ash should be updated when any information becomes available which will increase the effectiveness of the advisory.
e. Nonconvective SIGMETs may now expire without cancellation when conditions end within 30 minutes of the forecast ending time of the phenomenon or of the SIGMETs expiration time and those conditions are not expected to continue
f. The location of conditions requiring the issuance of SIGMETs and AIRMETs shall continue to be coordinated as if no FA region boundaries exist and then may be recoordinated within the affected FA region boundaries using a minimum number of LOCs. When this method of issuance is used, instructions allow the in-flight advisory areas to overlap FA region boundaries where necessary to simplify area outlines.
g. When a special Convective SIGMET is issued after the scheduled Convective SIGMETs have been issued on the hour, the special shall be added to the previous hour's bulletin and transmitted.
h. Instructions for backup operations during an outage at the National Severe Storms Forecast Center have been incorporated. These affect both the FA and the In-flight Advisory Programs.
3. Effect on Other Instructions:
This chapter supersedes:
WSOM Chapter D-22, Issuance 82-19, dated November 2, 1982; Issuance 83-4, dated March 30, 1983; OML 2-83, dated January 20, 1983; OML 4-86, dated April 7, 1986; and ROML A-02-85 dated March 1, 1985.
This chapter will be effective 0735Z May 30, 1991.
Elbert W. Friday, Jr.
Assistant Administrator
for Weather Services
Issue Date Org. Code NATIONAL WEATHER SERVICE Part Chap.
5-22-91 W/OM13 Operations Manual D 22
IN-FLIGHT AVIATION WEATHER ADVISORIES
Table of Contents:
1. Purpose
2.1 SIGMET
2.1.1 Convective SIGMET in Conterminous United States
2.1.2 Nonconvective SIGMET in Conterminous United States
2.1.3 SIGMETs in Alaska, Hawaii and Puerto Rico
5. Convective SIGMETs
5.1 Convective SIGMET Bulletins
5.2 Convective SIGMET Header
5.3 Convective SIGMET Contents
5.3.1 Isolated Severe/Embedded Thunderstorm
5.3.2 Line of Thunderstorms
5.3.3 Area of Thunderstorms
5.3.4 Examples
5.3.5 Special Convective SIGMETs
5.3.6 Bulletins for Activity Not Meeting WST Criteria
7. Nonconvective SIGMETs in Conterminous United States
7.1 SIGMET Header
7.1.1 Header Formats
7.1.2 Multiple Area Designators
7.2 Nonconvective SIGMET Message Texts
7.2.1 Severe and Extreme Turbulence
7.2.2 Clear Air Turbulence (CAT)
7.2.3 Severe Icing
7.2.4 Widespread Dust Storms, Sandstorms, and Volcanic Ash
7.2.5 Volcanic Eruption
7.2.6 Relationship of Nonconvective SIGMETs to
Tropical Storm and/or Hurricane Advisories
7.2.7 SIGMET Cancellations
7.3 Examples
8. AIRMETs
8.1 AIRMET Header
8.1.1 Header Format
8.1.2 Multiple Area Designation
8.2 AIRMET Message Texts
8.2.1 AIRMET Cancellations
8.2.2 Moderate Turbulence
8.2.3 Strong Surface Winds
8.2.4 Nonconvective LLWS Potential
8.2.5 Moderate Icing
8.2.6 IFR Ceilings and/or Visibility
8.2.7 Extensive Mountain Obscuration
8.2.8 Relationship of AIRMETs to Tropical Storm and/or Hurricane Advisories
8.2.9 Examples
11. Procedures for Backup of the NAWAU
11.1 Policy
11.2 Procedures
11.2.1 Test Requirements
11.2.2 Notifications
11.2.3 Operations
11.2.4 Communications
12. Retention
Exhibits:
D-22-1 In-flight Advisory Plotting Chart
D-22-2 Turbulence Reporting Criteria Table
D-22-3 Forecasting Guide on Turbulence Intensity Table
D-22-4 Airframe Icing Reporting Table
1. Purpose. This chapter addresses the National Weather Service (NWS) policies and procedures regarding in-flight aviation weather advisories for domestic airspace (i.e., contiguous United States, Alaska, and Hawaii). The In-flight Aviation Weather Advisory program provides information for pilots of en route aircraft concerning weather phenomena of sufficient extent and/or intensity as to be potentially hazardous to aircraft operations. It is intended to serve the needs of both civilian and military aviation as a "common system" aviation weather safety program. The instructions of this chapter do not apply to the issuance of International In-flight Aviation Weather Advisories (see WSOM Chapter D-38). Center Weather Advisories (CWA) are short-range regional In-flight Advisories provided by Center Weather Service Units (CWSU). These CWAs are issued in accordance with policies and procedures detailed in WSOM Chapter D-25.
2. Types of Advisories. The Federal Aviation Regulations make various distinctions between aviation operating equipment and personnel. Some weather phenomena or intensities have an impact on all aviation operations. The NWS recognizes that some weather phenomena or intensities have greater impact or present a greater hazard to some classes or types of aircraft than others. The NWS also recognizes that certain types of operators, and operations by pilots without certain ratings or certifications, are significantly more impacted by the occurrence or forecast occurrence of certain weather phenomena.
The In-flight Aviation Weather Advisory program has addressed these diverse requirements for information by the issuance of two types of products, Significant Meteorological (SIGMET) Advisories, and Airman's Meteorological (AIRMET) Advisories. However, in the past few years the mixing of aircraft vulnerabilities to certain phenomena, changes in operating altitudes (small planes higher and larger planes lower), interest in conditions affecting passenger comfort as well as safety, and expanding pilot and dispatcher requirements for information have made this approach less effective.
The distinctions between the weather advisory needs of operators of large versus small aircraft or operating aircraft under visual flight rules (VFR) versus instrument flight rules (IFR) are no longer clear. What is increasingly clear is that operators of large aircraft need to receive information pertinent to their operational concerns and that the information intended particularly for operators of small aircraft must receive the widest possible dissemination.
The In-flight Aviation Weather Advisory program has been updated to address these problems and to deal more effectively with the overlapping requirements of different users. In addition, modifications are made to emphasize the distinction between what is meant by forecasts of phenomenon intensities and how encounters with such conditions may be reported by aircrews.
AIRMETs are advisories of significant weather conditions but describe conditions at lower intensities than those that require SIGMETs. The AIRMET portion of the program has been extensively revised to provide continuous scheduled issuances and to emphasize that AIRMETs are as important to aviation safety as nonconvective SIGMETs. Both are intended for dissemination to all pilots in the preflight and the en route phases of flight to enhance safety. Both are intended for use by pilots and aircraft operators as appropriate to their operating environment and individual requirements.
The Federal Aviation Administration (FAA) communications system headers (location identifiers and product-type designators) are used for the examples in this chapter. For the World Meteorological Organization (WMO) and the NWS's Automation of Field Operations and Services (AFOS) communications systems headers, see section 10.
2.1 SIGMET. A SIGMET contains information on specified weather phenomena of an intensity and/or extent that concerns pilots and operators of all aircraft. When weather conditions meeting or exceeding a criterion for SIGMET issuance occur or are expected to occur within 2 hours, a SIGMET shall be issued regardless of whether the conditions are described in the Area Forecast(s) (FA) covering the SIGMET area.
In the conterminous United States, SIGMETs have been separated into two classes, convective and nonconvective.
2.1.1 Convective SIGMET (WST) in the Conterminous United States. WSTs concern only thunderstorms and related phenomena (tornadoes, heavy precipitation, hail, and high surface winds) over the conterminous United States and imply the associated occurrence of turbulence, icing, and convective low level wind shear (LLWS). They are issued hourly and are valid for up to 2 hours. Each hourly issuance supersedes and cancels the remainder of the previous issuance. Appended to each WST bulletin is an Outlook valid for the period from 2 to 6 hours after the issuance time of the SIGMET.
2.1.2 Nonconvective SIGMET (WS1 in the Conterminous United States. WSs are valid for up to 4 hours over the conterminous United States and concern turbulence, icing, dust, sand, volcanic eruptions, or volcanic ash when of sufficient intensity and areal extent.
2.1.3 SIGMETs in Alaska, Hawaii, and Puerto Rico. SIGMETs in Alaska, Hawaii, and Puerto Rico are issued in international formats, in accordance with WSOM Chapter D-38, for both convective and nonconvective weather phenomena and are normally valid for up to 4 hours.
2.2 AIRMET. AIRMETs (WA) may be of significance to any pilot or aircraft operator and are issued for all domestic airspace. Scheduled AIRMET issuances and amendments describe phenomena the same as, or similar to, those requiring the issuance of nonconvective SIGMETs but at lower thresholds. They are of particular concern to operators and pilots of aircraft sensitive to the phenomena described and to pilots without instrument ratings.
WAs are issued every 6 hours, with the first valid period beginning at 0200 Coordinated Universal Time (UTC or Z in aviation products), valid for 6 hours, and describe turbulence, icing, sustained surface winds greater than 30 knots, ceilings below 1,000 feet and/or surface visibilities below 3 statute miles, and mountain obscuration when of sufficient values or intensity and/or areal extent. Amendments are issued as necessary to describe the conditions not originally forecast or the cessation of conditions meeting AIRMET criteria.
3. Responsibility for Issuance. Responsibility for issuance of In-flight Aviation Weather Advisories for conditions over domestic airspace is assigned to several NWS facilities. The National Aviation Weather Advisory Unit (NAWAU) in Kansas City, Missouri, has the responsibility for issuing WAs, WSTs, and WSs for the conterminous United States. The Weather Service Forecast Offices (WSFO) at Anchorage, Fairbanks, and Juneau, Alaska, are responsible for issuing International SIGMETs and WAs for designated Flight Information Regions (FIR) in and around Alaska. The WSFO in Honolulu, Hawaii, issues WAs and International SIGMETs for the Hawaiian domestic airspace (see WSOM Chapter D-20) and International SIGMETs for the Hawaiian portion of the Oakland Oceanic FIR.
The specific domestic airspace areas of responsibility for the various issuing facilities are the same as those described in WSOM chapter D-20.
The designated forecaster(s) at each facility shall maintain a watch on weather developments making use of weather radar, surface observations, pilot reports, and satellite image information. Forecasters should also use available guidance material received from the National Meteorological Center (NMC), products issued by the NMC's National Severe Storms Forecast Center, hurricane advisories issued by the National and Central Pacific Hurricane Centers, forecasts from WSFOs, forecasts and information from the CWSUs, and any other pertinent information as appropriate, in formulating their advisories.
a. All heights or altitudes shall be stated with reference to "mean sea level" (MSL), except in the case of low ceilings which shall be referenced to "above ground level" (AGL) and indicated by "CIGS," e.a., CIGS BLO 10.
b. Domestic In-flight Advisories shall describe designated weather conditions up to and including 45,000 feet (150 millibars).
c. Any abbreviations or contractions used in the advisories shall conform with FAA Contractions Handbook 7340.1 except as noted in section d below.
d. Weather and obstructions to visibility shall be indicated by using the weather abbreviations used for surface airways observations (see Federal Meteorological Handbook No. 1, Surface Observations). Exceptions are detailed in section 8.2 of this chapter.
5. Convective SIGMETs. WSTs are bulletins (collections of one or more products) issued hourly for thunderstorms and related phenomena. Since it is assumed that thunderstorms described in a WST are likely to be accompanied by severe or greater turbulence, severe icing, and low-level wind shear, these conditions shall not be specified in the advisory. The word "none" shall be sent as the text of each hourly WST when the forecaster determines that there is no need for a WST in the designated region (see section 5.3.6).
WSTs shall be issued when either of the following occurs and/or is forecast to occur for more than 30 minutes of the valid period regardless of the size of the area affected (i.e., including isolated):
-severe thunderstorm(s)
- embedded thunderstorm(s).
WSTs shall also be issued when, during the valid period, either of the following criteria occur or are forecast to occur:
- a line of thunderstorms
- an area of active thunderstorms affecting at least 3,000 square miles.
WSTs for severe thunderstorms may include specific information on tornadoes and/or the occurrence of hail of 3/4-inch or greater diameter and/or wind gusts of 50 knots or greater. Tornadoes, 3/4-inch hail or wind gusts to 50 knots or greater alone are sufficient criteria for issuing a WST for severe thunderstorms.
Embedded thunderstorms, for the purpose of WSTs, are defined as thunderstorms occurring within and obscured by haze, stratiform clouds, or precipitation from stratiform clouds. WSTs for embedded thunderstorms are intended to alert pilots that avoidance by visual or radar detection of the thunderstorm could be difficult or impossible.
A line of thunderstorms is defined, for WSTs, as being at least 60 miles long with thunderstorms affecting at least 40 percent of its length.
Active thunderstorms are defined, for WSTs, as thunderstorms having a VIP level (i.e., reflectivity intensity) of 4 or greater and/or having significant satellite signatures and affecting at least 40 percent of the area outlined.
WST issuances are based upon the above criteria and thresholds plus the judgment of the forecaster. For example, the forecaster may decide that the issuance of a WST would be prudent in cases where convective activity does not meet, but is expected to approach, the thresholds. The forecaster must also exercise judgment in determining when the thresholds for meeting these issuance criteria have been (or will be) exceeded.
5.1 Convective SIGMET Bulletins. Three WST bulletins, describing conditions in the eastern (E), central (C), and western (W) regions of the United States, respectively, shall be issued each hour at 55 minutes past the hour (H+55). Special WSTs shall be issued as required. WSTs are stored as replaceable bulletins.
The boundaries between the three regions are at 87 and 107 degrees west. When WST conditions overlie these boundaries, the forecaster shall decide how the WSTs shall be designated for distribution to appropriate facilities and communications circuits by the use of the regional suffixes E, C, or W. The decision on which region to designate shall be based on where the bulk of the observed and forecast conditions are located with respect to the boundary. For example, if most of the WST criteria conditions are located in the Central Region but extend into an overlap area in the Eastern Region, the WST shall have an MKC header. If the majority of the area affected is forecast to move rapidly into the Eastern Region, a WST with the MKCE heading would be issued. In rare cases, when the system is massive enough to extend past the adjacent overlap areas, the same WST may have to be issued for two regions. The overlap areas are:
a. For the boundary at 87 degrees, approximately from 83 to 92 degrees west longitude.
b. For the boundary at 107 degrees, approximately from 103 to 109 degrees west longitude.
Each WST bulletin shall be made up of one or more individually numbered WSTs for conditions within the region and valid for up to 2 hours or until superseded by the next hourly issuance.
5.2. Convective SIGMET Header. The WST product header consists of the 4 lines described below. The communications header on line 1 shall appear only once at the beginning of each individual bulletin. Lines 2, 3, and 4 shall be included in all individual WSTs within the bulletin.
Line 1 - MKCx WST ddtttt
x = E - East of 87 degrees west longitude
C - Central, from 87 degrees west to 107 degrees west longitude
W - West of 107 degrees longitude
dd = Day of month (e.g., 02 or 31) tttt = Issuance time (H+55) in UTC.
Line 2 - CONVECTIVE SIGMET nnx
nn = Issuance Number nn - Individual SIGMETs which make up each bulletin (i.e., MKCE, MKCC, MKCW) shall be numbered consecutively, (e.g., 1-99), each day, beginning at 0000Z. x = C-central, E-eastern, or W-western.
Line 3 - VALID UNTIL hhmmZ
hhmmZ = Product expiration time in UTC.
Line 4 - States or Areas Affected - use the two-letter state, Great Lakes, and state coastal water identifiers detailed in WSOM Chapter D-20, (e.g., KS OK, LM WI LS, or LA CSTL WTRS).
5.3 Convective SIGMET Contents. The contents (after specifying information required on lines 2 through 4) of each individual WST message issued for a SIGMET criterion consists of the location (line 5) and text (line 6). The location shall be described using one or more authorized advisory location identifiers (LOC) shown in exhibit D-22-1. LOCs are the three letter FAA codes of either Very High Frequency (VHF) Omnidirectional Range (VOR) navigational facilities or airports. The text consists of an observation including a 2-hour trend forecast and remarks. It is a description of phenomena compiled from radar reports, satellite data, Pilot Reports (PIREP), or other reports which satisfy the following issuance criteria
5.3.1 Isolated Severe/Embedded Thunderstorms. For isolated severe thunderstorm(s) or embedded thunderstorm(s) of any intensity:
Line 5 - Location - VCNTY LOC or distance and direction LOC (AREA Dxx)
LOC = Selected VORs or airport location identifiers Dxx = Area diameter. (Not to exceed 30 miles.)
Example: VCNTY GCK or 10NE OMA AREA D20
Two or three isolated thunderstorms may be described in one WST if they are closely associated and the text applies to all.
Line 6 - Text - (Intensity trend), ISOLD SVR or ISOLD EMBDD (as applicable), TSTM(s), (Dxx), MOVG FROM ddff. TOP(S) hhh/TO hhh (if 45,000 feet or less)/ABV 450 (if above 45,000 feet. Remarks.
/wsom/manual/IMAGES/d221.gif
Exhibit D-22-1: In-flight Advisory Plotting Chart
Intensity trend = DMSHG (weakening), DSIPTG (ending), INTSFYG
(strengthening), or DVLPG (beginning/growing). Little change shall
be indicated by not using an intensity trend.
Dxx = Cell diameter where xx is in nautical miles.
dd = Direction in tens of degrees.
ff = Speed in knots.
hhh = Height in hundreds of feet as indicated by radar, PIREPs, or
satellite.
The observed or forecast phenomenon which meets the severe thunderstorm criteria should be stated in remarks (i.e., tornado, hail 3/4-inch or greater, or winds, including gusts of 50 knots or greater). Use the following remarks if applicable.
For observed phenomena:
a. TORNADO RPRTD/INDCD ttttZ VCNTY LOC or TORNADO RPRTD/INDCD ttttZ xxxDD LOC (Where ttttZ = time tornado reported or indicated, xxx = distance in nautical miles, and DD = direction on a 16-point compass. See example in section 5.3.4.
b. HAIL TO xx IN RPRTD (Where xx = size in inches and/or fractions of inches).
c. WIND GUSTS TO xxKT RPRTD (xx is speed in knots).
For trend forecast phenomena:
a. TORNADOES...HAIL TO xx IN...WIND GUSTS TO xxKT PSBL.
b. HAIL TO xx IN AND WIND GUSTS TO xxKT PSBL.
c. HAIL TO xx IN PSBL.
d WIND GUSTS TO xxKT PSBL.
e. AREA EXPANDING DDWD (Where DD is a 16-Point compass direction).
f. Any other free format remarks that would, in the forecaster's judgment, add useful information to the product.
Examples: ISOLD EMBDD TSTM D10 MOVG FROM 2520. TOP 300.
ISOLD SVR TSTM D30 MOVG FROM 3430. TOP 450. TORNADO RPRTD 2122Z VCNTY TXK. HAIL TO 1 IN...WIND GUSTS TO 75KT PSBL.
Line 5 - Location of the line - FROM (distance in nautical miles and direction in 16-point compass), LOC- (distance, direction), LOC, etc.
If the phenomenon is located within 5 nautical miles of the LOC location, use the LOC. Describe a line from north to south and west to east, using as many points as are necessary to indicate any changes in line orientation.
Example: FROM 10NE GCK-GAG-1OS AMA
Line 6 - Text - (Intensity trend), LINE, (SVR/EMBDD), TSTMS, (xx MI WIDE), MOVG FROM ddff. TOP(S) hhh/TO hhh (if 45,000 feet or less)/ABV 450 (if tops are above 45,000 feet). Remarks.
Example: LINE SVR TSTMS 25 MI WIDE MOVG FROM 2515. TOPS TO 450. HAIL TO 1-1/2 IN...WIND GUSTS TO 55KT RPRTD.
(See 5.3.1 for intensity trend and forecast remarks.)
Line 5 - Outline of area - FROM, followed by 3 or more xxxDD LOC points starting in the northernmost corner of the area, proceeding clockwise, and ending by repeating the first location.
Example: FROM 90W MOT-GFK-ABR-RAP-9OW MOT
Line 6 - Text - (Intensity trend), AREA, TSTMS/EMBDD TSTMS/SVR TSTMS, MOVG FROM ddff. TOP(S), hhh/TO hhh (if 45,000 feet or less)/ABV 450 (if tops are above 45,000 feet). Remarks.
(See 5.3.1 for observation remarks.)
Example: INTSFYG AREA TSTMS MOVG FROM 2530. TOPS TO 350. HAIL TO 1/2 IN... WIND GUSTS TO 40KT RPRTD. HAIL TO 1 1/2 IN...WIND GUSTS TO 60KT PSBL. AREA EXPANDING NEWD.
5.3.4 Examples. The following are complete examples of WSTs within a bulletin for the central United States.
zCZC
MKCC WST 221855
CONVECTIVE SIGMET l9C
VALID UNTIL 2055Z
OK TX KS
FROM 30E GCK-20E GAG-30E AMA TO DHT TO 30E GCK
LINE TSTMS 25 MI WIDE MOVG FROM 2315. TOPS ABV 450.
CONVECTIVE SIGMET 20C
VALID UNTIL 2055Z
ND SD
FROM 90W MOT-GFK-ABR-RAP-90W MOT
INTSFYG AREA SVR TSTMS MOVG FROM 2530. TOPS ABV 450.
TORNADO RPRTD 1820Z 2ONE RAP. HAIL TP 1/2 IN...WIND GUSTS TO 45KT
RPRTD. TORNADOES...HAIL TO 1 IN...WIND GUSTS TO 65KT PSBL.
NNNN
5.3.5 Special Convective SIGMETs. A WST special shall be issued at any time when either of the following criteria are met and/or forecast to be met for more than 30 minutes of the scheduled WST's valid period:
a. tornado, or hail 3/4-inch or greater, or wind gusts to 50 knots or greater reported to the NAWAU forecaster or indicated when previous WST did not mention severe thunderstorms, or
b. indications of rapidly changing conditions if, in the forecaster's judgment, not sufficiently described in existing SIGMET(s).
Header: tine 1 - MKCx WST ddtttt
x = E, C, or W (see section 5.2) dd = Day of month tttt = Time of issuance (UTC)
Line 2 - CONVECTIVE SIGMET nnx
nn = Issue number incremented from last WST number (hourly or special). For numbers over one hundred, the one is dropped. x = E, C, or W (see section 5.2)
Lines 3-6 See section 5.2 through 5.3.3.
Example: A special WST within a bulletin for the central United States wen the previous hourly WTSs were issued as ...NONE (see section 5.3.6).
ZCZC
MKCC WST 131910
CONVECTIVE SIGMET 21C
VALID UNTIL 2055Z
ND
40W FAR
ISOLD SVR TSTM D30 MOVG FROM 2530. TOP ABV 450. TORNADO RPRTD
1910Z 40W FAR. HAIL TO 2 INWIND GUSTS TO 60KT RPRTD.
When a special WST issuance follows active WSTs issued on the previous hour, the special shall be added to the previous WSTs and shall be the first WST within the bulletin and numbered consecutively after the hourly WSTs.
Example: A special WST within a bulletin for the eastern United States when previous hourly WST(s) were issued.
ZCZC
MKCE WST 131910
CONVECTIVE SIGMET 10E
VALID UNTIL 2055Z
NC
40E CLT
ISOLD SVR TSTM D30 MOVG FROM 2530. TOP ABV 450. HAIL TO 1 IN RPRTD.
CONVECTIVE SIGMET 9E
VALID UNTIL 2055Z
NC SC
FROM RWI-ILM-30S FLO-RWI
AREA SVR TSTMS MOVG FROM 2530. TOP ABV 450. HAIL TO 1 IN RPRTD.
5.3.6 Bulletins for Activity Not Meeting WST Criteria. Since the WST bulletin is a scheduled product, a message must be transmitted each hour. If there are no conditions within a region meeting WST criteria at the scheduled time of issuance, use the following format for transmission.
MKCx WST ddtttt
CONVECTIVE SIGMET NONE
6. Convective SIGMET Outlooks. The Convective SIGMET Outlook is a forecast of thunderstorm conditions beyond the 2-hour valid period of the WST that are expected to meet or exceed WST issuance criteria. This forecast is made each hour and is valid for the period 2 to 6 hours after the issuance time of the WST bulletin to which it is appended. Emphasis is placed on thunderstorms which form lines or active clusters, organized severe thunderstorms, or areas of embedded thunderstorms.
The Convective SIGMET Outlook includes a discussion of the meteorological factors expected to support the convective development which prompted its issuance. Each area detailed shall be a closed outline composed of valid LOCs. Areas overlapping two WST regions follow the same dissemination rules described in section 5.1. A Convective SIGMET Outlook shall always be appended to each scheduled WST bulletin, even if it states "NONE." Negative Outlook statements should be either TSTMS ARE NOT XPCD or TSTMS ARE NOT XPCD TO REQUIRE WST ISSUANCES.
The Outlook has the following format:
OUTLOOK VALID ddtttt-ddtttt (AREA 1) (Lf more than one area is needed) FROM LOC-LOC-LOC-LOC-LOC (using as many LOCs as needed to adequately describe the area). Discussion of criterion(ia) expected to be met and meteorological factors supporting convective development.
AREA N (N = Number of each area as needed) FROM LOC-LOC-LOC-LOC-LOC. Discussion.
Example: A complete WST bulletin, including the Convective SIGMET Outlook, for the Central Region.
MKCC WST 221855 CONVECTIVE SIGMET 20C VALID UNTIL 2055Z ND SD FROM 90W MOT-GFK-ABR-9OW MOT INTSFYG AREA SVR TSTMS MOVG FROM 2445. TOP ABV 450. WIND GUSTS TO 60KT RPRTD. TORNADOES...HAIL TO 2 IN...WIND GUSTS TO 65KT PSBL ND PTN.
CONVECTIVE SIGMET 21C
VALID UNTIL 2055Z
TX
50SE CDS
ISOLD SVR TSTM D30 MOVG FROM 2420. TOPS ABV 450.
HAIL TO 2 INWIND GUSTS TO 65KT PSRL.
OUTLOOK VALID 222055-230055
AREA 1FROM INL-MSP-ABR-MOT-INL
SVR TSTMS CONT TO DVLP IN AREA OVR ND. AREA IS XPCD TO RMN SVR AND
SPRD INTO MN AS STG PVA MOVS OVR VERY UNSTBL AMS CHARACTERIZED
BY -12 LIFTED INDEX.
AREA 2FROM CDS-DFW-LRD-ELP-CDS
ISOLD STG TSTMS WILL DVLP OVR SWRN AND WRN TX THRUT FCST PD AS
UPR LVL TROF MOVS NEWD OVR VERY UNSTBL AMS. LIFTED INDEX RMNS
IN THE -8 TO -10 RANGE. DRY LINE WILL BE THE FOCUS OF TSTM DVLPMT.
7. Nonconvective SIGMETs in the Conterminous United States. Nonconvective SIGMETs for areas within the conterminous United States shall be issued by the NAWAU when any of the following weather phenomena occur or are forecast to occur and affect an area of at least 3,000 square miles.
a. Severe or extreme turbulence or clear air turbulence (CAT) not associated with thunderstorms. (See exhibit D-22-2 and D-22-3.)
b. Severe icing not associated with thunderstorms. (See exhibit D-22-4.)
c. Widespread dust storms, sandstorms, or volcanic ash lowering surface and/or in-flight visibility to less than 3 miles.
d. Volcanic eruption.
7.1 SIGMET Header. The first issuance of any nonconvective SIGMET shall be assigned a UWS (Urgent SIGMET) FAA product type identifier. Any subsequent issuance shall be a WS (SIGMET) unless the forecaster believes the situation warrants using UWS to trigger more expeditious FAA communications handling. Forecaster judgment must be exercised to avoid degrading the value of the UWS message option through overuse.
SIGMETs must be identified accurately to enable proper message distribution and replaceability by communications systems. The key to replaceability is the assignment of unique communications headers. In order to keep the same WS product-type communications designator, replaceability necessitates suffixing a letter (representing the phonetic alphabet series designator) to the area designator. For example, if a SIGMET NOVEMBER 1 is issued, the communications header must be iiiN UWS ddtttt where "N" corresponds to the NOVEMBER series. Only the alphabetic designators NOVEMBER, OSCAR, PAPA, QUEBEC, ROMEO, UNIFORM, VICTOR, WHISKEY, XRAY, and YANKEE shall be used for nonconvective SIGMETs. The permitted alphabetic series designators for SIGMETs exclude those designators reserved for scheduled AIRMETs (SIERRA, TANGO, and ZULU). (See section 8.1.)
In the contiguous states, iii, the area designator (SFO, SLC, CHI, DFW, BOS, MIA) is used to permit selective message distribution within various communications systems. It does not denote the office issuing the forecast. It does denote the geographical area affected (see WSOM Chapter D-20).
Line 1 - Area, alphabetic and message type-designators. and issuance time.
iiix UWS/WS ddtttt
iii = Area designator (SFO SLC CHI DFW BOS MIA)
Exhibit D-22-2: Turbulence Reporting Criteria Table
Exhibit D-22-3: Forecasting Guide on Turbulence Intensity Table
| Intensity | Ice Accumulation | Pilot Report | |
| Trace | Ice becomes perceptible. Rate of accumulation slightly greater than rate of sublimation. It is not hazardous even though deicing/anti-icing equipment is not utilized, unless encountered for an extended period of time-over one hour. | A/C Ident., Location, Time, (GMT) Intensity of type*, Altitude/FL, Aircraft Type, IAS Example: Holding at Westminister VOR, 1232Z Light Rime Icing, Altitude six thousand, Jetstar IAS 200kts |
|
| Light | The rate of accumulation may create a problem if flight is prolonged in this environment (over one hour). Occasional use of deicing/anti-icing equipment removes/prevents accumulation. It does not present a problem if the deicing/anti-icing equipment is used. | ||
| Moderate | The rate of accumulation is such that even short encounters become potentially hazardous and use of deicing/anti-icing equipment or diversion is necessary. | ||
| Severe | The rate of accumulation is such that deicing/anti-icing equipment fails to reduce or control the hazard. Immediate diversion is necessary. | ||
| * Rime Ice: Rough, milky, opaque ice formed by the instantaneous freezing of small supercooled water droplets. Clear Ice: A glossy, clear or translucent ice formed by the relatively slow freezing of large supercooled water droplets. |
|||
Exhibit D-22-4: Airframe Icing Reporting Table
x = N through Y (excluding S and T), denoting the SIGMET's alphabetic series designation UWS = Urgent SIGMET message type designator WS = SIGMET message type dd = Day of month tttt = Issuance and beginning valid time UTC
Example: SFOP UWS 051710
Line 2 - Title, alphanumeric deeignator, and SIGMET expiration time.
SIGMET, Alphanumeric designator, VALID UNTIL ddtttt
Alphanumeric deeignator = An alphabetic designator (NOVEMBER, etc.) and issuance number VALID UNTIL ddtttt = Ending Valid Time
Example: SIGMET PAPA 1 VALID UNTIL 052110
The first time a SIGMET is issued for a phenomenon associated with a particular weather system, it shall be given the next alphabetic designator in the series and shall be numbered as the first for that designator, e.g., NOVEMBER 1. It shall be numbered consecutively, using the same designator, i.e., NOVEMBER 2, NOVEMBER 3, etc., until the phenomenon ends or no longer meets SIGMET criteria.
In the conterminous United States, this means that a phenomenon that is assigned an alphabetic designator in one area shall retain that designator as it moves within the area or into one or more other areas. For example, the first issuance for a continuing phenomenon which has moved into the CHI area from the SLC area might be SIGMET OSCAR 4. While this SIGMET OSCAR 4 is indeed the first SIGMET issued for this phenomenon in the CHI area, it is actually the fourth issuance for the phenomenon since it met SIGMET criterion with the previous three issuances having occurred over the SLC area.
To alert users that a SIGMET, CHI SIGMET OSCAR 4 in this case, is the first issuance for an area, a referencing statement shall be included after the last remark, e.g., FOR PREVIOUS ISSUANCE SEE SLC SIGMET OSCAR 3. SIGMETs for separate phenomena shall be designated sequentially, i.e., NOVEMBER, OSCAR, PAPA, etc., through YANKEE, and all designators through YANKEE, except SIERRA, TANGO, AND ZULU, shall be used before starting all over again with NOVEMBER. All six FA areas shall use the same alphabetic series.
While SIGMETs may be issued up to 2 hours before the onset of any condition forecast to meet a criterion, note that the time in line 1 is the issuance time (rather than the onset time) and the time indicated in the VALID UNTIL ddtttt statement is the SIGMET expiration time. The difference between the two must not exceed 4 hours. For example, a SIGMET issued at 0210Z (0210 and 0610 entered as tttt on lines 1 and 2, respectively) and expected to persist beyond 4 hours shall include a statement in the remarks of the text indicating that conditions are expected to continue and/or spread after the 4-hour SIGMET period ends. If conditions persist, the next SIGMET should be issued before the expiration time of the previous SIGMET. However, if conditions end, a SIGMET cancellation shall be transmitted. SIGMETs for conditions which end within one-half hour of the "VALID UNTIL" time, which do not state conditions will continue, may be allowed to expire without cancellation. When a SIGMET condition is expected to last less than 4 hours, the expected ending time of the SIGMET condition shall be indicated in the "valid until ddtttt" statement. A SIGMET cancellation shall be issued if the condition ends more than 1/2-hour prior to that expiration time. Caution must be used concerning SIGMETs with valid times of less than 4 hours. Some action, either a reissuance or cancellation, usually must be taken before the valid period expires.
Line 3 - States or Areas Affected. Use two-letter state, Great Lake, and coastal water identifiers, e.g., MI, WV, LE, or TX LA CSTL WTRS.
Example: DFWP UWS 051710
SIGMET PAPA 1 VALID UNTIL 052110
AR LA MS AND CSTL WTRS
Line 4 - Location of phenomena. FROM (distance in nautical miles and direction in 16-point compass), LOC (see section 5.3 and exhibit D-22-1), TO (distance, direction), LOC, etc.
Example: FROM MEM TO 30N MEI TO BTR TO MLU TO MEM
Use the minimum number of points necessary to accurately enclose the area of a SIGMET phenomenon. The area should be delineated by starting in the northernmost corner of the area, proceeding clockwise, and ending with the first point.
7.1.2 Multiple Area Designators. Since all SIGMETs in the conterminous United States are issued from the NAWAU in Kansas City, the points describing the location of a phenomenon meeting SIGMET criteria may extend beyond the boundaries for the area designator under which the SIGMET is issued. This is encouraged to avoid truncated delineation of weather areas. When a SIGMET criteria phenomenon extends or is forecast to extend across FA region boundaries, the phenomenon shall be described and its location coordinated across the boundaries as if no FA region boundaries exist. Then, the description and location shall again be coordinated to use the minimum number of LOCs or reference points necessary to enclose the phenomenon within each of the affected FA region boundaries. The same coordinated LOC boundaries shall be used in each FA region for which the SIGMET is issued. This method of describing the phenomenon allows each SIGMET area outline to overlap FA boundaries where necessary.
The two-letter identifier of the state(a) or area(s) within the SIGMET shall be included in the "states or areas affected" line when at least two LOCs used to describe the SIGMET are within the state or a significant portion (e.g., 3,000 square miles or more) of the state or area is affected. In addition, any states in an adjacent FA region(s) that are within an overlapping area outline should be included at the end of the SIGMET's "state(s) or area(s) affected" line if they meet one of the criteria above.
If SIGMETs are issued covering an area in the adjacent FA regions, the description of the conditions should be the same in any common or overlapping areas described in the products.
While this chapter establishes the policy guidelines above, the forecaster's judgment must prevail. Forecasters shall determine when a single SIGMET is appropriate and when multiple SIGMETs are necessary due to the areal coverage of the phenomenon at a given instant and/or the area through which a phenomenon will be moving over time.
Example: Coordinated area meeting SIGMET criteria:
FROM TVC TO ERI TO AND TO MSL TO TVC
Coordinated SIGMET issuances for the affected FA regions:
CHI SIGMET area: HI IN KY OH LE WV
FROM TVC TO ERI TO TRI TO 20W BNA TO TVC
BOS SIGMET area: OH LE WV VA KY
FROM ERI TO TRI TO CVG TO 40NE FWA TO ERI
DFW SIGMET area: TN
FROM TRI TO 20S CHA TO MSL TO 20W BNA TO TRI
MIA SIGMET area: NC TN
FROM TRI TO AND TO 2OS CHA TO TRI
A referencing remark regarding the previous issuances is required in the appropriate message(a) if the SIGMET is not the first issuance for the phenomenon.
It should be noted that for a phenomenon occurring at the juncture of the CHI, BOS, MIA, and DFW areas, four SIGMETs may be in effect at one time with the only difference being the four area designators and the outlines of the areas affected, It is important to note that the alphanumeric designator in this event would be the same for all four SIGMETs.
7.2 Nonconvective SIGMET Message Texts. The following standardized SIGMET formats shall be used for the appropriate SIGMET criterion.
7.2.1 Severe and Extreme Turbulence. SIGMETs for turbulence, including CAT, shall be issued for an area when severe or extreme turbulence is reported or forecast (see exhibits D-22-2 and D-22-3) over an area covering at least 3,000 square miles.
Format: (MDT TO), (OCNL) SVR/EXTRM, TURBC, WITH STG UDDFS/UPDFTS/DWNDFTS (optional), INVOF MTNS (optional), BLO hhh/ABV hhh/BTWN hhh AND hhh, XPCD (DUE TO cause)/RPRTD BY (PIREP). Remarks.
The term "optional" and text elements enclosed in parentheses as used in the above and subsequent formats, indicate that the associated text may be used when appropriate or available, at the discretion of the forecaster. The term "OCNL" is defined as a greater than 50 percent probability of occurrence but that the occurrence shall total less than half of the entire forecast period. "OCNL" should be used when appropriate. with forecasts only, even if PIREPs of occasional turbulence have been received.
hhh = Height in hundreds of feet MSL
Cause = Causal factors
Include the cause only when XPCD is used within the body of the message and if it adds to the understanding of the SIGMET. When RPRTD BY is used in the text, include the pertinent PIREP information in the appropriate section of the fixed format if it helps lend credence to the SIGMET. Otherwise, include one of the following statements: RPRTD BY ACFT IN VCNTY or RPRTD BY SVRL ACFT.
Causal factors include jet streams, mountain wave action, strong fronts, upslope or overrunning clouds or rain, strong low-level wind, etc.
Remarks = Comments which expand or clarify the SIGMET, particularly information concerning onset and cessation of SIGMET conditions. Such information shall be stated using one of the following phrases:
a. CONDS BGNG BY ttttZ
b. CONDS CONTG (location) BYD ttttZ
c. CONDS IPVG TO (conditions) AFT ttttZ
d. CONDS IPVG TO (conditions) OVR location AFT ttttZ
e. CONDS IPVG TO (conditions) FM dd AFT ttttZ
f. CONDS ENDG AFT ttttZ
g. CONDS SPRDG OVR location BY ttttZ
h. CONDS MOVG (direction) THRU ttttZ
Some of the above remarks may be combined, e.g., CONDS BGNG BY 1200Z AND CONTG BYD 1400Z. Location refers to states or portions of states or recognized geographical areas. dd is an area direction (see section 7.2.3).
Examples: MDT TO SVR TURBC BTWN 200 AND 250 RPRTD BY ACFT IN VCNTY. CONDS CONTG BYD 1800Z.
OCNL SVR TURBC WITH STG UDDFS INVOF MTNS BLO 150 XPCD DUE TO MTN WAVES. CONDS IPVG AFT 1800Z.
7.2.2 Clear Air Turbulence (CAT). CAT is defined as turbulence not associated with cumuliform clouds, including thunderstorms, occurring at or above 15,000 feet. SIGMETs for CAT shall be issued when severe or extreme turbulence is reported or forecast over an area covering at least 3,000 square miles, i.e., CAT shall be treated exactly the same as any other category of turbulence. Forecasts of moderate turbulence at any level up to 45,000 feet are included in the turbulence AIRMET bulletins.
7.2.3 Severe Icing. SIGMETs for icing shall be issued for an area when severe icing is reported or forecast (see exhibit D-22-4) over an area covering at least 3,000 square miles.
Format: (MDT TO), (OCNL) SVR icing type (CLR, RIME, MXD) (optional), ICG, BLO hhh/BTWN hhh AND hhh/BTWN.FRZLVL AND hhh, XPCD (DUE TO cause)/RPRTD BY (PIREP). FRZLVL, SFC/hhh/BTWN hhh (dd) AND hhh (dd)/SFC (dd)-hhh (dd)/SFC or hhh (dd) SLPG TO hhh (dd). Remarks (see section 7.2.1).
dd = 8-point compass direction of a portion of the advisory area.
Weather and obstructions to visibility shall be indicated using the same contractions used for surface airways observations. The height of the freezing level shall be included any time the freezing level is referenced.
Examples: SVR CLR ICG BLO 160 RPRTD BY B727. CONDS CONTG BYD 1310Z.
MDT to OCNL SVR ICG BTWN FRZLVL AND 160 XPCD DUE TO COLD ADVCTN AND STG LOW LVL CONVERGENCE. FRZLVL 80 E SLPG TO 120 W. CONDS SPRDG OVR NY NJ CSTL SXNS BY 1000Z.
7.2.4 Widespread Dust Storms. Sandstorms, and Volcanic Ash. SIGMETs for dust storms, sandstorms, or volcanic ash shall be issued when they cause, or are expected to cause, surface or in-flight visibilities to be below 3 miles over an area of at least 3,000 square miles. In the case of volcanic ash, a SIGMET may be issued if the conditions affect any size area which, in the judgment of the forecaster, is significant to aviation operations near that area. The issuance threshold of 3 miles is not used as a threshold between hazardous and nonhazardous conditions. It is the threshold at which reports can be reliably expected. It is also the point at which an operational impact is assured since IFR operations would be required in controlled airspace.
Even when these phenomena result in visibilities greater than 3 miles, they may still constitute an extreme hazard to aircraft operations. SIGMETs should be issued under these conditions when, in the forecaster's judgment, a hazard is known to exist.
Conditions, such as the physical characteristics of the volcanic ash, the remote locations of many volcanoes, and/or the ash being obscured within clouds, may make determining the occurrence of an eruption or the existence of ash aloft difficult, if not impossible. After the first (Urgent) SIGMET for volcanic ash is issued, that SIGMET series should be updated when any information becomes available which will increase the In-flight Advisory's effectiveness.
Formats:
VSBY, BLO/AOB 3 IN, DUST/SAND, BLO hhh/ABV hhh/BTWN hhh AND hhh, XPCD (DUE TO cause)/RPRTD BY (PIREP). Remarks (see section 6.2.1), or
VOLCANIC ASH, BLO hhh/ABV hhh/BTWN hhh AND hhh, XPCD (DUE TO source eruption)/RPRTD BY (PIREP or other observation). Remarks (see section 6.2.1).
Examples: VSBY BLO 3 MI IN DUST BLO 120 RPRTD BY SVRL ACFT. CONDS CONTG BYD 2310Z.
VOLCANIC ASH BTWN 150 AND 250 DUE TO MT. ST HELEN ERUPTION RPRTD BY SVRL ACFT. CONDS SPRDG OVR NW AZ BY 2230Z AND CONTG BYD 2310Z.
7.2.5 Volcanic Eruption. A SIGMET for a volcanic eruption shall be issued as soon as possible after receipt of notification that a volcanic eruption
Example: REPORT RECEIVED THAT MT. ST HELEN ERUPTED AT 1230Z. VOLCANIC CLOUD XPCD TO MOVE NEWD. TOPS OF CLOUD MAY REACH 350. A SIGMET FOR VOLCANIC ASH WILL BE ISSUED AS SOON AS MORE INFORMATION BECOMES AVAILABLE.
Volcanic eruptions may continue for only a short period of time while some may pulse for long periods of time causing significant disruptions to the flow of air traffic. Due to the serious threat volcanic ash poses to aircraft in flight, multiple issuances under a SIGMET series due to repeated and/or ongoing eruptions should be made to advise the aviation community of recurring events regardless of whether or not visibility or "known-hazard" criteria are met. A single, short-lived eruption will result in a single Urgent SIGMET, valid for 4 hours. The alphabetic designator for that SIGMET should not be reused for 24 hours to allow any subsequent eruption notifications to be issued under the same designator.
7.2.6 Relationship of Nonconvective SIGMETs to Tropical Storm and/or Hurricane Advisories. Conditions meeting SIGMET criteria, which result from tropical storms or hurricanes, shall be referenced in the "cause" phrase of the SIGMET as follows (see section 7.2.1).
DUE TO (HURCN ANA, TRPCL STM BOB, etc)...SEE LAmanual ADVY.
7.2.7 SIGMET Cancellations. SIGMET cancellations shall be transmitted, when appropriate, in the following format.
Format: CNCL SIGMET, alphanumeric designator. Remarks.
Example: CNCL S}GMET QUEBEC 1. CONDS HAVE BCM MDT.
DFWP UWS 051700
SIGMET PAPA 1 VALID UNTIL 052100
AR LA MS
FROM MEM TO 30N MEI TO BTR TO MLU TO MEM
MDT TO OCNL SVR ICG BTWN FRZLVL AND 150. FRZLVL 80 E TO 120 W. CONDS CONTG
BYD 2100Z.
SFOX WS 030130
SIGMET XRAY 2 VALID UNTIL 030530
OR WA
FROM SEA TO PDX TO EUG TO ONP TO HQM TO SEA
MDT TO OCNL SVR TURBC BTWN 280 AND 350 XPCD DUE TO WINDSHEAR ASSOCD WITH
JTSTR CONDS BGNG AFT 0200z CONTG BYD 0530Z AND SPRDG OVR CNTRL ID BY 0400Z.
Example of a multiarea issuance SIGMET:
CHIO WS 051700
SIGMET OSCAR 2 VALID UNTIL 052100
KS
FROM PWE TO OSW TO 40W LBL TO PWE
OCNL SVR TURBC BLO 60 XPCD DUE TO STG NWLY FLOW BHD CDFNT. CONDS CONTG BYD
2100Z.
DFWO WS 051700
SIGMET OSCAR 2 VALID UNTIL 052100
OK KS
FROM OSW TO ADM TO 40W LBL TO OSW
OCNL SVR TURBC BLO 60 XPCD DUE TO STG NWLY FLOW BHD CDFNT. CONDS CONTG BYD 2100Z
Example of a multiarea issuance SIGMET canceled in one area and continued in another
CHIO WS 052100
CANCEL SIGMET OSCAR 2, CONDS HAVE DMSHD.
DFWO WS 052100
SIGMET OSCAR 3 VALID UNTIL 060100
OK
FROM OSW TO TXK TO SPS TO GAG TO OSW
OCNL SVR TURBC BLO 60. CONDS ENDG AFT 00Z.
8. AIRMETs. AIRMETs are also advisories of significant weather phenomena but describe conditions at intensities lower than those which trigger SIGMETs. Both are intended for dissemination to all pilots in the en route phase of flight to enhance safety.
AIRMET bulletins, each containing one or more AIRMET messages, shall be issued on a scheduled basis every 6 hours with 0200 UTC as the first valid time. Unlike FAs, scheduled AIRMET bulletin issuances shall occur at the same UTC times regardless of their area designators. Unscheduled amendments and corrections will be issued as necessary. AIRMET bulletins shall contain details of conditions within their designated geographical areas when one or more of the following conditions occurs, or is expected to occur, and affect an area of at least 3,000 square miles:
a. Moderate icing
b. Moderate turbulence
c. Sustained surface wind of 30 knots or more
d. Ceilings less than 1,000 feet and/or visibility less than
3 miles affecting over 50 percent of an area at any one time
e. Extensive mountain obscuration
8.1 AIRMET Header. As with SIGMETs, AIRMETs must be identified accurately to enable proper message distribution and replaceability within communications systems. The key to AIRMET selective replaceability is the assignment of unique communications headers for each phenomenon type. In order to use the same WA product-type communications designator, a letter (reflecting the alphabetic designator of the phenomenon to be described) must follow the area designator. For example, when the AIRMET for turbulence is issued, the communications header must be iiiT WA ddtttt where "T" (for TANGO) is the alphabetic designator for turbulence AIRMET bulletins.
In the contiguous states, the iii (SFO, SLC, CHI, DFW, BOS, MIA) is used for message distribution in the communications systems and does not denote the office issuing the forecast, although it does denote the geographic area affected (see WSOM Chapter D-20). In Alaska and Hawaii, each iii does denote the issuing office.
Line 1 - Area, phenomenon and message type designators, and date-time group.
iiix WA dUtttt (AMD/COR #)
iii = SFO, SLC, CHI, DFW, BOS, MIA, ANC, FAI, JNU, HNL
x = The alphabetic phenomenon designation of AIRMET bulletins; S for
significant IFR or mountain obscuration, T for turbulence, strong
surface winds, or LLWS, and Z for icing and freezing level.
WA = AIRMET message type designator.
dd = Day of month.
tttt = Issuance time (UTC). Scheduled issuance times are 15 minutes
prior to the beginning of the valid period. Amended and corrected
bulletins issued after the start of the valid period are valid
beginning at the time of issuance.
AMD/COR = Indicator that AIRMET bulletin is an amendment or
correction to a scheduled issuance.
# = Amendment or correction number since the last scheduled issuance.
Example: DFWZ WA 181525 AMD 1
Line 2 - AIRMET, phonetic alphabet phenomenon designator, FOR criteria, VALID UNTIL ddtttt
Phonetic alphabet phenomenon designators = SIERRA, TANGO, or ZULU Criteria = The primary phenomenon indicated by the designator and any additional designated phenomena actually contained in the bulletin, e.g., mountain obscuration or strong surface winds. VALID UNTIL ddtttt = Valid period expiration time. This shall be 6 hours after the scheduled ''valid beginning" time or 6 hours and 15 minutes after the scheduled issuance time.
Example: AIRMET TANGO FOR TURBC...STG SFC WINDS AND LLWS VALID UNTIL 182000 (NOTE: The three dots in this example are equivalent to a comma.)
The contents of AIRMET bulletin lines following line 2 will vary depending on conditions. To aid automatic processing of the products, each subsequent line or section shall be preceded by a line containing only a period (.) as a delimiter.
As a minimum, each AIRMET bulletin shall contain lines 1 and 2 and the statement "NO SGFNT, Standard criteria, XPCD." on line 3. In addition, icing and freezing level AIRMETs shall contain a freezing level line.
Example: NO SGFNT ICG XPCD
FRZLVL...100-130 THRUT.
Other options for line 3 are as follows.
Whenever SIGMETs are in effect, the AIRMET bulletins for the same phenomena, which cover the affected area(s) shall contain a reference to the appropriate SIGMET series. This reference, when required, shall be line 3 of the AIRMET bulletin.
Line 3 - ...SEE SIGMET Alphabetic designator SERIES FOR (appropriate phenomenon)
Examples: ...SEE SIGMET XRAY SERIES FOR SVR TURBC AREA...
...SEE SIGMET WHISKEY SERIES FOR IFR VSBY/HAZUS VOLCANIC ASH AREA...
This results in the displacement of all other line 3 and subsequent line entries by one line. All AIRMET formats and examples shown in this chapter are numbered as if this option has not been used.
All conditions within a designated geographical area which meet AIRMET criteria for a phenomenon shall be described in the AIRMET bulletin for that area and phenomenon. Each area or meteorologically distinct set of conditions shall be described in a separate message prefixed by the word AIRMET and a list of states and/or geographical area(s) (or, in Alaska and Hawaii, geographical sections or islands) affected (see section 5.2).
Line 3 - (AIRMET, phenomenon,...states/areas/sections/islands affected.) Use two-letter state, Great Lake, and coastal water identifiers, e.g., MI, WV, LE, and TX CSTL WTRS, and authorized contractions or plain language for the names of geographical sections and islands.
Examples: AIRMET IFR...AR LA MS AND LA MS AL CSTL WTRS
AIRMET TURBC...SRN SEWARD PEN AND ERN NORTON SOUND
In addition, turbulence and icing conditions not meeting AIRMET criteria due to intensity (such as light icing) or area coverage (such as local), which in the forecaster's judgment are significant to some flight operations, should also be described. Such conditions shall not have the word AIRMET or a list of states or areas affected as a prefix. However, states or areas affected should be detailed in the text to identify the area of concern.
When there are no areas of conditions meeting AIRMET icing or turbulence criteria but non-AIRMET conditions are deemed significant by the forecaster, line 3 of the AIRMET header shall be used to describe those conditions, thus becoming the AIRMET bulletin text.
Line 3 - Significant non-AIRMET criteria icing or turbulence description and location
Example: OCNL LGT LCL MDT TURBC BLO 100 OVR SRN CA MTNS WITH NLY SFC WNDS 25KT
When AIRMET criteria are met, line 4 of the bulletin header and the second line of each subsequent AIRMET shall contain a list of LOCs outlining the area expected to be affected during the valid period of the AIRMET. In Alaska and Hawaii, the forecaster may also use the geographic areas as specified in WSOM Chapter D-20 and other well-known geographic identifiers (e.g., the Alaska Range) to describe the location of the phenomenon.
Line 4 - Location of phenomenon--FROM (distance in nautical miles and direction in 16-point compass), LOC (see section 5.3 and exhibit D-22-1), TO (distance, direction), LOC, etc.
Example: FROM MEM TO MSL TO 50S MSY TO LCH TO MEM
Use the minimum number of points necessary to accurately outline the area of an AIRMET phenomenon. The area should be delineated by starting in the northernmost corner of the area, proceeding clockwise, and ending with the first point.
8.1.2 Multiple Area Designation. As in the case of SIGMETs, the points describing the location of phenomenon meeting AIRMET criteria may extend beyond the boundaries of the area designator under which the AIRMET bulletin is issued. This is encouraged to avoid truncated delineations of weather areas.
When an AIRMET criteria phenomenon extends or is forecast to extend across FA region boundaries, the phenomenon shall be described and its location coordinated across the boundaries as if no FA region boundaries exist. Then the description and location shall again be coordinated to use the minimum number of LOCs or reference points necessary to accurately enclose the phenomenon within each of the affected FA region boundaries. The same coordinated LOC reference points defining the location of the phenomenon at the FA region boundaries shall be used in each FA region for which the AIRMET is issued. This method of describing the phenomenon allows each AIRMET area to overlap FA boundaries where necessary.
The two-letter identifier of the state(s) or area(s) within the AIRMET area outline shall be included in the "states or areas affected" line when at least two LOCs used to describe the outline are within the state, or, when a significant portion (e.g., 3,000 square miles or more) of the state or area is within the outlined area. In addition, any states in an adjacent FA region(s) that meet either of the above tests should be included at the end of the AIRMET's "state(s) or area(s) affected" line.
If AIRMETs are issued for an area in multiple FA regions, the description of the condition" should be the same in any common or overlapping areas described in the products.
Example: Coordinated area meeting AIRMET criteria:
FROM TVC TO ERI TO AND TO MSL TO TVC
Coordinated AIRMET issuances for the FA regions:
CHI AIRMET area: MI IN KY OH LE WV
FROM TVC TO ERI TO TRI TO 20W BNA TO TVC
BOS AIRMET area: OH LE WV VA KY
FROM ERI TO TRI TO CVG TO 40NE FWA TO ERI
DFW AIRMET area: TN
FROM TRI TO 20S CHA TO MSL TO 20W BNA TO TRI
MIA AIRMET area: NC TN
FROM TRI TO AND TO 20S CHA TO TRI
A referencing remark regarding previous issuances may be included in the appropriate message(s) if the AIRMET is not the first issuance for the phenomenon.
It should be noted that for a phenomenon occurring at the juncture of the CHI, BOS, MIA, and DFW areas, four AIRMETs may be in effect at one time with the only difference being the four area designators and the area outlined.
8.2 AIRMET Message Texts. The text portion of each AIRMET message within a bulletin shall contain the available details about the phenomenon conditions which have met or are expected to meet AIRMET or significance criteria. These details shall include conditions that are occurring or forecast to occur, their causes, their vertical extent, any changes expected during the AIRMET valid period, and remarks concerning the time of onset and/or cessation of conditions.
If the phenomenon is not expected to end during the valid time of the AIRMET bulletin, the continuance of the conditions shall be described in the remarks section of the text as much as practicable. If more detail is needed to describe the continuance of existing conditions and/or for development of conditions after the first 6 hours valid time of the AIRMET, there shall be an outlook paragraph immediately following the AIRMET text valid for the 6 hours beginning at the AIRMET ending time. This outlook paragraph shall include the states or areas affected followed by a general description of the conditions as they are expected to continue, develop, move, and/or end during that 6hour outlook period.
Weather and obstructions to visibility described as causes shall be indicated using the same contractions used for surface airways observations. Generic causes (e.g., "precipitation") shall only be used where the words "IN" or "BY" are included in the format and should normally be contractions of words instead of observation contractions. For example, VSBY BLO 3 IN SHWRS AND TSTMS or MTNS OBSCD BY DRZL AND FOG.
When RPRTD BY is used in the text, include the pertinent PIREP details in the appropriate portion of the fixed format if it helps to lend credence to the AIRMET. Otherwise, include one of the following statements: RPTRD BY ACFT IN VCNTY or RPTRD BY SVRL ACFT.
Only the following phrases shall be used as remarks concerning onset and cessation of AIRMET conditions.
a. CONDS BGNG BY ttttZ
b. CONDS CONTG (location) BYD ttttZ
c. CONDS IPVG TO (conditions) AFT ttttZ
d. CONDS IPVG TO (conditions) OVR location AFT ttttZ
e. CONDS IPVG TO (conditions) FM dd AFT ttttZ
f. CONDS ENDG AFT ttttZ
g. CONDS SPRDG OVR location BY ttttZ
h. CONDS MOVG (direction) THRU ttttZ
Some of the above remarks may be combined, e.g., CONDS BGNG BY 1200Z AND CONTG BYD 1400Z. Location refers to states or portions of states or recognized geographical areas. dd is an area direction (see section 7.2.3).
Forecasters shall use a combination of scheduled AIRMET messages and amendments to describe the unexpected onset or cessation of conditions meeting AIRMET criteria. For example, an AIRMET valid at 0200Z (0145 and 0800 entered on lines 1 and 2 respectively) contains an outlook for conditions expected to move into the designated region and/or expand after 0800Z. The message shall include a statement in the remarks of the text indicating that conditions are expected to begin after the end of the 6-hour period and/or spread. If conditions begin prior to the next scheduled issuance of AIRMET bulletins, an amendment to the appropriate bulletin(s) shall be issued adding a message for the area which now meets AIRMET criteria and repeating all previous messages still in effect.
8.2.1 AIRMET Cancellations. AIRMET cancellations shall be transmitted when appropriate in the following manner. When an AIRMET condition is expected to last 6 hours or less, the expected ending time of the AIRMET condition should be stated in the remarks portion of the text. When an AIRMET condition is expected to begin and end within the valid period of the bulletin, the period when the phenomenon is expected shall be stated in the text (e.g., VSBYS BLO 3F BTWN 0300 AND 0700Z). If conditions end more than 1 hour prior to the stated end-time or if no time was stated, prior to the "VALID UNTIL" time, an amended AIRMET bulletin, containing an AIRMET message cancellation and any previously issued messages still in effect, shall be transmitted. If the conditions end within an hour of the ending time stated in the bulletin, the bulletin is allowed to expire without cancellation.
Example: SFOS WA 191200 AMD 1
AIRMET SIERRA FOR IFR AND MTN OBSCN VALID UNTIL 191400
AIRMET IFR...CA CSTL WTRS...AMD 1
FROM SBA TO LAX TO SAN TO 120SW SAN TO 100W SBA
TO SBA CNCL AIRMET. CONDS HAVE BCM LCL.
AIRMET MTN OBSCN...CA
FROM LAX TO 30N SAN TO 30S SAN TO LAX
MTNS OCNL OBSCD. CONDS ENDG BY 1400Z.
The following subsections detail the standardized formats which shall be used for the indicated AIRMET criterion.
Format: (LGT TO), OCNL MDT/MDT TURBC, WITH UDDFS/UPDFTS/DWNDFTS (optional), INVOF MTNS (optional), BLO hhh/ABV hhh/BTWN hhh AND hhh, XPCD (BTWN tt AND ttZ) (DUE TO cause)/RPRTD BY (PIREP). Remarks.
hhh = Height in hundreds of feet MSL
Cause = Causal factors
Include the cause only when XPCD is used within the body of the message and if it adds to the understanding of the AIRMET. Causal factors include jet stream, mountain wave action, strong fronts, upslope or overrunning clouds or rain, strong low-level wind, etc.
Examples: OCNL MDT TURBC BLO 80 XPCD. CONDS CONTG BYD 1400Z AND SPRDG OVR NRN SD SWRN MN.
MDT TURBC BLO 100 RPRTD BY SVRL ACFT. CONDS IPVG AFT 2100Z.
8.2.3 Strong Surface Winds. "Strong Surface Winds" are defined in this paragraph as sustained surface winds 30 knots or greater. If sustained surface winds 30 knots or greater are expected, line 2 of the AIRMET bulletin header shall contain the statement "FOR TURBC AND STG SFC WNDS VALID UNTIL ddbttt
Format: SUSTAINED SFC WNDS GTR THAN 30KT, XPCD (BTWN tttt AND ttttZ) (DUE TO Cause)/RPRTD/RPRTD BY (PIREP). Remarks.
Example: SUSTAINED SFC WNDS GTR THAN 30KT RPRTD. CONDS ENDG AFT 1600Z.
8.2.4 Nonconvective LLWS Potential. When nonconvective LLWS (wind shear below 2,000 feet AGL) is affecting or expected to affect an area of at least 3,000 square miles, the turbulence AIRMET bulletin shall include an LLWS potential statement as a separate message.
Forecasters should include as much information about LLWS as they feel reasonably sure of. Experience has shown that the precise vertical wind profile is rarely known during a wind-shear event, and thus, an exact wind normally would not be included. The following format should be used when LLWS is expected.
LLWS POTENTIAL (location--states, areas or LOCs), time (if applicable), DUE TO/ASSOCD WITH (cause). (remarks).
examples: a. Warm Front
LLWS POTFNTIAL LO NY TIL 02Z ASSOCD WITH STG WRMFNT MOVG N OVR AREA.
b. Cold Front
LLWS POTENTIAL KS IA MO BTWN 18-OOZ ALG AND 50 MI NW STG CDFNT.
c. Low-Level Jet and Nocturnal Inversion LLWS POTENTIAL ACRS SERN NE ERN KS IA NWRN MO TIL 06Z DUE TO LOW-LVL JET AND NIGHTTIME INVRN.
d. Cold-Surface Inversion
LLWS POTENTIAL CA W CST MTNS FROM 10Z TO 17Z ASSOCD WITH MRTM INVRN.
e. Friction-Surface Slowing
LLWS POTENTIAL OVR NEW ENG CSTL SXNS AFT 16Z DUE TO STG NWLY LOW LVL
FLOW BHND CDFNT.
f. Nocturnal-Valley Inversion
LLWS POTENTIAL SW MT VLYS AFT 06Z DUE TO STG NIGHTTIME INVRN AND
I CRG SWLY FLO ALF.
g. Sea Breeze Front
LLWS POTENTIAL GA AND NERN FL CSTL SXNS 18-23Z DUE TO SEA BREEZE FNT.
Format: (LGT TO), (OCNL) MDT, Icing type (CLEAR, RIME, MIXED) (optional), ICG, BLO hhh/ABV hhh/BTWN hhh AND hhh/ABV FRZLVL/BTWN FRZLVL AND hhh, XPCD (BTWN tt AND ttZ) (DUE TO cause)/RPRTD BY (PIREP). Remarks.
FRZLVL...SFC/hhh/SFC-hhh/BTWN hhh AND hhh/SFC or hhh SLPG TO hhh.
Examples: OCNL MDT ICG BLO 80 XPCD DUE TO WDSPRD S AND ZR N AND E OF WRMFNT. CONDS BGNG AFT 1000Z AND ENDG BY 1400Z.
MDT MXD ICG BTWN 75 AND 100 RPRTD BY ACFT IN VCNTY. CONDS CONTG BYD
2000z
8.2.6 IFR Ceilings and/or Visibility. When either ceilings or surface visibility are or are expected to be less than 1,000 feet or 3 miles over an area of at least 3,000 square miles, a description of the area and conditions shall be included in the IFR AND MTN OBSCN AIRMET bulletin. Since conditions for ceilings below 1,000 feet and/or visibilities below 3 miles are no longer included in the FA (see WSOM Chapter D-20), as much detail as possible should be included in the AIRMET SIERRA bulletin. Forecasters should specify the IFR ceilings and/or visibility when able.
Formats: (OCNL) CIG (BLO 10) or (AOB hh) (AND/or) VSBY (BLO 3) or (AOB v) (weather or obstruction to visibility cause), (XPCD) (BTWN tttt AND ttttZ) (IN phenomenon)/RPRTD BY (PIREP). Remarks.
(OCNL) CIGS/VSBYS BLO 10/3, (XPCD) (BTWN tttt AND ttttZ) (IN phenomenon)/RPRTD BY (PIREP). Remarks.
Examples: CIG AOB 6 AND VSBY AOB 2S-F. CONDS CONTG BYD 1400Z AND SPRDG OVR OH WRN PA AND NY.
CIGS/VSBYS BLO 10/3 XPCD BTWN 1600 AND 2000Z IN RAIN AND FOG. CONDS IPVG FM SW AFT 1800Z.
8.2.7 Extensive Mountain Obscuration. When conditions over significant portions of mountainous geographical regions are such that pilots in flight should not expect to maintain VFR or visual contact with mountains or mountain ridges near their route of flight, the area affected by such conditions shall be detailed in the IFR AND MTN OBSCN AIRMET bulletin.
Format: MTNS/MTN RDGS, (OCNLY) OBSCD (ABV/BLO hhh), (BY phenomenon)/RPRTD BY (PIREP). Remarks.
Examples: MTNS OCNLY OBSCD ABV 70 BY RAIN SHWRS. CONDS CONTG BYD 0200Z.
MTN RDGS OBSCD BY CLDS AND DRZL. CONDS IPVG AFT 0800Z.
8.2.8 Relationship of AIRMETs to Tropical Storm and/or Hurricane Advisories. Weather conditions meeting AIRMET criteria, which result from tropical storms or hurricanes shall be referenced in the "cause" phrase of the AIRMET as fol 1 owq
DUE TO TRPCL STM/HURCN name. SEE LAmanual ADVISORY.
8.2.9 Examples. The following are complete examples of AIRMET bulletins including NWS, WMO, and FAA headers.
ZCZC MKCWA3S ALL 300745
WAUS1 KCHI 300745
CHIS WA 300745
AIRMET SIERRA FOR IFR VALID UNTIL 301400
AIRMET IFRIA MO
FROM FOD TO CID TO COU TO MKC TO FOD
CIG BLO 10 AND VSBY BLO 3S-. CONDS CONTG BYD 1400Z AND SPRDG OVR
ERN IA ERN MO AND IL.
IFR OTLK VALID 1400-20001A MN WI IL
CIG BLO 10 A-ND VSBY BLO 3S- SPRDG INTO NERN IA SRN MN SWRN WI AND
NWRN IL BTWN 1600Z AND 2000Z CONTG BYD 2000Z.
....
NNNN
ZCZC MKCWA1S ALL 191345
WAUS1 KBOS 191345
BOSS WA 191345
AIRMET SIERRA FOR MTN OBSCN VALID UNTIL 192000
AIRMET MTN OBSCN...ME NH VT NY PA WV VA MD MA FROM CAR TO CON TO LYH TO TRI TO HNN TO SLK TO CAR MTNS OBSCD BY CLDS/PCPN. CONDS CONTG BYD 2000Z AND ENDG SRN HALF AFT 00Z.
NNNN
ZCZC MKCWA1Z ALL 192000
WAUS1 KBOS 192000
BOSZ WA 192000
AIRMET ZULU FOR ICG AND FRZLVL VALID UNTIL 200200
AIRMET ICG...NH VT LO NY PA LE OH WV VA DC MD DE NJ CT RI MA AND
ADJ CSTL WTRS
FROM YSC TO ACK TO ACY TO TRI TO FDY TO YYZ TO YSC
OCNL MDT RIME OR MXD ICGICIP FROM FRZLVL TO 180. CONDS CONTG BYD
0200Z.
ME
OCNL LGT RIME ICGIC FRZLVL TO 200 CONTG BYD 0200Z.
FRZLVL...100-120 THRUT.
OTLK VALID 0200-0800...ME
OCNL MDT RIME FRZLVL TO 180 SPRDG INTO SWRN ME BY 0400Z AND CONTG THRUT NERN ME BY 0800Z CONTG BYD 0800Z.
NNNN
ZCZC MKCWA1T ALL 191345
WAUS1 KBOS 191345
BOST WA 191345
AIRMET TANGO FOR TURBCSTG SFC WINDS AND LLWS VALID UNTIL 192000
...SEE SIGMET PAPA SERIES FOR SVR TURBC AREA...
AIRMET TURBCME NH
FROM CAR TO YSJ TO CON TO YSC TO CAR
OCNL MDT TURBC BLO 80 WITH STG UDDFS VCNTY MTNS DUE TO MDT NWLY
WIND. CONDS CONTG BYD 2000Z.
LLWS POTENTIAL ME AND NH ASSOCD WITH CDFNT.
OTLK VALID 2000-0200Z
AREA 1ME NH
OCNL MDT TURBC BLO 80 DMSHG BTWN 0000Z AND 0200Z OVR ENTR AREA.
AREA 2LO NY PA WV MD
OCNL MDT TURBC BLO 60 DVLPG OVR WRN LO WRN NY WRN PA WV AND WRN MD
PNHNDL BTWN 2000-0200Z CONTG/SPRDG EWD AFT 0200Z.
NNNN
ZCZC MKCWA3T ALL 190745
WAUS1 KCHI 190745
CHIT WA 190745
AIRMET TANGO FOR TURBC VALID UNTIL 191400
AIRMET TURBCND SD NE KS MN IA
FROM INL TO DLH TO OSW TO 40W LBL TO GLD TO BFF TO ISN TO INL
OCNL MDT TURBC BLO 60 DUE TO STG AND GUSTY LOW LVL WINDS. CONDS
ENDG AFT 1400
....
NNNN
ZCZC MKCWA4Z ALL 190145 WAUS1 KDFW 190145 DFWZ WA 190145 AIRMET ZULU FOR ICG AND FRZLVL VALID UNTIL 190800
NO SGFNT ICG XPCD.
FRZLVL...90-120 E OF DYR-MSL-ATL LN SLPG TO 120-140 OVR RMNDR.
....
NNNN
ZCZC MKCWA4T ALL 191345
WAUS1 KDFW 191345
DFWT WA 191345
AIRMET TANGO FOR TURBC...STG SFC WNDS AND LLWS VALID UNTIL 192000
AIRMET TUR8COK TX KS
FROM OSW TO LRD TO PEQ TO 40W LBL TO OSW
OCNL MDT TURBC BLO 60 DUE TO STG AND GUSTY LOW LVL WINDS.
CONDS CONTG BYD 2000Z.
AIRMET STG SFC WINDS...TX
FROM CDS TO DFW TO SAT TO MAF TO CDS
AFT 18Z...SUSTAINED SFC WINDS GTR THAN 30KT XPCD. CONDS CONTG BYD 2000Z.
LLWS BLO 20 AGL DUE TO STG WINDS DMSHG BY 16-18Z.
OTLK VALID 2000-0200Z...OK TX AR MDT TURBC BLO 60 CONTG OVR OK/TX AND SPRDG INTO AR BY 2200-0200Z CONTG ENTR AREA BYD 0200Z.
....
NNNN
ZCZC MKCWA5S ALL 191345
WAUS1 KSLC 191345
SLCS WA 191345
AIRMET SIERRA FOR IFR AND MTN OBSCN VALID UNTIL 192000
AIRMET IFRWY CO NE
FROM 70ENE GCC TO GLD TO FMN TO 60N JAC TO 70ENE GCC
OCNL CIGS BLO 10 AND OR VSBYS BLO 3 IN PCPN AND FOG. CONDS CONTG
BYD 2000Z AND GRDLY DMSHG.
AIRMET MTN OBSCN...ID MT WY UT CO FROM YXC TO YXH TO AKO TO TBE TO FMN TO LXT TO YXC MTNS OCNL OBSCD IN CLDS/PCPN. CONDS CONTG BYD 2000Z.
OTLK VALID 2000-0200ZMTN OBSCN MT WY CO
CONDS CONTG BYD 0200Z IN WY/CO BUT ENDING IN MT BTWN 2200-0200Z.
....
NNNN
9. Preliminary Notification of Forthcoming Severe Weather Watches. An alert weather watch (AWW) message for all average weather watches about to be issued shall be transmitted to the FAA's Weather Message Switching Center prior to the release of a watch.
Each AWW issued shall include the fixed formatted information as shown in the example. In addition, all distances shall be in statute miles; times in UTC; and half-widths of the area shall always be given.
Example: MKCSAW7
WWUS40 KMKC 150220
MKC AWW 150220
WW 107 SEVERE THUNDERSTORM OK 150220Z-150620Z.
AXIS 70 STATUTE MILES EITHER SIDE OF LINE35 WSW OF CSM/CLINTON
OK/-20 E OF BVO/BARTLESVILLE OK/.
AVIATION COORDS60 NM EITHER SIDE OF LINE52NNE CDS-32SW OSW.
HAIL SURFACE AND ALOFT3 INCHES. SURFACE WIND GUSTS80 KNOTS.
TOPS650. MEAN WIND VECTOR25030. REPLACES WW 106.
9.1 Cancellation Message. If an AWW must be canceled during its existing valid period, the following information as shown in the example shall be used to cancel the AWW.
Example:
MKCSAW7
WWUS40 KMKC 150430
MKC AWW 150430
WW 107 SEVERE THUNDERSTORM CANCELED
10. In-flight Advisory Message Headers in Various Communications Systems. Listed below are the communications message headers used for AIRMETs, nonconvective SIGMETs, and Convective SIGMETs in the FAA communications system, the NWS AFOS system, and any systems using the WMO communications standards. In each system the header includes the message type and an identifier for the originating office (or, for the contiguous United States, the area covered). The NWS and FAA headers also include the alphabetic designator.
|
FAA
|
WMO
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AFOS
|
|
AIRMETs
|
|
|
|
BOSS, T, and Z WA
|
WAUS1 KBOS
|
MKCWA1S, T, and Z
|
|
MIAS, T, and Z WA
|
WAUS1 KMIA
|
MKCWA2S, T, and Z
|
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CHIS, T, and Z WA
|
WAUS1 KCHI
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MKCWA3S, T, and Z
|
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DFWS, T, and Z WA
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WAUS1 KDFW
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MKCWA4S, T, and Z
|
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SLCS, T, and Z WA
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WAUS1 KSLC
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MKCWA5S, T, and Z
|
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SFOS, T, and Z WA
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WAUS1 KSFO
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MKCWA6S, T, and Z
|
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JNUS, T, and Z WA
|
WAAK1 PAJN
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NMCWA7S, T, and Z
|
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ANCS, T, and Z WA
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WAAK1 PANC
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NMCWA8S, T, and Z
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FAIS, T, and Z WA
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WAAK1 PAFA
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NMCWA9S, T, and Z
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HNLS, T, and Z WA
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WAHW1 PHNL
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NMCWAOS, T, and Z
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SIGMETs
|
|
|
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BOSi WS
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WSUS1 KBOS
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MKCWSli
|
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MIAi WS
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WSUS1KMIA
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MKCWS2i
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CHIi WS
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WSUS1 KCHI
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MKCWS3i
|
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DFWi WS
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WSUS1 XDFW
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MKCWS4i
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SLCi WS
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WSUS1 KSLC
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MKCWS5i
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SFOi WS
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WSUS1 RSFO
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MKCWS6i
|
Where "i" is N through Y excluding S AND T.
Convective SIGMETs
|
MKCg WST
|
WSUS4x KMKC
|
MKCWSTg
|
Where "g" is E, C, or W, and "x" is 0, 1, or 2, each indicating the geographical section of the country covered.
11. Procedures for Backup of the NAWAU. This section details the procedures to be followed in the event that NAWAU is unable to produce or disseminate its aviation In-flight Advisories (AIRMETs and SIGMETs). Since it is anticipated that such an occurrence would also result in the loss of FAs, the procedures for the backup of both types of products are detailed here as well as WSOM Chapter D-20. Backup procedures for Alaska and Hawaii are detailed in Regional Operation Manual Letters and Station Duty Manuals.
11.1 Policy. The significant or total loss of product-generating or -disseminating capability at the NAWAU shall result in the transfer of In-flight Advisory responsibility to six designated WSFOs (Washington, Miami, Chicago, Fort Worth, Salt Lake City, and San Francisco). The transfer of any additional responsibilities to these offices is infeasible. Therefore, the FA shall be suspended in the event that the NAWAU is incapacitated.
11.2.1 Test Requirements. Backup tests shall be performed quarterly in the contiguous states and twice yearly in Alaska and Hawaii. These tests shall be performed in accordance with WSOM Chapters J-03 and/or J-07.
a. For planned or anticipated outages (advance knowledge):
(1) NAWAU shall advise the six designated WSFOs; Topeka, Kansas; and the Central Flow Weather Service Unit (CFWSU) of the anticipated time and duration of the outage. Notification shall be made via telephone asRIEB (D-22)
early as possible to allow for any required staffing changes and an orderly handoff of advisory responsibility.
(2) The CFWSU shall immediately advise the CWSUs of the outage information. During the hours when there is no CWSU coverage, the CFWSU shall inform the facility shift chief and discuss the option of staffing the CWSU in order to provide CWA coverage.
(3) NAWAU shall:
- amend each FA to append the message, ."BACKUP PROCEDURES IN EFFECT BEGINNING ddtttt...SEE AIRMET SiSIGMETS" to the end of each HAZARDS section;
- append the message, "BACKUP PROCEDURES IN EFFECT BEGINNING ddtttt.,.NO FA AVBL TIL (ddtttt OR FTHR NOTICE)" to the end of each SYNOPSIS AND VFR CLDS/WX section; and
- append the message, "BACKUP PROCEDURES IN EFFECT BEGINNING ddtttt to the end of each of what will be its last scheduled Convective SIGMET (E, C, and w) and AIRMET bulletins prior to the outage, and to any nonconvective SIGMETs issued within 4 hours of the start time of the outage.
b. For unplanned outages:
(1) NAWAU shall immediately contact the six designated WSFOs and handoff advisory responsibility. These offices will be advised of the anticipated duration of the outage, if known. WSFO Topeka and the CFWSU shall then be contacted. Notification shall be made by telephone or whatever alternative is available.
(2) The CFWSU shall pass the outage notification along to the CWSUs/Air Route Traffic Control Centers (ARTCC). During the hours when there is no CWSU coverage, the facility shift chiefs shall be informed of the anticipated outage and the advisability of staffing the CWSU in order to provide CWA coverage will be discussed. If the outage occurs during periods when the CFWSU may not be in operation, the designated WSFOs shall contact the ARTCC(s) located with their assigned advisory area and convey the information as outlined above.
(3) WSFO Topeka shall:
- amend each FA to append the message, "BACKUP PROCEDURES IN EFFECT BEGINNING ddtttt...SEE AIRMETS/SIGMETS" to the end of each HAZARDS section;
append the message, "BACKUP PROCEDURES IN EFFECT BEGINNING ddtttt...NO FA AVBL TIL (ddtttt OR FTHR NOTICE)" to the end of each SYNOPSIS AND VFR CLDS/WX section: and
amend each current Convective SIGMET (E, C, and W) and AIRMET bulletin and any nonconvective SIGMET(s) to append the message, "BACKUP PROCEDURES IN EFFECT BEGINNING ddtttt" after an outage has been determined.
This message shall be issued using the NAWAU FA headers and sent via both the Weather Message Switching Center (WMSC) and the AFOS system.
(4) WSFO Topeka shall issue the message, "BACKUP PROCEDURES IN EFFECT BEGINNING ddtttt...SEE SIGMETS FOR CONVECTIVE ACTIVITY" in place of the scheduled Convective SIGMETs. These messages shall be issued on an hourly basis between H+50 and H+54, using the NAWAU headers and transmitted via the WMSC and AFOS systems. They will continue until WSFO Topeka is notified that the NAWAU is back in operation.
11.2.3 Operations. Upon notification of an anticipated outage or of the handoff of advisory responsibility, the designated WSFOs shall assign a position to begin a MET Watch of their in-flight advisory areas. Additional preliminary duties for this position include:
- review backup procedures,
- review In-flight Advisory criteria and procedures,
- ensure that the WSFO data base contains sufficient information to support the additional forecaster requirements,
- expand the data base if necessary, and
- coordinate with adjoining offices where weather which meets or approaches advisory criteria is affecting more than one FA region or is approaching region boundaries.
Upon handoff of advisory responsibility, any existing Convective SIGMETs shall continue until expiration. When the expiration time is reached, no additional Convective SIGMETs will be issued. Except as noted, forecasters shall use the criteria and procedures prescribed for international SIGMETs to issue 4 hourly SIGMETs for "active thunderstorms' in lieu of hourly Convective SIGMETs. For details, see excerpt from WSOM Chapter D-38 below.
WSOM Chapter D-38 excerpts:
5. Elements of SIGMET Information. SIGMET information shall include the occurrence and/or expected occurrence of one or more of the following:
a. at subsonic cruising levels:
- active thunderstorms
- tropical cyclone (Not done for domestic backup)
- severe line squall
- heavy hail (i.e., Large, greater than or equal to 3/4")
- severe turbulence
- severe icing
- marked mountain waves (Not done for domestic backup)
- widespread sandstorm/duststorm
- volcanic ash cloud;
b. at transonic levels and supersonic cruising levels: - moderate or severe turbulence - cumulonimbus clouds - hail - volcanic ash cloud.
Note: The terms "subsonic cruising levels," "transonic levels," and "supersonic cruising levels" and the associated criteria are taken from ICAO Annex 3, chapter 7, and are acknowledged to be ambiguous, often representing considerable overlap. For example, subsonic aircraft may operate at FL530 or higher and aircraft capable of flying faster than the speed of sound may begin transonic operations (i.e., transitioning from subsonic to supersonic speeds) at FL250 or even lower. The significance of the distinction between meteorological effects as given by paragraphs 5a and 5b, above, is that aircraft operating at supersonic speeds are vulnerable to damage from meteorological conditions generally considered not to be hazardous to aircraft operating at speeds below the speed of sound. Supersonic cruising levels are generally considered to be at or above FL530 and subsonic cruising levels are generally considered to be at or below FL530.
5.1 "Active Thunderstorms" Defined. The requirement to issue SIGMET information regarding active thunderstorms refers to the occurrence or expected occurrence of an area (3,000 square nautical miles or- more) of widespread cumulonimbus clouds or cumulonimbus along a line with little or no space between individual clouds, or to cumulonimbus embedded in cloud layers or concealed by haze. It does not refer to isolated or scattered cumulonimbus not embedded in cloud layers or concealed by haze. From a different perspective, cumulonimbus clouds that can be avoided by visual observation from the flight deck are not considered to be "active thunderstorms" in the sense of this definition.
5.2 (Not excerpted here)
5.3 Unnecessary Descriptive Material. SIGMET messages should not contain unnecessary descriptive material. For example, messages concerning an area of active thunderstorms, a tropical cyclone, or a severe line squall should not include references to associated turbulence, icing, or hail, unless the associated phenomena are considered to warrant special attention. In tropical areas, during periods when thunderstorm activity is a frequent occurrence, SIGMET messages relating to that phenomenon should only be issued with respect to active thunderstorms as defined in section 5.1. above.
End of Excerpts.
Examples: The following are complete examples of SIGMETs for active thunderstorms.
DFWR UWS 142200
SIGMET ROMEO 1 VALID UNTIL 150200
TX LA
FROM LFK TO AEX TO LCH TO PSX TO LFK
ISOLD TSTMS EMBDD IN HAZE MOVG FM 2415. TOPS TO 390. CONDS ENDG BY 0200Z
CHIY WS 202000
SIGMET YANKEE 2 VALID UNTIL 210000
WI IA IL MO
FROM LSE TO MKE TO ARG TO SGF TO LSE
LN TSTMS 20MI WIDE MOVG FROM 2925. TOPS TO 450. CONDS CONTG BYD 0000Z
In addition to replacing Convective SIGMETs with SIGMETs for "active thunderstorms," the designated backup WSFOs shall monitor conditions during that period and use the information in sections 7 and 8 of this chapter to determine whether any nonconvective SIGMET or AIRMET threshold criteria have been met. If thunderstorms or other conditions meet applicable criteria, appropriate products shall be issued using the relevant NAWAU headers listed in section 10 of this chapter.
If the outage occurs just prior to the scheduled issuance time of the NAWAU product, the backup product should be issued as soon as the forecaster determines that sufficient information is available at the backup office to support an adequate advisory.
Upon handoff of advisory responsibility, if no advisory criteria are met, the designated offices shall maintain an advisory meteorological watch and issue advisories as per this chapter for nonconvective criteria and for thunderstorms.
Resumption of the FA and the return of advisory responsibility to the NAWAU shall be initiated by the NAWAU after adequate operational capability and data availability has been ensured. At the time of handoff, a new FA (with the "VALID UNTIL" time of the FA regularly scheduled for issuance prior to the time operations resumed) shall be issued by the NAWAU. Exceptions to this are: no new FA issuance is required if the outage and resumption of service occur within the valid period of a single FA or if the next regularly scheduled FA issuance is within 2 hours of resumption of service. Also at the time of handoff, messages canceling any existing SIGMETs for thunderstorms shall be transmitted by the issuing office(s). Existing nonconvective advisories shall continue to their expiration times while being monitored by the NAWAU.
11.2.4 Communications. All offices with an issuance responsibility during NAWAU backup shall add the required AFOS product keys to their data bases. In order for AFOS and NWS Telecommunications GATEWAY distribution to occur, the "national bits" of each key must be set. Once this is done, the NAWAU products, which are not normally transmitted via the telecommunications GATEWAY, can be backed up by products issued under designated node identifiers which are programmed for distribution via GATEWAY. Since these products will be transmitted as "national" products, other AFOS offices will continue to store them under their own local nodes.
12. Retention. WSOM Chapter D-90 contains all necessary details on the NWS service record retention program and shall be followed with regard to retention of In-flight Advisories.
WSOM
91-7 5-22-91