Warnings, advisories & briefing

Is moderate turbulence alone a SIGMET phenomenon?

The European/ICAO product must be distinguished from US domestic warning conventions.

Purpose, issuer and phenomena

A SIGMET is issued by the responsible meteorological watch office for specified observed or forecast en-route phenomena which may affect aircraft safety. The ICAO/EASA list includes qualifying thunderstorms with or without hail (obscured, embedded, frequent or in a squall line), tropical cyclones, severe turbulence, severe icing including freezing rain, severe mountain wave, heavy duststorm/sandstorm, volcanic ash cloud and radioactive cloud. The qualifiers matter: ordinary moderate turbulence alone is not the severe-turbulence SIGMET trigger.

OBSC describes obscured thunderstorms, EMBD embedded thunderstorms, FRQ frequent coverage and SQL a squall line. GR adds hail. These describe hazard organisation/visibility, not a guarantee that a visible isolated cell is safe. Icing and turbulence associated with qualifying thunderstorms are inherent hazards and are not made harmless by absence of a separate symbol in the same warning. Do not import the US separation of domestic convective SIGMET into the European scheme.

SIGMET validity is normally at most four hours; volcanic-ash and tropical-cyclone SIGMET can extend to six hours. Only one specified phenomenon is included per SIGMET; the inherent turbulence/icing with thunderstorms or a tropical cyclone is not separately listed in that message. A tropical-cyclone SIGMET uses the specified surface-wind threshold of at least 34 kt. Check amendments, successor messages and cancellations, not just a stored number. Absence or expiry of a warning does not establish that every small-scale hazard has disappeared. The warning should be cancelled when its phenomenon is no longer occurring or expected in the covered area, but a particular message cancellation does not cancel every other active warning.

Does MOV E 20KT mean the wind is from the east?

Separate the event’s motion from the local air movement and the validity from observation time.

An original fictional SIGMET

Teaching message: YUCC SIGMET A02 VALID 211200/211600 YUDO- YUCC DONLON FIR SEV TURB OBS AT 1150Z WI N5200 E00200 - N5200 E00600 - N4900 E00600 - N4900 E00200 - N5200 E00200 FL320/380 MOV E 20KT INTSF=. YUCC identifies the fictional FIR/ATS area, SIGMET A02 its sequence (one letter and two numbers under the European requirement) and YUDO the issuing watch office in this exercise. It is valid on day 21 from 1200Z to 1600Z.

SEV TURB is severe turbulence, observed at 1150Z. WI gives a closed horizontal polygon using latitude/longitude; FL320/380 supplies its vertical extent. MOV E 20KT means the phenomenon moves towards the east at 20 kt, not a wind from 090°. INTSF means intensifying, WKN weakening and NC no change; STNR would mean stationary. An OBS time before validity is not the same as a forecast position at the end of validity.

Plot the polygon and its levels against the route and expected crossing time, then read any explicit forecast-position information and updates. A forecast graphic is another representation of the same event and must retain time, levels, coordinates and legend. Avoid extrapolating a simplified polygon rigidly for hours when growth and uncertainty matter. A clearance from ATC does not establish an acceptable meteorological crossing of the warned volume.

Can a low route be affected without a SIGMET?

AIRMET complements the area forecast where that service is provided.

What AIRMET adds

AIRMET describes specified observed or forecast hazards to low-level flight which were not included in the applicable low-level area forecast and warrant an update under the service arrangements. Its normal domain is below FL100, extended to FL150 in mountainous areas or higher where necessary. Regional products can have a stated broader limit; Spain’s published low-level service uses FL150. Read the responsibility area, valid period and local service rather than applying one universal ceiling.

Typical categories include widespread surface wind above 30 kt, widespread surface visibility below 5,000 m with the cause, mountain obscuration, widespread low broken/overcast cloud with base below 1,000 ft above ground, specified isolated/occasional thunderstorms, CB/TCU cloud, moderate icing, moderate turbulence and moderate mountain wave. The applicable template determines the exact cloud/convection qualifiers. AIRMET is not merely a weaker adjective applied to every SIGMET phenomenon, and a moderate icing AIRMET can be very important to an inadequately equipped aircraft.

A fictional AIRMET fragment MOD ICE FCST ... FL050/090 STNR NC describes forecast moderate icing between FL050 and FL090, stationary with no change. Decode its full header/time/area as for a SIGMET. AIRMET validity is at most four hours in the European framework. Check the area forecast, relevant SIGMET and subsequent changes together; no AIRMET is not evidence that the region has no low-level hazards or that the service exists at every aerodrome.

Does HAZARDOUS WX NIL mean clear sky and unlimited visibility?

Section I identifies specified hazards; Section II supplies the surrounding forecast environment.

Structure and interpretation

GAMET is an abbreviated plain-language area forecast for low-level flights over a defined region, with an issuing office, validity, area and vertical domain. The standard framework pairs a six-hourly six-hour-valid area forecast with AIRMET where applicable; other designated regional service arrangements can differ. The header and local AIP specify the actual coverage and schedule.

SECN I gives safety-significant low-level conditions: qualifying surface wind/visibility, significant weather, mountain obscuration, significant low cloud, icing, turbulence, mountain wave and applicable SIGMET information as required. SECN II gives additional information such as pressure systems, wind/temperature by level, other cloud layers, freezing-level height and minimum QNH. A section marker is not a change in forecast validity, and cloud information in the second section can still be operationally important.

Original fragment: SECN I SFC VIS: 12/15 3000M RA BR MT OBSC: N OF N5000 ICE: MOD FL050/090 SECN II FZLVL: 5000FT AMSL MNM QNH: 1002HPA. For 1200–1500Z, the stated visibility is 3 km in rain/mist; mountains north of 50°N are obscured; moderate icing is forecast in the stated layer. The freezing-level height is 5,000 ft AMSL, not 5,000 ft above every ridge. MNM QNH is a regional forecast minimum, not necessarily the actual current setting at a chosen airport. HAZARDOUS WX NIL concerns the specified Section I hazards under its rules; it does not promise a cloudless region or replace Section II and current reports.

What can ARS and VA ADVISORY each tell you?

One is an aircraft sample; the other assembles evidence and forecasts the ash distribution.

ARS in a briefing

A disseminated special air-report can identify ARS, aircraft identification, position, observation time, level and the significant condition. A fictional report of severe turbulence at FL350 near a named fix at 1150Z describes an encounter there and then; it does not prove that the entire FIR, all levels or the present time have the same state. Read the actual time/position/level and the reporting context before comparing it with a SIGMET or forecast grid.

The pilot’s reporting obligations include the specified SERA special observations, with their different qualifiers, and other safety-significant non-routine weather. A report can be useful even before an area warning is issued. The reporting aircraft’s type and response help interpret subjective intensity, while an automated EDR value has its own measurement definition. Preserve source and quality rather than merging all reports into one undated hazard icon.

Volcanic ash advisory fields and graphics

A VA ADVISORY identifies the VAAC, date/time group, volcano and position, summit elevation, advisory number, information source, eruption details, observation/estimated ash time and cloud layers, forecast ash positions at stated lead times, remarks and next-advisory time. SFC/FL150 and FL150/300 describe different vertical layers; their polygons can differ. Forecast +6HR, +12HR and +18HR positions must be attached to their corresponding UTC times, not overlaid as if all were observed simultaneously.

Original abbreviated exercise: OBS VA DTG: 21/1200Z; OBS VA CLD: FL150/300 WI a stated polygon; FCST VA CLD +6HR: 21/1800Z with a second polygon. A FL200 route is inside the given vertical layer; whether it crosses the ash also depends on location and time. In a graphical advisory, select the correct observation/forecast panel and layer legend. Absence of a drawn cloud elsewhere is limited by detection and modelling; it is not a certification of zero ash or an aircraft exposure limit. Read the relevant SIGMET, current operational information and operator/aircraft guidance as well.

Which fields describe position, motion and intensity?

Written and graphical advisories must be read with their issue time and forecast steps.

TC advisory decoding

The EASA service criterion calls for a TC advisory when the maximum 10-minute mean surface wind is expected to reach or exceed 34 kt during the advisory period. Compare other basin products only after checking their averaging convention. A tropical cyclone advisory identifies the issuing TCAC, date/time group, cyclone name or identifier, advisory number, observation time, centre position, movement, central pressure and maximum surface wind, followed by forecast centre positions and intensity for stated lead times, remarks and next update. Read hemisphere and coordinate format: N1800 E14000 is 18°00′N,140°00′E, not 18.00° and 140.00° in an arbitrary decimal scheme. Movement NW 15KT means towards northwest at 15 kt.

Original abbreviated case: OBS PSN N1800 E14000; MOV NW 15KT; C 1000HPA; MAX WIND 50KT; FCST PSN +6HR N1900 E13900; FCST MAX WIND +6HR 55KT. The centre is forecast farther north and west, with maximum wind increasing from 50 to 55 kt under that product’s averaging convention. Central pressure is not the local QNH at every surrounding airport. The forecast wind value is not the translation speed of the cyclone.

On a graphic, match each forecast centre marker to its UTC time and any intensity label; read the legend for uncertainty envelopes and wind radii if present. A plotted track is the expected centre path, not the full hazard boundary, and a cone is not a map of all dangerous weather. Rain, embedded convection, turbulence and damaging wind can extend far away and occur before the centre arrives. Read current advisories, TC SIGMET, aerodrome information and operational constraints; do not create a safe route by simply staying outside the line connecting the centres.

Does a ground-handling warning describe only the final approach?

Aerodrome warnings and wind-shear warnings/alerts serve different purposes.

Local warning products

An aerodrome warning gives concise information about observed or expected conditions which could adversely affect aircraft on the ground, including parked aircraft, and aerodrome facilities/services. Depending on local arrangements, phenomena include thunderstorms, squalls, strong surface wind/gusts, snow/freezing precipitation, frost, volcanic ash deposition and other relevant hazards. Read the aerodrome, warning number, valid interval, phenomenon, observed/forecast status, intensity and cancellation.

Original local-warning fragment: YUDO AD WRNG 2 VALID 211230/211530 SFC WIND 240/35KT MAX 50 FCST INTSF. It forecasts surface wind from 240° at 35 kt with maximum 50 kt during the stated day 21 interval, intensifying. It has implications for aircraft handling, parking, equipment and the local operation; it is not an en-route SIGMET or a new observed METAR.

A wind-shear warning describes observed or expected wind shear potentially affecting arrival/departure or circling in the low-level terminal region, including approach/take-off paths and the runway. The customary focus below 500 m/1,600 ft does not make shear above that height harmless. A warning can be based on pilot reports or meteorological detection/forecasting. In the European requirement, wind-shear alerts concern an observed headwind/tailwind change of 15 kt or more that could adversely affect the specified approach/take-off/runway operation. An automated alert is a timely detection output, often including a gain/loss and the affected runway/path location. Read whether it concerns approach or departure, its time and source; an alert’s numerical loss is not a universal prediction of exactly what every aircraft will experience.

A teaching alert such as RWY 27L ARRIVAL MICROBURST ALERT 30KT LOSS 2NM FINAL identifies the arrival path, microburst indication, reported/detected 30 kt loss and location 2 NM on final in that fictional system. It is not an instruction to continue until that point or an assured recovery margin. Apply the current type/operator wind-shear avoidance/recovery procedures and coordinate the decision. No alert can cover all sensor gaps, and the absence of a warning cannot nullify a credible encounter report.

Will ATIS necessarily give the full destination TAF?

Listen for the report’s time and scope, not just a familiar station identifier.

VOLMET and ATIS

VOLMET supplies meteorological information to aircraft in flight for a published set of aerodromes/areas. Continuous VHF VOLMET commonly carries current METAR/SPECI and TREND where available; exact content, coverage, update and frequency are published regionally. It is useful for checking destination/alternate conditions but is not a complete personalised route briefing or an ATC clearance. Note the observation time in the broadcast, especially when conditions change rapidly.

ATIS is an automatic terminal information service for a particular aerodrome or terminal operation. Its meteorological content includes relevant runway-representative wind, visibility/RVR, present weather, cloud/vertical visibility, temperature/dew point, QNH and significant information such as available TREND or wind-shear reports, together with operational items such as runway/approach in use and relevant runway conditions. Identify the information letter and time and confirm the latest version as required. D-ATIS provides the service by data link.

ATIS does not automatically include the complete TAF, every SIGMET along the route or all alternate forecasts. A VOLMET METAR and a current ATIS/tower runway report may differ because of update time, averaging and representative area. Compare like quantities and references, and ask for missing information. An information letter tells ATS which broadcast you received; it is not a guarantee that every value will remain valid until landing.

Does HF VOLMET always have exactly the VHF content?

Scheduled regional services support flights beyond convenient VHF coverage.

HF VOLMET and D-VOLMET

Scheduled VOLMET broadcasts, normally on HF, carry current METAR/SPECI with TREND where available and, where the regional agreement specifies, TAF and SIGMET. The set/order of aerodromes, time slots, frequencies and additional content are published in the relevant AIP/service information. Thus the presence of TAF/SIGMET must be checked for that service; neither every HF broadcast nor every VHF broadcast has one universal package.

HF propagation, interference and listening workload can affect reception. Check the broadcast identifier/time slot, capture the aerodrome and report-validity times, and resolve an incomplete group rather than guessing from a partial transmission. A forecast TAF validity must not be replaced with the broadcast time; an older observed METAR remains an older observation even when repeated on a new cycle.

D-VOLMET supplies meteorological products by data link according to the service, including reports, forecasts, warnings and relevant special air-reports/AIRMET where provided. It can reduce transcription work, but latency, coverage, aircraft equipment and provider capability still matter. Do not treat the last received message as the newest available merely because it is displayed digitally. Obtain appropriate ATS/meteorological assistance if critical information is missing.

What information changes the route, level, time or alternate?

A good briefing explains the meteorological situation, its uncertainty and the relevant alternatives.

Briefing, consultation and flight documentation

Meteorological briefing presents the current/expected situation, while consultation permits discussion with a qualified meteorological service about questions, uncertainty or conditions needing interpretation. Supply the route, flight date/times, aircraft capabilities, planned levels, departure/destination/alternates and operational concerns. A generic regional summary can miss a low-level segment, a delayed arrival or an alternate outside the initial map area.

Pre-flight information can include surface and upper-air analyses/forecasts, upper wind/temperature, SIGWX and low-level area forecasts, METAR/SPECI/TREND/TAF, SIGMET/AIRMET, air-reports, radar/satellite and specialist ash/TC advisories. Relevant aerodrome/wind-shear warnings and current runway-condition/operational information complete the decision context. Check product issue/observation/valid times, geographical/vertical coverage, updates and missing elements. Flight documentation records the relevant products; it is not a promise that the weather will match them exactly.

For a designated route, identify each hazard’s horizontal extent, vertical layer and expected crossing time, including climb/descent and alternates. Compare aircraft limitations, required equipment, applicable weather/alternate planning rules, fuel and performance using approved procedures. Choose a viable route/level/departure time and alternatives; define the observations or changes that would prompt replanning. A planning app’s green summary is not a substitute for the underlying branch conditions or an explicit decision.

Which update changes continuation towards the destination?

In-flight information must be related to the aircraft’s new position, timing and remaining alternatives.

Information available during flight

Flight information services and ATS can relay relevant updated SIGMET/AIRMET, aerodrome reports/forecasts, special air-reports and other available weather information; VOLMET, ATIS/D-ATIS and authorised data-link/briefing services provide additional updates according to coverage. Request what is needed, including report time and the actual message, rather than accepting an undated verbal summary as a complete route assessment. ATS availability of a product is not guaranteed everywhere.

Apply updates to remaining legs, revised ETA, levels, destination and usable alternates. A new forecast of worsening destination visibility, a credible wind-shear report or an unforecast ash area may invalidate the original plan. Compare the time window, aircraft/crew limitations, fuel/endurance and diversion distances using the applicable procedures. Decide early enough to preserve a suitable alternative and the required reserves; weather information does not itself waive fuel, approach or alternate requirements.

Example: the destination report deteriorates and its TAF amendment covers the revised ETA with below-usable conditions under the applicable operation, while the nearest suitable alternate is becoming more distant behind the aircraft. Do not continue simply because the original dispatch package was favourable. Verify current data, assess the suitable alternate and fuel promptly, coordinate with ATS/operations as applicable, and divert or take another justified action while the option remains. Report significant unforecast conditions you encounter so others can benefit.

Can you apply the ideas?

Four original questions. Decide from the facts, then review the explanation.