SIGMET

Last updated

SIGMET, [1] or Significant Meteorological Information (AIM 7-1-6), [2] is a severe weather advisory that contains meteorological information concerning the safety of all aircraft. Compared to AIRMETs, SIGMETs cover more severe weather. Today, according to the advancement of technology in civil aviation, the SIGMET is sent as IWXXM model. [3]

Contents

Types

There are three main types of internationally recognized SIGMETs per ICAO: [4]

This information is usually broadcast on the ATIS at ATC facilities, as well as over VOLMET stations. They are assigned an alphabetic designator from N through Y (excluding S and T). [2] SIGMETs are issued as needed, and are valid up to four hours. SIGMETS for hurricanes and volcanic ash outside the CONUS are valid up to six hours. [5]

Convective SIGMETs

For airmen in the U.S., there is an additional category of SIGMET known as a convective SIGMET. These are issued for convection over the coterminous U.S.. There are three types of convective SIGMETs:

TypeDefinition
Line ThunderstormThunderstorms at least 60 miles long with thunderstorms affecting 40% of its length.
Area ThunderstormThunderstorms covering at least 40% of the area concerned and exhibiting a very strong radar reflectivity or a significant satellite or lightning signature.
Embedded ThunderstormEmbedded or severe thunderstorms expected to occur for more than 30 minutes.

There are also a few special issuance convective SIGMETs to cover extreme weather more common in the U.S., including

[6]

Structure

SIGMETs are internationally used by ICAO and WMOs using standardized abbreviations

AbbreviationMeaning
ABVAbove
CNLCancel or cancelled
CTAControl area
FCSTForecast
FIRFlight Information Region
FLFlight level
FTFeet
INTSFIntensify or intensifying
KTKnots
KMHKilometres per hour
MMetres
MOVMoving
NCNo Change (in intensity)
NMNautical Miles
OBSObserved
SFCSurface
STNRStationary
TOPTop (of CB cloud)
WIWithin (area)
WKNWeakening (intensity)
ZCoordinated Universal Time

and are split into three lines:

In sum, a standardized SIGMET will have the following structure:

TTAAii CCCC YYGGgg [BBB]CCCC SIGMET [n][n]n VALID YYGGgg/YYGGgg CCCC-CCCC <FIR/CTA Name> FIR <Phenomenon> OBS/FCST [AT GGggZ] <Location> <Level> [MOV XXX xx KT/KMH] [INTSF/WKN/NC] <Forecast time and forecast position>=

The header line consists of the following characters

TTAAii CCCC YYGGgg [CCx]

ComponentDescription
TTA data type identifier per the types of SIGMETs mentioned above. VA or WV for volcanic ash, TC for tropical cyclone, and WS otherwise.
AAThe two-character country or territory code of the alert.
iiBulletin number
CCCCThe 4-character ICAO location of the dissmenating office.
YYDay of the month.
GGHours UTC.
ggMinutes UTC.
[CCx]When included, indicates a correction that takes the form of CCx where x is A-Z indicating the correction number.

Summary

The first line of the broadcast is a summary line consisting of the following characters

CCCC SIGMET [n][n]n VALID YYGGgg/YYGGgg CCCC-

ComponentDescription
CCCCThe 4-character ICAO location of the affected area.
SIGMETIndicates that this is a SIGMET broadcast. [a]
[n][n]nA sequence number of the form 1', 01, A01, etc. which is incremented for each time the SIGMET remains effective past 0001UTC or upon renewals. Helps indicate how long the SIGMET has been active.
VALID YYGGgg/YYGGggIndicates the period the SIGMET is active (WS SIGMETs can not be active for more than 4 hours), where YY is the day of the month, GG is the hour, and gg is the minute.
CCCC-The 4-character ICAO location of the dissmenating office followed by a hyphen.
Notes
  [a] – if it a convective SIGMET, then this will read SIG[E/C/W] CONVECTIVE SIGMET ##[E/C/W]. Where E/C/W indicates whether it's over the Eastern, Central, or Western United States, and ## indicates the number of the convective SIGMET issued for that region.

Body

The main body of a SIGMET can be much more variable, and consists of

CCCC [FIR/CTA list] <Phenomenon> OBS/FCST [AT GGggZ] <Location> <Level> [MOV XXX xx KT/KMH] [INTSF/WKN/NC] [FCST AT <GGgg>Z <location>]=

CCCC [FIR/CTA list] is again the 4-character ICAO location, followed by the affected flight or control regions.

<Phenomenon> is a code describing the meteorological phenomena as follows:

CodeDescription
OBSC TSObscured thunderstorms
EMBD TSEmbedded thunderstorms
FRQ TSFrequent thunderstorms
SQL TSSquall line thunderstorms
OBSC TSGRObscured thunderstorms with hail
EMBD TSGREmbedded thunderstorms with hail
FRQ TSGRFrequent thunderstorms with hail
SQL TSGRSquall line thunderstorms with hail
SEV TURBSevere turbulence
SEV ICESevere icing
SEV ICE (FZRA)Severe icing due to freezing rain
SEV MTWSevere mountain wave
HVY DSHeavy duststorm
HVY SSHeavy sandstorm
RDOACT CLDRadioactive cloud

If it is a convective SIGMET, the following codes may appear

CodeDescription
AREA TSArea-wide thunderstorms
LINE TSThunderstorm line
EMBD TSEmbedded thunderstorms
TDOTornado
FCFunnel Cloud
WTSPTWaterspout
HVY GRHeavy Hail

[7]

OBS/FCST [AT GGggZ] indicates whether the phenomenon is observed (OBS) or forecasted (FCST), and the Zulu hour and minute that it was observed or will be forecasted.

<Location> is a general description of location of the meteorological phenomenon, typically utilizing latitude and longitudinal coordinates.

<Level> helps denote the altitude that the phenomenon will be occurred, and can be expressed as

FLnnn or nnnnM or nnnnFTAt a particular altitude
SFC/FLnnn or SFC/nnnnM or SFC/nnnnFTFrom the surface (SFC) to a particular altitude
FLnnn/nnn or nnnn/nnnnFTBetween certain altitudes
TOP FLnnn or ABV FLnnn or TOP ABV FLnnnAbove a certain point or cloud cover

[MOV XXX xx KT/KMH] if it is a moving front, the direction and rate of movement given as a compass direction (XXX, e.g. "N" or "WNW"), and the rate is given in KT (or KMH). Sometimes STNR (Stationary) may be used instead if no significant movement is expected.

[INTSF/WKN/NC] denotes the change in strength over time.

[FCST AT <GGgg>Z <location>] helps note where the front is expected to be at the end of the SIGMET's validity period.

SIGMET Renewal and Cancellation

If when the validity period is due to expire but the phenomenon is expected to persist, a new sequence number is added to the SIGMET to renew it.

If during the validity period of a SIGMET, the SIGMET is to be cancelled, the following replaces the SIGMET message

CNL SIGMET [n][n]n YYGGgg/YYGGgg [8]

Examples

WSUS32 KKCI 071655

An en-route weather phenomenon in the U.S., issued by the Aviation Weather Center in Kansas City, MO on the 7th of August, at 16:55 UTC [9]

SIGC CONVECTIVE SIGMET 83C

This is a convective weather pattern in the central region of the contiguous U.S. with sequence number 83C

VALID UNTIL 1855Z

That is valid until 18:55 UTC

MI IN WI IL IA LM

That covers Minnesota, Indiana, Wisconsin, Illinois, Iowa, and Lower Michigan flight regions

FROM 30E GRR-30S GIJ-30SSW BDF-10ENE IOW-50ENE DBQ-30E GRR

A description of the area of the storm, where GRR (Grand Rapids, MI airport), GIJ (Niles, MI VORTAC), BDF (Bradford, IL VORTAC), IOW (Iowa City, IA airport), and DBQ (Dubuque, IA airport) are ConTrol Areas (CTAs).

AREA TS MOV FROM 25025KT. TOPS TO FL450.

Thunderstorms moving from 250 degrees (roughly WSW) at 25 knots, covering an altitude from the cloud cover to 45,000 ft.

See also

Related Research Articles

<span class="mw-page-title-main">Lapse rate</span> Vertical rate of change of temperature in atmosphere

The lapse rate is the rate at which an atmospheric variable, normally temperature in Earth's atmosphere, falls with altitude. Lapse rate arises from the word lapse. In dry air, the adiabatic lapse rate is 9.8 °C/km. The saturated adiabatic lapse rate (SALR), or moist adiabatic lapse rate (MALR), is the decrease in temperature of a parcel of water-saturated air that rises in the atmosphere. It varies with the temperature and pressure of the parcel and is often in the range 3.6 to 9.2 °C/km, as obtained from the International Civil Aviation Organization (ICAO). The environmental lapse rate is the decrease in temperature of air with altitude for a specific time and place. It can be highly variable between circumstances.

<span class="mw-page-title-main">Tornado watch</span> Weather watch indicating conditions favorable for tornado development in severe thunderstorms

A tornado watch is a statement issued by weather forecasting agencies to advise the public that atmospheric conditions in a given region may lead to the development of tornadoes within the region over a period of several hours. In addition to the potential for tornado development, thunderstorms that develop within the watch area may contain large hail, straight-line winds, intense rainfall and/or flooding that pose a similar damage risk as the attendant tornado threat.

<span class="mw-page-title-main">Severe thunderstorm watch</span> Weather watch indicating conditions favorable for the development of severe thunderstorms

A severe thunderstorm watch is a statement issued by weather forecasting agencies to advise the public that atmospheric conditions in a given region may lead to the development of severe thunderstorms within the region over a period of several hours. The criteria for issuing a watch varies by country, and may also include torrential rainfall and tornadoes. A watch may also be issued several hours ahead of the arrival of a mature and organized complex of storms, or more clustered or discrete storm activity.

<span class="mw-page-title-main">National Weather Service</span> U.S. forecasting agency of the National Oceanic and Atmospheric Administration

The National Weather Service (NWS) is an agency of the United States federal government that is tasked with providing weather forecasts, warnings of hazardous weather, and other weather-related products to organizations and the public for the purposes of protection, safety, and general information. It is a part of the National Oceanic and Atmospheric Administration (NOAA) branch of the Department of Commerce, and is headquartered in Silver Spring, Maryland, within the Washington metropolitan area. The agency was known as the United States Weather Bureau from 1890 until it adopted its current name in 1970.

<span class="mw-page-title-main">Met Office</span> United Kingdoms national weather service

The Meteorological Office, abbreviated as the Met Office, is the United Kingdom's national weather and climate service. It is an executive agency and trading fund of the Department for Science, Innovation and Technology and is led by CEO Penelope Endersby, who took on the role as Chief Executive in December 2018 and is the first woman to do so. The Met Office makes meteorological predictions across all timescales from weather forecasts to climate change.

<span class="mw-page-title-main">Japan Meteorological Agency</span> National meteorological service of Japan

The Japan Meteorological Agency, a division of the Ministry of Land, Infrastructure, Transport and Tourism, is dedicated to the scientific observation and research of natural phenomena. Headquartered in Minato, Tokyo the agency diligently collects data on meteorology, hydrology, seismology, and volcanology, and other related fields. Through meticulous analysis and interpretation of this information, the JMA provides vital insights to the public, offering crucial knowledge and forecasts to enhance preparedness and mitigate risks associated with weather patterns, earthquakes, volcanic activities, and other natural occurrences.

<span class="mw-page-title-main">METAR</span> Format for weather reports commonly used in aviation

METAR is a format for reporting weather information. A METAR weather report is predominantly used by aircraft pilots, and by meteorologists, who use aggregated METAR information to assist in weather forecasting. Today, according to the advancement of technology in civil aviation, the METAR is sent as IWXXM model.

<span class="mw-page-title-main">Storm Prediction Center</span> American severe weather forecasting center

The Storm Prediction Center (SPC) is a US government agency that is part of the National Centers for Environmental Prediction (NCEP), operating under the control of the National Weather Service (NWS), which in turn is part of the National Oceanic and Atmospheric Administration (NOAA) of the United States Department of Commerce (DoC).

<span class="mw-page-title-main">Derecho</span> Widespread, long-lived, straight-line wind storm

A derecho is a widespread, long-lived, straight-line wind storm that is associated with a fast-moving group of severe thunderstorms known as a mesoscale convective system.

In meteorology and aviation, terminal aerodrome forecast (TAF) is a format for reporting weather forecast information, particularly as it relates to aviation. TAFs are issued at least four times a day, every six hours, for major civil airfields: 0000, 0600, 1200 and 1800 UTC, and generally apply to a 24- or 30-hour period, and an area within approximately five statute miles (8.0 km) from the center of an airport runway complex. TAFs are issued every three hours for military airfields and some civil airfields and cover a period ranging from 3 hours to 30 hours.

A pilot report or PIREP is a report of actual flight or ground conditions encountered by an aircraft. Reports commonly include information about atmospheric conditions or airport conditions. This information is usually relayed by radio to the nearest ground station, but other options also exist in some regions. The message would then be encoded and relayed to other weather offices and air traffic service units.

An AIRMET, or Airmen's Meteorological Information, is a concise description of weather phenomena that are occurring or may occur (forecast) along an air route that may affect aircraft safety. Compared to SIGMETs, AIRMETs cover less severe weather: moderate turbulence and icing, sustained surface winds of 30 knots or more, or widespread restricted visibility. Today, according to the advancement of technology in civil aviation, the AIRMET is sent as IWXXM model.

<span class="mw-page-title-main">Bounded weak echo region</span> Weather feature

The bounded weak echo region, also known as a BWER or a vault, is a radar signature within a thunderstorm characterized by a local minimum in radar reflectivity at low levels which extends upward into, and is surrounded by, higher reflectivities aloft, forming a kind of dome of weak echoes. This feature is associated with a strong updraft and is almost always found in the inflow region of a thunderstorm: it cannot be seen visually. The BWER has been noted on radar imagery of severe thunderstorms since 1973 and has a lightning detection system equivalent known as a lightning hole.

The Fiji Meteorological Service (FMS) is a Department of the government of Fiji responsible for providing weather forecasts and is based on the grounds of Nadi Airport in Nadi. The current director of Fiji Meteorological Service is Misaeli Funaki. Since 1985, FMS has been responsible for naming and tracking tropical cyclones in the Southwest Pacific region. Current Meteorologists working at FMS have a Graduate Diploma in Meteorology from the Australian Bureau of Meteorology.

A Center Weather Service Unit (CWSU) is a National Weather Service (NWS) unit located inside each of the Federal Aviation Administration's 22 Air Route Traffic Control Centers (ARTCC).

<span class="mw-page-title-main">Area forecast</span>

An Aviation Area Forecast was a message product of the National Weather Service (NWS) in the United States. It has been replaced by Graphic Area Forecasts, or GFA, in 2017.

<span class="mw-page-title-main">Surface weather observation</span> Fundamental data used for weather forecasts

Surface weather observations are the fundamental data used for safety as well as climatological reasons to forecast weather and issue warnings worldwide. They can be taken manually, by a weather observer, by computer through the use of automated weather stations, or in a hybrid scheme using weather observers to augment the otherwise automated weather station. The ICAO defines the International Standard Atmosphere (ISA), which is the model of the standard variation of pressure, temperature, density, and viscosity with altitude in the Earth's atmosphere, and is used to reduce a station pressure to sea level pressure. Airport observations can be transmitted worldwide through the use of the METAR observing code. Personal weather stations taking automated observations can transmit their data to the United States mesonet through the Citizen Weather Observer Program (CWOP), the UK Met Office through their Weather Observations Website (WOW), or internationally through the Weather Underground Internet site. A thirty-year average of a location's weather observations is traditionally used to determine the station's climate. In the US a network of Cooperative Observers make a daily record of summary weather and sometimes water level information.

<span class="mw-page-title-main">European Severe Storms Laboratory</span> Organization

The European Severe Storms Laboratory (ESSL) is a scientific organisation that conducts research on severe convective storms, tornadoes, intense precipitation events, and avalanches across Europe and the Mediterranean. It operates the widely consulted European Severe Weather Database (ESWD).

ICAO Meteorological Information Exchange Model (IWXXM) is a format for reporting weather information in XML/GML. IWXXM includes XML/GML-based representations for products standardized in International Civil Aviation Organization (ICAO) Annex III, such as METAR/SPECI, TAF, SIGMET, AIRMET, Tropical Cyclone Advisory (TCA), Volcanic Ash Advisory (VAA), Space Weather Advisory and World Area Forecast System (WAFS) Significant Weather (SIGWX) Forecast. IWXXM products are used for operational exchanges of meteorological information for use in aviation.

<span class="mw-page-title-main">Glossary of meteorology</span> List of definitions of terms and concepts commonly used in meteorology

This glossary of meteorology is a list of terms and concepts relevant to meteorology and atmospheric science, their sub-disciplines, and related fields.

References

  1. "AIM - page 634". www.faraim.org. Archived from the original on 2017-02-02.
  2. 1 2 "Pilot's Handbook of Aeronautical Knowledge". Federal Aviation Administration. Retrieved 17 September 2019.
  3. Latifiyan, Pouya; Entezari, Mojtaba (March 2024). "IWXXM Amendment (ICAO Meteorological Information Exchange Model)". CATC Robex and Statics Conferences - 2024. Tehran, Iran.
  4. "SIGMET explanation". IVAO Documentation Library.
  5. "AC 00-45H - Aviation Weather Services - Change 2 (Cancelled)" . Retrieved 2023-08-27.
  6. "ARC - AIRMETs/SIGMETs". NWS. Retrieved 2022-08-07.
  7. "Products for Aviation Hazards". Ascent Ground School.
  8. "SIGMET Quick Reference Guide" (PDF). ICAO.
  9. "COMMS-ID MESSAGE". COMMS-ID MESSAGE. National Weather Service. Retrieved 18 November 2023.