Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) 6 PRODUCTS FOR AVIATION HAZARDS
6.1 Significant Meteorological Information (SIGMET) A SIGMET is a concise description of the occurrence or expected occurrence of specified en route weather phenomena which may affect the safety of aircraft operations. SIGMETs are intended for dissemination to all pilots in flight to enhance safety. SIGMETs are issued by the responsible MWO as soon as practical to give notice to operators and aircrews of potentially hazardous en-route conditions.
• SIGMETs are available on the Aviation Digital Data Service (ADDS) web site at:
http://adds.aviationweather.noaa.gov/airmet/
o Alaska SIGMETs are also available on the Alaska Aviation Weather Unit (AAWU) web site at: http://aawu.arh.noaa.gov/
o Hawaii SIGMETs are also available on the NWS WFO Honolulu web site at:
http://www.prh.noaa.gov/hnl/pages/aviation.php
6.1.1 SIGMET Issuance SIGMETs are issued from Meteorological Watch Offices (MWO). The U.S. has three MWOs:
the Aviation Weather Center (AWC), the Alaska Aviation Weather Unit (AAWU), and the Weather Forecast Office (WFO) in Honolulu. Their areas of responsibility are as follows:
• The AWC:
o Twenty (20) domestic Air Route Traffic Control Center (ARTCC) Flight Information Regions (FIRs) covering the conterminous U.S. (CONUS) and adjacent coastal waters (Figure 6-1).
o The New York, Houston, Miami, and San Juan Oceanic FIRs (Figure 6-2).
o The Oakland Oceanic FIR north of 30 north latitude, and the portion east of 140 west longitude which is between the equator and 30 north latitude (Figure 6-3).
• The AAWU is responsible for the Anchorage Continental FIR and Anchorage Oceanic FIR (Figure 6-3).
• WFO Honolulu is responsible for the Oakland Oceanic FIR south of 30 north latitude and between 140 west and 130 east longitude (Figure 6-3).
AC 00-45F, CHG 2 Section 6: Products for Aviation Hazards Page 6-1
Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) San Francisco Chicago Boston Salt Lake City Dallas/Fort Worth Miami Figure 6-1. AWC SIGMET Areas of Responsibility - Conterminous U.S.
NEW YORK OCEANIC FIR
• 130
HOUSTON MIAMI
OCEANIC OCEANIC Q MIAMI FIR FIR OCEANIÇ SER SAN JUAN ı20 → FIR
- 90 - 80 <øБ0 -50 -40 Figure 6-2. AWC SIGMET Areas of Responsibility - Atlantic Basin AC 00-45F, CHG 2 Section 6: Products for Aviation Hazards Page 6-2
Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009)
Figure 6-3. SIGMET Areas of Responsibility – Pacific Basin
6.1.1.1 SIGMET Identification When a SIGMET is issued, it is assigned a unique series identifier:
• AWC for CONUS o NOVEMBER through YANKEE, excluding SIERRA and TANGO
• AWC for Oakland Oceanic FIR o ALFA through HOTEL
• Honolulu MWO for Oakland Oceanic FIR o NOVEMBER through ZULU
• AAWU for Anchorage FIR o INDIA through MIKE AC 00-45F, CHG 2 Section 6: Products for Aviation Hazards Page 6-3
Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009)
A number is assigned sequentially with each issuance until the phenomenon ends. At 0000 UTC each day, all continuing SIGMETs are renumbered to one (1) regardless of a continuation of the phenomena. (e.g., YANKEE 1, YANKEE 2, YANKEE 3, etc.)
6.1.2 SIGMET Standardization SIGMETs follow these standards:
• All heights or altitudes are referenced to above mean sea level (AMSL), unless otherwise noted, and annotated using the height in hundreds of feet, consisting of three digits (e.g., 040). For heights at or above 18,000 feet, the level is preceded by FL to represent flight levels (e.g., FL180).
• References to latitude and longitude are in whole degrees and minutes following the model: Nnn[nn] or Snn[nn], Wnnn[nn] or Ennn[nn] with a space between latitude and longitude and a hyphen between successive points. Example: N3106 W07118 – N3011 W7209
• Messages are prepared in abbreviated plain language using contractions from the Federal Aviation Administration (FAA) Order 7340.1Z for domestic products and International Civil Aviation Organization (ICAO) document 8400 for international products issued for Oceanic FIRs. A limited number of non-abbreviated words, geographical names and numerical values of a self-explanatory nature may also be used.
• Weather and obstructions to visibility are described using the weather abbreviations for surface weather observations (METAR/SPECI). See the Federal Meteorological Handbook (FMH) No. 1 – Surface Observations or Section 3.1 of this document.
Note: Refer to Appendix A for definitions of common terms used in SIGMETs.
6.1.3 SIGMET (Non-Convective) – Conterminous U.S.
6.1.3.1 SIGMET (Non-Convective) Issuance Criteria – Contiguous U.S.
A SIGMET may be issued in the Contiguous U.S. when any of the following conditions are affecting or, in the judgment of the forecaster, are expected to affect an area of at least 3,000 square miles or an area judged to have a significant impact on the safety of aircraft operations.
• Severe or greater Turbulence (SEV TURB)
• Severe Icing (SEV ICE)
• Widespread Duststorm (WDSPR DS)
• Widespread Sandstorm (WDSPR SS)
• Volcanic Ash (VA)
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Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009)
6.1.3.2 SIGMET (Non-Convective) Issuance Time and Valid Period – Conterminous U.S.
A SIGMET is an unscheduled product issued any time conditions reaching SIGMET criteria are occurring or expected to occur within a 4-hour period. A SIGMET can have a valid period up to, but not exceeding, four (4) hours. SIGMETs for continuing phenomena will be reissued at least every 4 hours as long as SIGMET conditions continue to occur in the area for responsibility.
6.1.3.3 SIGMET (Non-Convective) Format – Conterminous U.S.
The content and order of elements in the SIGMET are as follows:
• series name and number
• valid beginning and ending time (UTC)
• list of states affected by the phenomena
• location of phenomena delineated by high-altitude VOR coordinates covering the affected area during the SIGMET valid time
• phenomena description (e.g., SEV ICE)
• vertical extent (base and top), if appropriate
• movement, if appropriate
• intensity change (INTSF – intensifying, WKN – weakening, NC – no change)
• Indication that the whether the condition will continue during the 4 hours beyond the valid time of the SIGMET AC 00-45F, CHG 2 Section 6: Products for Aviation Hazards Page 6-5
Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009)
Figure 6-4. SIGMET for the Conterminous U.S. Decoding Example
Table 6-1. Decoding a SIGMET (Non-Convective) for the Conterminous U.S.
Line Content Description 1 SFO SIGMET area identifier R SIGMET series WS Product identifier 100130 Issuance date/time UTC 2 SIGMET Product type ROMEO SIGMET series name 1 Series issuance number VALID UNTIL 100530 Ending valid date/time UTC 3 OR WA Phenomenon location (states) 4 FROM SEA TO PDT TO EUG TO SEA Phenomenon location (highaltitude VOR coordinates) 5 OCNL MOGR CAT BTN FL280 AND FL350 EXP DUE TO JTSTR. CONDS BGNG AFT 0200Z CONTG BYD 0530Z AND SPRDG OVR CNTRL ID BY 0400Z.
Phenomenon description
The SIGMET in Figure 6-4 is decoded as the following:
(Line 1) SIGMET ROMEO series issued for the San Francisco Area at 0130 UTC on the 10th day of the month.
(Line 2) This is the first issuance of the SIGMET ROMEO series and is valid until the 10th day of the month at 0530 UTC.
(Line 3) The affected states within the SFO area are Oregon and Washington.
(Line 4) From Seattle, WA; to Pendleton, OR; to Eugene, OR; to Seattle, WA;
AC 00-45F, CHG 2 Section 6: Products for Aviation Hazards Page 6-6
Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009)
(Line 5) Occasional moderate or greater clear air turbulence between Flight Level 280 and Flight Level 350, expected due to jet stream. Conditions beginning after 0200Z continuing beyond 0530Z and spreading over central Idaho by 0400Z.
6.1.3.4 SIGMET (Non-Convective) Cancellations – Conterminous U.S.
A CONUS non-convective SIGMET is canceled when the phenomena is no longer occurring or no longer expected to occur or has moved out of the area of responsibility.
6.1.3.5 SIGMET (Non-Convective) Amendments – Conterminous U.S.
Amendments to CONUS non-convective SIGMETs are NOT issued. Instead, a new SIGMET is issued using the next series number.
6.1.3.6 SIGMET (Non-Convective) Corrections – Conterminous U.S.
Corrections to CONUS non-convective SIGMETs are issued as necessary. The corrected SIGMET is identified by a “COR” located at the end of the first line after the issuance UTC date/time.
6.1.3.7 SIGMET (Non-Convective) Example – Conterminous U.S.
WSUS01 KKCI 050600 WS1R BOSR WS 050600 SIGMET ROMEO 2 VALID UNTIL 051000
ME NH VT
FROM CAR TO YSJ TO CON TO MPV TO CAR SEV TURB OBS AND FCST BLW 080. CONDS CONTG BYD 1000Z.
SIGMET (WSUS01) issued by the Meteorological Watch Office (WMO) (Aviation Weather Center) in Kansas City, Missouri (KKCI) on the 5th day of the month at 0600 UTC. The National Weather Service AWIPS communication header for this product is WSR1. SIGMET issued for the Boston Area Forecast region on the 5th day of the month at 0600 UTC. This is the second (2nd) issuance of SIGMET series Romeo and is valid until the 5th day of the month at 1000 UTC. The affected states are Maine (ME), New Hampshire (NH) and Vermont (VT). Within an area bounded from Caribou, Maine (CAR) to St. Johns, New Brunswick (YSJ); to Concord, New Hampshire (CON); to Montpelier, Vermont (MPV); to Caribou, Maine (CAR). Severe turbulence observed and forecast below 8,000 feet. Conditions continuing beyond 1000 UTC.
6.1.4 Convective SIGMET Convective SIGMETs are issued for the conterminous U.S. (CONUS) instead of SIGMETs for thunderstorms. Any Convective SIGMET implies severe or greater turbulence, severe icing, and low level wind shear.
6.1.4.1 Convective SIGMET - Routine Issuance Criteria A Convective SIGMET will be issued when any of the following conditions are occurring or, in the judgment of the forecaster, are expected to occur:
• A line of thunderstorms at least 60 miles long with thunderstorms affecting at least 40 percent of its length.
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Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009)
• An area of active thunderstorms affecting at least 3,000 square miles covering at least 40 percent of the area concerned and exhibiting a very strong radar reflectivity intensity or a significant satellite or lightning signature.
• Embedded or severe thunderstorm(s) expected to occur for more than 30 minutes during the valid period regardless of the size of the area.
6.1.4.2 Convective SIGMET - Special Issuance Criteria A special Convective SIGMET may be issued when any of the following criteria are occurring or, in the judgment of the forecaster, are expected to occur for more than 30 minutes of the valid period.
• Tornado, hail greater than or equal to ¾ inch (at the surface), or wind gusts greater than or equal to 50 knots (at the surface) are reported.
• Indications of rapidly changing conditions, if in the forecaster’s judgment, they are not sufficiently described in existing Convective SIGMETs.
• Special issuance is not required for a valid Convective SIGMET.
6.1.4.3 Convective SIGMET Issuance Time and Valid Period Convective SIGMET bulletins for the eastern, central and western regions of the conterminous U.S. (Figure 6-5) are issued on a scheduled basis, hourly at 55 minutes past the hour. Each bulletin contains all valid Convective SIGMETs within the region. Convective SIGMETs are valid for two (2) hours or until superseded by the next hourly issuance. A Convective SIGMET bulletin must be transmitted each hour for each region. When conditions do not meet or are not expected to meet Convective SIGMET criteria within a region at the scheduled time of issuance a “CONVECTIVE SIGMET...NONE” message is transmitted.
Figure 6-5. AWC Convective SIGMET Areas of Responsibility
AC 00-45F, CHG 2 Section 6: Products for Aviation Hazards Page 6-8
Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009)
6.1.4.4 Convective SIGMET Format Each Convective SIGMET bulletin includes one or more individually numbered Convective SIGMETs for the region. The content and order of each bulletin is as follows:
• CONVECTIVE SIGMET series number and region letter (E, W or C)
• Valid ending time (UTC)
• list of states affected by the phenomena
• location of phenomena delineated by high-altitude VOR coordinates covering the affected area during the SIGMET valid time
• phenomena description (e.g., AREA SEV EMBD TS)
• movement (e.g., MOV FROM 26030KT)
• cloud top (e.g., TOPS ABV FL450)
• remarks (e.g., TORNADOES...HAIL TO 2.5 IN...WIND GUSTS TO 70KT POSS)
Note: Tropical Cyclone information will be added to remarks section of the CONUS Convective SIGMETs when appropriate.
Note: Refer to Appendix A for definitions of common terms used in Convective SIGMETs.
AC 00-45F, CHG 2 Section 6: Products for Aviation Hazards Page 6-9
Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009)
Figure 6-6. Convective SIGMET Decoding Example
Table 6-2. Decoding a Convective SIGMET Line Content Description 1 MKC Issuing Office (AWC) C Region (East, Central or West) WST Product Identifier 221855 Issuance date/time (DDHHMM) 2 CONVECTIVE SIGMET Product type 20 Issuance number C Region (East, Central or West) 3 VALID UNTIL 2055Z Valid ending time (UTC) 4 ND SD States/areas affected 5 FROM 90W MOT-GFK-ABR-90W MOT Phenomenon location (high altitude VOR coordinates) 6 INTSFYG AREA SEV TS MOVG FROM 24045KT. TOPS ABV FL450. WIND GUSTS TO 60KTS RPRTD.
TORNADOES…HAIL TO 2 IN… WIND GUSTS TO 65KTS POSS ND PTN Phenomenon description, movement, cloud top, remarks
The Convective SIGMET in Figure 6-6 is decoded as the following:
(Line 1) Convective SIGMET issued for the central portion of the United States on the 22nd at 1855Z.
(Line 2) This is the 20th Convective SIGMET issued on the 22nd for the central United States as indicated by “20C.”
(Line 3) Valid until 2055Z
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Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) (Line 4) The affected states are North and South Dakota.
(Line 5) From 90 nautical miles west of Minot, ND; to Grand Forks, ND; to Aberdeen, SD; to 90 nautical miles west of Minot, ND.
(Line 6) An intensifying area of severe thunderstorms moving from 240 degrees at 45 knots (to the northeast). Thunderstorm tops above Flight Level 450. Wind gusts to 60 knots reported.
Tornadoes, hail to 2 inches in diameter, and wind gusts to 65 knots possible in the North Dakota portion.
6.1.4.5 Convective SIGMET Outlook Each Convective SIGMET bulletin includes a 2- to 6-hour outlook at the end of the bulletin. The content and order of each bulletin is as follows:
• Beginning and ending valid times
• Location of expected Convective SIGMET issuances delineated by high-altitude VOR coordinates for the outlook valid time.
• Discussion of forecast
6.1.4.6 Convective SIGMET Cancellations Convective SIGMETs are not cancelled but are superseded by the next Convective SIGMET in the series.
6.1.4.7 Convective SIGMET Amendments Amended Convective SIGMETs are NOT issued. Instead, a new Convective SIGMET is issued for that region.
6.1.4.8 Convective SIGMET Corrections Corrections to Convective SIGMETs are issued as necessary. The corrected Convective SIGMET is identified by a “COR” located at the end of the first line after the issuance UTC date/time.
6.1.4.9 Convective SIGMET Bulletin Examples
WSUS33 KKCI 091855 SIGW CONVECTIVE SIGMET...NONE .
OUTLOOK VALID 092055-100055 TS ARE NOT EXPD.
Convective SIGMET bulletin for the western region of the conterminous U.S.(WSUS33) issued by the Meteorological Watch Office (WMO) (Aviation Weather Center) in Kansas City, Missouri (KKCI) on the 9th day of the month at 1855 UTC. The National Weather Service AWIPS communication header for this product is SIGW.
No Convective SIGMETs are in effect.
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Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) The outlook portion of the Convective SIGMET bulletin is valid from the 9th day of the month at 2055 UTC to the 10th day of the month at 0055 UTC. Thunderstorms are not expected.
WSUS32 KKCI 091855 SIGC MKCC WST 091855 CONVECTIVE SIGMET 21C VALID UNTIL 2055Z AR OK FROM 20S RZC-40SSW FSM DMSHG LINE TS 25 NM WIDE MOV FROM 27025KT. TOPS TO FL320.
.
OUTLOOK VALID 092055-100055 FROM 40NE BUM-60SE SGF-50WSW LIT-40W GGG-60ENE ABI-ADM-50WNW BUM-40NE BUM WST ISSUANCES EXPD. REFER TO MOST RECENT ACUS01 KWNS FROM STORM PREDICTION CENTER FOR SYNOPSIS AND METEOROLOGICAL DETAILS.
Convective SIGMET bulletin for the central region of the conterminous U.S.(WSUS32) issued by the Meteorological Watch Office (Aviation Weather Center) in Kansas City, Missouri (KCCI) on the 9th day of the month at 1855 UTC. The National Weather Service AWIPS communication header for this product is SIGC.
Convective SIGMET (WST) for the central region of the conterminous U.S. issued by the Aviation Weather Center in Kansas City, Missouri (MKCC) on the 9th day of the month at 1855 UTC. Convective SIGMET 21C is the 21st Convective SIGMET issued for the central region of the conterminous US on the 9th day of the month. Valid until 2055 UTC. States affected are Arkansas (AR) and Oklahoma (OK). Bounded within an area from 20 nautical miles south of Razorback, Arkansas (RZC), to 40 nautical miles south-southwest of Fort Smith, Arkansas (FSM). A diminishing line of thunderstorms 25 nautical miles wide moving from 270 degrees (to the east) at 25 knots. Thunderstorms tops to FL320 (approximately 32,000 ft MSL).
The outlook portion of the Convective SIGMET bulletin is valid from the 9th day of the month at 2055 UTC to the 10th day of the month at 0055 UTC. Within an area bounded from 40 nautical miles northeast of Butler, Missouri (BUM), to 60 nautical miles southeast of Springfield, MO (SGF), to 50 nautical miles west-southwest of Little Rock, Arkansas (LIT), to 40 nautical miles west of Longview, Texas (GGG), to 60 nautical miles east-northeast of Abilene, Texas (ABI), to Ardmore, Oklahoma (ADM), to 50 nautical miles west-northwest of Butler, Missouri (BUM), to 40 nautical miles northeast of (BUM). Convective SIGMET issuances are expected. Refer to the most recent Day 1 Convective Outlook (ACUS01 KWNS) from the Storm Prediction Center (SPC) for a synopsis and meteorological details.
6.1.4.9.1 Convective SIGMET Bulletin – Tropical Cyclone Example
WSUS31 KKCI 211355 SIGE MKCE WST 211355 CONVECTIVE SIGMET 1E VALID UNTIL 1555Z
NC SC FL GA AND CSTL WTRS AC 00-45F, CHG 2 Section 6: Products for Aviation Hazards Page 6-12