[{"data":1,"prerenderedAt":571},["ShallowReactive",2],{"learn-\u002Flearn\u002Fhow-to-read-a-sigmet-and-airmet":3,"learn-nav-\u002Flearn\u002Fhow-to-read-a-sigmet-and-airmet":533},{"id":4,"title":5,"body":6,"date":462,"description":463,"draft":464,"extension":465,"faqs":466,"howTo":476,"keyTakeaways":486,"meta":487,"navigation":488,"path":489,"quiz":490,"seo":516,"series":517,"seriesOrder":518,"sources":519,"stem":530,"topic":531,"__hash__":532},"learn\u002Flearn\u002Fhow-to-read-a-sigmet-and-airmet.md","How to read a SIGMET and an AIRMET",{"type":7,"value":8,"toc":451},"minimark",[9,27,33,38,51,73,77,90,187,198,202,239,243,246,251,254,349,353,381,392,396,436,440],[10,11,12,13,20,21,26],"p",{},"A ",[14,15,19],"a",{"href":16,"className":17},"\u002Flearn\u002Fglossary#gt-sigmet",[18],"glossary-link","SIGMET"," and an ",[14,22,25],{"href":23,"className":24},"\u002Flearn\u002Fglossary#gt-airmet",[18],"AIRMET"," are short coded warnings about weather that is hazardous in flight, and knowing which is which tells you at a glance how serious the threat is.",[28,29,30],"blockquote",{},[10,31,32],{},"This is general educational information, not operational, legal, or regulatory advice. Rules differ by authority and change over time. Always verify against current official sources and follow your operator's approved procedures.",[34,35,37],"h2",{"id":36},"what-each-one-warns-of","What each one warns of",[10,39,12,40,43,44,47,48,50],{},[41,42,19],"strong",{}," (significant meteorological information) warns of weather phenomena that are hazardous to ",[41,45,46],{},"all aircraft",": severe turbulence, severe icing, thunderstorms, volcanic ash, tropical cyclones, and similar threats. An ",[41,49,25],{}," (airmen's meteorological information) covers less severe en-route weather that still matters, especially to lighter aircraft and to flight under visual flight rules: moderate turbulence, moderate icing, widespread areas of reduced visibility or low cloud, and strong surface winds.",[10,52,53,54,60,61,66,67,72],{},"Both are international products. The requirement to issue them, and the structure of the message, come from ",[14,55,59],{"href":56,"rel":57},"https:\u002F\u002Fstore.icao.int\u002Fen\u002Fannex-3-meteorological-service-for-international-air-navigation-1",[58],"nofollow","ICAO Annex 3",", with the code form set out in the ",[14,62,65],{"href":63,"rel":64},"https:\u002F\u002Flibrary.wmo.int\u002Frecords\u002Fitem\u002F35713-manual-on-codes-international-codes-volume-i-1",[58],"WMO Manual on Codes (WMO No. 306)",". They are issued by a designated meteorological watch office for a flight information region (FIR), and they cover the airspace, not a single aerodrome. In the United Kingdom, SIGMETs for the UK FIRs are issued by the ",[14,68,71],{"href":69,"rel":70},"https:\u002F\u002Fwww.metoffice.gov.uk\u002Fservices\u002Ftransport\u002Faviation\u002Fregulated\u002Ftraining-resources-for-aviation\u002Fsigmets",[58],"Met Office"," acting as the meteorological watch office.",[34,74,76],{"id":75},"the-phenomena-codes","The phenomena codes",[10,78,79,80,83,84,89],{},"A SIGMET names the hazard with a short abbreviation. The common en-route phenomena, drawn from the ",[14,81,59],{"href":56,"rel":82},[58]," template and corroborated by the ",[14,85,88],{"href":86,"rel":87},"https:\u002F\u002Faviationweather.gov\u002Fhelp\u002Fdata\u002F",[58],"NOAA\u002FNWS Aviation Weather Center",", include:",[91,92,93,121,129,141,149,163,171,179],"ul",{},[94,95,96,99,100,104,105,108,109,112,113,116,117,120],"li",{},[41,97,98],{},"Thunderstorms",", qualified as ",[101,102,103],"code",{},"OBSC"," (obscured), ",[101,106,107],{},"EMBD"," (embedded), ",[101,110,111],{},"FRQ"," (frequent), or ",[101,114,115],{},"SQL"," (squall line), with ",[101,118,119],{},"GR"," added for hail.",[94,122,123,128],{},[41,124,125],{},[101,126,127],{},"SEV TURB"," for severe turbulence.",[94,130,131,136,137,140],{},[41,132,133],{},[101,134,135],{},"SEV ICE"," for severe icing, with ",[101,138,139],{},"(FZRA)"," if it is due to freezing rain.",[94,142,143,148],{},[41,144,145],{},[101,146,147],{},"SEV MTW"," for severe mountain waves.",[94,150,151,156,157,162],{},[41,152,153],{},[101,154,155],{},"HVY DS"," and ",[41,158,159],{},[101,160,161],{},"HVY SS"," for heavy dust storms and sandstorms.",[94,164,165,170],{},[41,166,167],{},[101,168,169],{},"VA"," for volcanic ash, usually with the volcano's name.",[94,172,173,178],{},[41,174,175],{},[101,176,177],{},"TC"," for a tropical cyclone, with its name.",[94,180,181,186],{},[41,182,183],{},[101,184,185],{},"RDOACT CLD"," for a radioactive cloud.",[10,188,189,190,193,194,197],{},"An AIRMET uses the same grammar at a lower intensity, for example ",[101,191,192],{},"MOD TURB"," for moderate turbulence or ",[101,195,196],{},"MOD ICE"," for moderate icing, plus broad areas of cloud and reduced visibility.",[34,199,201],{"id":200},"how-long-they-stay-valid","How long they stay valid",[10,203,204,205,208,209,212,213,216,217,221,222,225,226,228,229,234,235,238],{},"A SIGMET is normally valid for up to ",[41,206,207],{},"4 hours",". For the two longest-lead hazards, volcanic ash and tropical cyclones, the validity extends to up to ",[41,210,211],{},"6 hours",", as ",[14,214,59],{"href":56,"rel":215},[58]," provides and the ",[14,218,220],{"href":86,"rel":219},[58],"Aviation Weather Center"," confirms in US practice (where the 6-hour case is described as hurricanes). ",[14,223,59],{"href":56,"rel":224},[58]," caps AIRMET validity at no more than ",[41,227,207],{},"; in the United States the ",[14,230,233],{"href":231,"rel":232},"https:\u002F\u002Fwww.faa.gov\u002Fair_traffic\u002Fpublications\u002Fatpubs\u002Faim_html\u002Fchap7_section_1.html",[58],"FAA"," issues AIRMETs on a ",[41,236,237],{},"6-hour"," schedule, so the 6-hour figure is a US convention rather than the ICAO baseline. Whichever you are reading, treat it as a moving picture: a new issue supersedes the old one, so brief from the latest.",[34,240,242],{"id":241},"a-worked-sigmet","A worked SIGMET",[10,244,245],{},"Here is a SIGMET in the standard ICAO format for the London FIR:",[10,247,248],{},[101,249,250],{},"EGTT SIGMET 2 VALID 181200\u002F181600 EGRR- EGTT LONDON FIR SEV TURB FCST WI N5130 W00100 - N5200 E00030 - N5100 E00100 - N5030 W00030 - N5130 W00100 FL250\u002F350 MOV E 25KT WKN=",[10,252,253],{},"Reading it through:",[91,255,256,262,268,274,280,286,291,301,307,319,329,343],{},[94,257,258,261],{},[101,259,260],{},"EGTT"," is the location indicator of the flight information region the SIGMET covers, here the London FIR.",[94,263,264,267],{},[101,265,266],{},"SIGMET 2"," is the message type and sequence number: the second SIGMET issued for that FIR in the current series.",[94,269,270,273],{},[101,271,272],{},"VALID 181200\u002F181600"," is the validity period in UTC: from the 18th at 1200 until the 18th at 1600, a 4-hour SIGMET.",[94,275,276,279],{},[101,277,278],{},"EGRR-"," identifies the issuing meteorological watch office (the UK Met Office at Exeter).",[94,281,282,285],{},[101,283,284],{},"EGTT LONDON FIR"," repeats the affected region in plain form.",[94,287,288,290],{},[101,289,127],{}," is the phenomenon: severe turbulence.",[94,292,293,296,297,300],{},[101,294,295],{},"FCST"," says the phenomenon is forecast. The alternative is ",[101,298,299],{},"OBS"," for observed, sometimes with a time.",[94,302,303,306],{},[101,304,305],{},"WI"," introduces the area, bounded by the latitude and longitude points that follow, which close back to the first point to form a polygon.",[94,308,309,312,313,318],{},[101,310,311],{},"FL250\u002F350"," is the vertical extent: between ",[14,314,317],{"href":315,"className":316},"\u002Flearn\u002Fglossary#gt-flight-level",[18],"flight level"," 250 and flight level 350.",[94,320,321,324,325,328],{},[101,322,323],{},"MOV E 25KT"," is the movement: moving east at 25 knots. A system that is not moving reads ",[101,326,327],{},"STNR"," for stationary.",[94,330,331,334,335,338,339,342],{},[101,332,333],{},"WKN"," is the expected intensity trend: weakening. The alternatives are ",[101,336,337],{},"INTSF"," (intensifying) and ",[101,340,341],{},"NC"," (no change).",[94,344,345,348],{},[101,346,347],{},"="," marks the end of the message.",[34,350,352],{"id":351},"the-icao-baseline-and-the-us-additions","The ICAO baseline and the US additions",[10,354,355,356,360,361,364,365,368,369,372,373,376,377,380],{},"The ICAO SIGMET and AIRMET are the international baseline, but the United States layers extra products on top, and you should not assume they exist elsewhere. Per the ",[14,357,359],{"href":231,"rel":358},[58],"FAA Aeronautical Information Manual",", the FAA issues domestic AIRMETs in three named types: ",[41,362,363],{},"Sierra"," for instrument conditions and mountain obscuration, ",[41,366,367],{},"Tango"," for turbulence and strong surface winds, and ",[41,370,371],{},"Zulu"," for icing and freezing levels. It also publishes a ",[41,374,375],{},"G-AIRMET",", the same hazards drawn as graphical snapshots at fixed times rather than as one continuous-validity bulletin, as the ",[14,378,220],{"href":86,"rel":379},[58]," describes.",[10,382,383,384,387,388,391],{},"The most important US-only product is the ",[41,385,386],{},"Convective SIGMET",", issued for thunderstorm-related hazards (lines of thunderstorms, embedded storms, large areas of storms, and severe weather). It is a distinct American product with its own short validity, so do not read it as an ICAO SIGMET or expect it abroad. Outside the United States, thunderstorm hazards are carried in the ordinary SIGMET using the ",[101,389,390],{},"TS"," codes above.",[34,393,395],{"id":394},"common-pitfalls","Common pitfalls",[91,397,398,415,421,430],{},[94,399,400,403,404,156,409,414],{},[41,401,402],{},"A SIGMET is an area warning, not an aerodrome report."," Pair it with the ",[14,405,408],{"href":406,"className":407},"\u002Flearn\u002Fglossary#gt-metar",[18],"METAR",[14,410,413],{"href":411,"className":412},"\u002Flearn\u002Fglossary#gt-taf",[18],"TAF"," for your aerodromes and with the area forecast for the route.",[94,416,417,420],{},[41,418,419],{},"Mind the validity window."," A SIGMET that expires before your arrival tells you nothing about your arrival; look for the reissue.",[94,422,423,426,427,429],{},[41,424,425],{},"The polygon and flight levels both matter."," A severe-turbulence SIGMET at ",[101,428,311],{}," does not constrain a piston aircraft at 8000 ft, but a low-level icing AIRMET very much does.",[94,431,432,435],{},[41,433,434],{},"Do not assume the US products exist everywhere."," Convective SIGMETs and the Sierra\u002FTango\u002FZulu naming are American.",[34,437,439],{"id":438},"in-pilot-efb","In Pilot EFB",[10,441,442,443,446,447,450],{},"Pilot EFB pulls the weather for your route and shows the ",[41,444,445],{},"decoded"," report alongside the ",[41,448,449],{},"raw"," text, with the raw warning always kept and never replaced, so you can trace a plain-language summary back to the original coded groups. A briefing you have already pulled stays readable with no signal, because your device holds what you have saved; fetching a fresh SIGMET or AIRMET needs a connection. Pilot EFB is offline-first and is not a certified Electronic Flight Bag, so brief the hazardous-weather picture from your official meteorological source of record.",{"title":452,"searchDepth":453,"depth":453,"links":454},"",2,[455,456,457,458,459,460,461],{"id":36,"depth":453,"text":37},{"id":75,"depth":453,"text":76},{"id":200,"depth":453,"text":201},{"id":241,"depth":453,"text":242},{"id":351,"depth":453,"text":352},{"id":394,"depth":453,"text":395},{"id":438,"depth":453,"text":439},"2026-06-18","What SIGMETs and AIRMETs warn of, the phenomena codes, how long each stays valid, and a worked SIGMET decoded field by field, with the ICAO baseline and the US differences.",false,"md",[467,470,473],{"q":468,"a":469},"What is the difference between a SIGMET and an AIRMET?","A SIGMET warns of weather hazardous to all aircraft, such as severe turbulence, severe icing, thunderstorms, volcanic ash or a tropical cyclone, while an AIRMET warns of less severe en-route weather that mainly affects lighter aircraft and visual flight, such as moderate turbulence, moderate icing or widespread reduced visibility. Both sit under the ICAO Annex 3 framework, and the United States adds extra products such as the Convective SIGMET.",{"q":471,"a":472},"How long is a SIGMET valid?","A SIGMET is normally valid for up to 4 hours, extended to up to 6 hours for volcanic ash and tropical cyclone SIGMETs, as ICAO Annex 3 sets out. In the United States the FAA issues 6-hour SIGMETs for hurricanes and 4-hour SIGMETs for the other phenomena.",{"q":474,"a":475},"What do the US AIRMET types Sierra, Tango and Zulu mean?","In the United States the FAA issues AIRMETs in three types: Sierra for instrument conditions and mountain obscuration, Tango for turbulence and strong surface winds, and Zulu for icing and freezing levels. The graphical G-AIRMET carries the same hazards as snapshots at fixed times rather than as one continuous bulletin.",{"name":477,"steps":478},"How to read a SIGMET",[479,480,481,482,483,484,485],"Identify the message: the flight information region or location indicator, the word SIGMET, and the sequence number.","Read the validity period, given as two day-hour-minute groups in UTC for the start and end.","Note the issuing meteorological watch office and the flight information region the warning covers.","Read the phenomenon, for example SEV TURB for severe turbulence or SEV ICE for severe icing.","Check whether the phenomenon is observed (OBS) or forecast (FCST).","Read the area: the coordinates of the polygon, and the vertical extent given as flight levels.","Read the movement and intensity: a direction and speed, or STNR for stationary, then INTSF, WKN or NC for the trend.",null,{},true,"\u002Flearn\u002Fhow-to-read-a-sigmet-and-airmet",[491,500,508],{"q":492,"options":493,"answer":498,"explanation":499},"What is the key difference between a SIGMET and an AIRMET?",[494,495,496,497],"A SIGMET warns of weather hazardous to all aircraft, while an AIRMET covers less severe en-route weather affecting mainly lighter aircraft and visual flight","A SIGMET is for aerodromes, while an AIRMET is for the en-route phase","A SIGMET is a US-only product, while an AIRMET is the ICAO baseline","A SIGMET is forecast only, while an AIRMET is observed only",0,"A SIGMET warns of weather hazardous to all aircraft, such as severe turbulence or icing, thunderstorms, volcanic ash and tropical cyclones, while an AIRMET covers less severe en-route weather that matters especially to lighter aircraft and to visual flight.",{"q":501,"options":502,"answer":453,"explanation":507},"In the ICAO framework, how long is a SIGMET for volcanic ash or a tropical cyclone normally valid?",[503,504,505,506],"Up to 2 hours","Up to 4 hours","Up to 6 hours","Up to 12 hours","A SIGMET is normally valid for up to 4 hours, but for the two longest-lead hazards, volcanic ash and tropical cyclones, the validity extends to up to 6 hours.",{"q":509,"options":510,"answer":453,"explanation":515},"In a SIGMET, what does the code SEV TURB indicate?",[511,512,513,514],"Severe icing","A squall line","Severe turbulence","A radioactive cloud","SEV TURB is the code for severe turbulence; severe icing is SEV ICE and a radioactive cloud is RDOACT CLD.",{"title":5,"description":463},"decode-the-weather",4,[520,522,524,526,528],{"label":521,"url":56},"ICAO Annex 3: Meteorological Service for International Air Navigation",{"label":523,"url":63},"WMO No. 306: Manual on Codes, Volume I.1",{"label":525,"url":231},"FAA Aeronautical Information Manual, Chapter 7 Section 1 (Meteorology)",{"label":527,"url":69},"UK Met Office: SIGMETs",{"label":529,"url":86},"NOAA\u002FNWS Aviation Weather Center: product descriptions","learn\u002Fhow-to-read-a-sigmet-and-airmet","Weather","J6ooA2h1-xihdZ26U_M0C-X2wCTjCG-GNBpGPlU6s7A",{"related":534,"newer":552,"older":545,"series":557},[535,541,545],{"path":536,"title":537,"description":538,"date":539,"topic":531,"draft":464,"minutes":540,"series":486,"seriesOrder":486},"\u002Flearn\u002Freading-a-surface-analysis-chart","How to read a surface analysis chart","Decode a surface analysis chart: isobars and the pressure gradient, highs and lows, warm, cold and occluded fronts, and what the big picture tells you before you read the METAR.","2026-06-20",3,{"path":542,"title":543,"description":544,"date":539,"topic":531,"draft":464,"minutes":540,"series":486,"seriesOrder":486},"\u002Flearn\u002Fthe-international-standard-atmosphere","The International Standard Atmosphere (ISA)","What the ICAO International Standard Atmosphere is, its sea-level values and lapse rate, and how ISA deviation underpins altimetry, performance and density altitude.",{"path":546,"title":547,"description":548,"date":549,"topic":531,"draft":464,"minutes":550,"series":517,"seriesOrder":551},"\u002Flearn\u002Fhow-to-read-a-metar","How to read a METAR","A plain-language guide to decoding a METAR field by field, with a worked example and the EASA\u002FUK and FAA differences that trip pilots up.","2026-06-17",5,1,{"path":553,"title":554,"description":555,"date":539,"topic":556,"draft":464,"minutes":540,"series":486,"seriesOrder":486},"\u002Flearn\u002Fwake-turbulence-categories-and-separation","Wake turbulence categories and separation","Why aircraft trail wingtip vortices, the ICAO Light, Medium, Heavy and Super categories by maximum take-off mass, and how wake separation keeps a following aircraft clear.","Operations",{"slug":517,"title":558,"part":518,"total":550,"prev":559,"next":565},"Decode the weather",{"path":560,"title":561,"description":562,"date":563,"topic":531,"draft":464,"minutes":564,"series":517,"seriesOrder":540},"\u002Flearn\u002Fhow-to-read-an-atis","How to read an ATIS","What the ATIS broadcast contains, how the information letter and runway-in-use work, how it differs from a METAR, and the EASA\u002FUK and FAA conventions that trip pilots up.","2026-04-07",7,{"path":566,"title":567,"description":568,"date":569,"topic":570,"draft":464,"minutes":518,"series":517,"seriesOrder":550},"\u002Flearn\u002Fhow-to-read-a-pirep","How to read a PIREP","Decode a pilot weather report field by field, understand the UA and UUA types and the slash-coded elements, and see how a PIREP fills the gaps between weather stations.","2026-06-07","Briefing",1781989190546]