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.
AC 00-45F, CHG 2 Section 6: Products for Aviation Hazards Page 6-7
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
AC 00-45F, CHG 2 Section 6: Products for Aviation Hazards Page 6-10
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.
AC 00-45F, CHG 2 Section 6: Products for Aviation Hazards Page 6-11
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
Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) FROM 30SSE CLT-160SE ILM-140ENE OMN-60E TLH-ABY-30SSE CLT AREA SEV EMBD TS MOV FROM 21015KT. TOPS ABV FL450.
TORNADOES...WIND GUSTS TO 60KT POSS.
TS ASSOCD WITH TROPICAL STORM ALBERTO.
.
OUTLOOK VALID 211555-211955 FROM 30E RDU-180SE ECG-140SSE ILM-180E PBI-40SE PBI-40S EYW-90SW EYW-70W SRQ-50N CTY-40N MCN-30NW SPA-30E RDU REF WW 475.
WST ISSUANCES EXPD. REFER TO MOST RECENT ACUS01 KWNS FROM STORM PREDICTION CENTER FOR SYNOPSIS AND METEOROLOGICAL DETAILS. REFER TO MOST RECENT WTNT21 KNHC FROM TROPICAL PREDICTION CENTER FOR DETAILS ON TROPICAL STORM ALBERTO.
Convective SIGMET bulletin for the eastern region of the conterminous U.S.(WSUS31) issued by the Meteorological Watch Office (Aviation Weather Center) in Kansas City, Missouri (KCCI) on the 21st day of the month at 1355 UTC. The National Weather Service AWIPS communication header for this product is SIGE.
Convective SIGMET (WST) for the eastern region of the conterminous U.S. issued by the Aviation Weather Center in Kansas City, Missouri (MKCE) on the 21st day of the month at 1355 UTC. Convective SIGMET 1E is the 1st Convective SIGMET issued for the eastern region of the conterminous US on the 21st day of the month. Valid until 1555 UTC. States affected are North Carolina (NC), South Carolina (SC), Florida (FL), Georgia (GA) and adjacent coastal waters.
Within an area bounded from 30 nautical miles south-southeast of Charlotte, North Carolina (CLT) to 160 nautical miles southeast of Wilmington, North Carolina (ILM) to 140 nautical miles east-northeast of Ormond Beach, Florida (OMN) to 60 nautical miles east of Tallahassee, Florida (TLH) to Albany, Georgia (ABY) to 30 nautical miles south-southeast of Charlotte, North Carolina (CLT). An area of severe embedded thunderstorms moving from 210 degrees at 15 knots. Cumulonimbus tops above flight level 450 (approximately 45,000 feet MSL) Tornadoes and surface wind gust to 60 knots are possible. The thunderstorms are associated with Tropical Storm Alberto.
The outlook portion of the Convective SIGMET bulletin is valid from the 21st day of the month at 1555 UTC to the 21st day of the month at 1955 UTC. Within an area bounded from 30 nautical miles east of Raleigh-Durham, North Carolina (RDU) to 180 nautical miles southeast of Elizabeth City, North Carolina (ECG) to 140 south-southeast of Wilmington, North Carolina (ILM) to 180 nautical miles east of (PBI) to 40 nautical miles southeast of West Palm Beach, Florida (PBI) to 40 nautical miles south of Key West, Florida (EYW) to 90 nautical miles southwest of Key West, Florida (EYW) to 70 nautical miles west of Sarasota, Florida (SRQ) to 50 nautical miles north of Cross City, Florida (CTY) to 40 nautical miles north of Macon, Georgia (MCN) to 30 nautical miles northwest of Sparta, Georgia (SPA) to 30 nautical miles east of Raleigh-Durham, North Carolina (RDU). Refer to Weather Watch Notification Message 475.
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. Refer to the most recent Tropical Cyclone Forecast/Advisory (WTNT21 KNHC) from the Tropical Prediction Center (TPC) for details on Tropical Storm Alberto.
6.1.5 SIGMET – Outside the Conterminous U.S. (O-CONUS)
AC 00-45F, CHG 2 Section 6: Products for Aviation Hazards Page 6-13
Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009)
6.1.5.1 SIGMET Issuance Criteria – Outside the Conterminous U.S. (O-CONUS) SIGMETs outside the Conterminous U.S. (O-CONUS SIGMETs) are issued when any of the following is occurring or expected to occur affecting an area greater than 3,000 square miles or, in the judgment of the forecaster, an area having the potential to have a significant effect on the safety of aircraft operations.
• Thunderstorm - of type below *
o Obscured (OBSC TS)
o Embedded (EMBD TS)
o Widespread (WDSPR TS)
o Squall line (SQL TS)
o Isolated severe (ISOL SEV TS)
• Severe Turbulence (SEV TURB)
• Severe Icing (SEV ICE)
o With Freezing rain (SEV ICE (FZRA)
• Widespread Duststorm (WDSPR DS)
• Widespread Sandstorm (WDSPR SS)
• Volcanic Ash (VA)
• Tropical Cyclone (TC)
NOTE: Obscured, embedded, or squall line thunderstorms do not have to reach 3,000 square miles criteria.
*Tornado (TDO), Funnel Cloud (FC), Waterspout (WTSPT), and Heavy Hail (HVY GR) may be used as a further description of the thunderstorm as necessary.
6.1.5.2 SIGMET Issuance Time and Valid Period – Outside the Conterminous U.S. (O- CONUS) 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 outside the conterminous U.S. (O-CONUS) can have a valid period up to, but not exceeding, four (4) hours, except for volcanic ash (VA) and tropical cyclone (TC) which can be valid up to six (6) hours. SIGMETs for continuing phenomena will be reissued at least every 4 (or 6) hours as long as SIGMET conditions continue to occur in the area for responsibility.
6.1.5.3 SIGMET Format – Outside the Conterminous U.S. (O-CONUS) O-CONUS SIGMETs contain the following information, related to the specific phenomena and in the order indicated:
AC 00-45F, CHG 2 Section 6: Products for Aviation Hazards Page 6-14
Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009)
• Phenomenon and its description (e.g., SEV TURB).
• An indication whether the information is observed, using OBS and/or FCST. The time of observation will be given in UTC.
• Location of the phenomenon referring, where possible to latitude and longitude, and flight levels (altitude) covering the affected area during the SIGMET valid time.
SIGMETs for volcanic ash cloud and tropical cyclones contain the positions of the ash cloud, tropical cyclone center and radius of convection at the start of the validity time of the SIGMET.
• Movement towards or expected movement using sixteen points of the compass, with speed in knots, or stationary, if appropriate.
• Thunderstorm maximum height as FL.
• Changes in intensity; using as appropriate, the abbreviations Intensifying (INTSF), Weakening (WKN), or No Change (NC).
• Forecast position of volcanic ash cloud or the center of the tropical cyclone at the end of the validity period of the SIGMET message.
AC 00-45F, CHG 2 Section 6: Products for Aviation Hazards Page 6-15
Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009)
Figure 6-7. SIGMET Outside the Conterminous U.S. Decoding Example
Table 6-3. Decoding a SIGMET Outside of the Conterminous U.S. (O-CONUS) Line Content Description 1 WSPA07 ICAO communication header PHFO Issuance MWO 010410 Issuance UTC date/time 2 SIGPAT NWS AWIPS communication header 3 KZOA Area Control Center SIGMET Product type TANGO SIGMET series 2 Issuance number VALID 010410/010800 Valid period UTC date/time PHFO Issuance office 4 OAKLAND OCEANIC FIR Flight Information Region (FIR) FRQ TS OBS AND FCST WI 200NM N3006 W14012 - N2012 W15016 CB TOP FL400 MOV W 10KT WKN.
Phenomenon description
The SIGMET in Figure 6-7 is decoded as the following:
(Line 1) The WMO product header is WSPA07. Issued by the PHFO on the 1st day of the month at 0410 UTC.
(Line 2) The NWS AWIPS communication header is SIGPAT.
(Line 3) For the Oakland (KZOA) Area Control Center. This is the 2nd issuance of SIGMET Tango series, valid from the 1st day of the month at 0410 UTC until the 1st day of the month at 0800 UTC, issued by the Honolulu Meteorological Watch Office.
AC 00-45F, CHG 2 Section 6: Products for Aviation Hazards Page 6-16