Reports, Forecasts & Advisories

Surface observations — METAR & SPECI

• METAR — routine surface observation. Issued hourly (typically 5 min before the hour) at most reporting stations. Read at aviationweather.gov/metar.
• SPECI — special METAR issued when conditions change significantly between routine observations (visibility crosses VFR/IFR thresholds, wind shift, thunderstorm onset, etc.).
• Reports the actual observed conditions: wind, visibility, weather, sky condition, temperature, dewpoint, altimeter, remarks.

METARs are observation, not forecast. The newest METAR is the most accurate ground truth for that field at that moment. They expire fast.

Terminal forecasts — TAF

• Forecast for a 5 SM radius around the airport. Issued 4× daily (00, 06, 12, 18 UTC) for major airports.
• Standard validity: 24 hours at smaller airports, 30 hours at major hubs.
• Change groups: FM (rapid permanent change at given time), BECMG (gradual change over a window), TEMPO (temporary fluctuations within the period), PROB30/40 (probability of hazardous weather).
• Wind shear groups appear as WS + altitude (in hundreds of feet AGL) + wind. Example: WS020/24050KT = wind shear at 2,000 ft, wind 240° at 50 kt.

Area forecasts — GFA

The textual Area Forecast (FA) for the CONUS has been replaced by the Graphical Forecasts for Aviation (GFA). The GFA shows synopsis, clouds, weather, icing, turbulence, and winds aloft on map layers, time-stepped from now to 15 hours out.

• Use it to spot regional hazards your METAR / TAF won't show — e.g., a developing line of cells along a frontal boundary 100 NM from your route.
• The icing layer fuses freezing-level forecasts with cloud forecasts to highlight icing risk by altitude.
• Textual area forecasts for Alaska, Hawaii, Caribbean, and offshore are still issued — see aviationweather.gov.

SIGMETs — significant meteorological information

• SIGMET (S-series): severe weather affecting all aircraft. Issued for severe icing not associated with TS, severe or extreme turbulence not associated with TS, dust/sandstorms reducing visibility < 3 SM, volcanic ash. Valid 4 hours (6 for hurricanes).
• Convective SIGMET (WST): thunderstorm-specific SIGMET for the CONUS. Issued every 55 minutes (and as needed). Covers TSs producing severe surface wind, hail ≥ 3/4", embedded TSs, lines of TSs, or any tornado. Valid 2 hours.
• International SIGMETs follow the same scheme but use ICAO conventions.

Read the current product list at aviationweather.gov/sigmet.

AIRMETs — airmen's meteorological information

Less severe than SIGMETs but more common. Three concurrent series, all valid 6 hours:

• Sierra — IFR conditions and mountain obscuration. Ceilings < 1,000 ft and/or visibility < 3 SM over 50% of the area, or extensive mountain obscuration.
• Tango — turbulence and surface winds > 30 kt. Includes moderate turbulence and sustained surface winds > 30 kt.
• Zulu — icing and freezing levels. Moderate icing and/or freezing level data.

"STZ" — Sierra, Tango, Zulu — is the easy mnemonic. AIRMETs apply specifically to operators using light aircraft (the FAA's stated audience).

Pilot reports — PIREP & AIREP

• PIREP (UA): routine pilot report. Most accurate real-time data for cloud bases/tops, turbulence, icing — anything observed.
• Urgent PIREP (UUA): tornado/funnel cloud, severe or extreme turbulence, severe icing, hail, low-level wind shear (more than 10 kt change in airspeed below 2,000 AGL), volcanic eruption.
• AIREP: automated pilot report from airliner-grade equipment. Same data, no human filtering.

File PIREPs through Flight Service (1-800-WX-BRIEF) or any controlling ATC facility. The product is only as good as the volume of reports — file every flight, even when conditions are nominal.

Decision framework — which product owns which question