Airport Weather: METAR, TAF, SPECI and Flight Rules
Accurate and timely weather information is fundamental to safe and efficient aviation operations. Pilots, dispatchers, air traffic controllers, and airport operators rely on standardized weather reports and forecasts to assess current conditions, anticipate changes, and apply appropriate flight rules. The primary airport weather products are METAR, TAF, and SPECI, supported by clearly defined visual and instrument flight rules.
METAR – Aviation Routine Weather Report
A METAR is an observation of the current weather conditions at an airport or weather station. It is typically issued at regular intervals, usually every 30 or 60 minutes, and provides a real-time snapshot of operationally significant weather.
A METAR includes wind direction and speed, prevailing visibility, runway visual range when applicable, significant weather phenomena such as rain, fog, or thunderstorms, cloud coverage and cloud base heights, temperature and dew point, altimeter setting, and notable remarks. Because METARs reflect actual observed conditions, they are the primary reference for determining whether Visual Flight Rules (VFR) or Instrument Flight Rules (IFR) apply at a given moment.
Example METAR: METAR EGLL 121350Z 22012KT 9999 SCT025 18/12 Q1015
SPECI – Special Weather Report
A SPECI is a non-routine weather observation issued whenever significant changes occur between scheduled METAR reports. Its purpose is to immediately alert aviation users to rapidly changing or hazardous conditions.
SPECI reports are triggered by events such as sudden reductions in visibility or cloud ceiling, the onset or cessation of thunderstorms, freezing precipitation, wind shear, or substantial wind changes. Operationally, a SPECI has the same format and authority as a METAR, but its unscheduled nature makes it especially critical during volatile weather situations.
Example SPECI: KRFD 011715Z 25015G30KT 210V290 3SM BR BKN015 01/M01 A2984 RMK SLP034
TAF – Terminal Aerodrome Forecast
A TAF is a concise, coded forecast describing the expected weather conditions at an airport over a specified period, typically 24 or 30 hours. Unlike METAR and SPECI, which report current conditions, the TAF supports flight planning and decision-making before departure.
TAFs include forecast wind, visibility, weather phenomena, and cloud coverage, along with time-based change indicators. These indicators describe when weather is expected to become better or worse, temporarily fluctuate, or occur intermittently. Pilots and dispatchers use TAFs to evaluate alternate airport requirements, fuel planning, and overall route feasibility.
Example TAF: TAF EGLL 121100Z 1212/1318 22012KT 9999 SCT025 TEMPO 1214/1218 SHRA BKN015
Flight Rules – Weather Categories Comparison
Flight rules define how aircraft are operated based on visibility and cloud ceiling. The following table summarizes all commonly used flight rule categories.
| Flight Rule | Ceiling (AGL) | Visibility | Operational Description |
|---|---|---|---|
| LIFR (Low Instrument Flight Rules) | Below 500 ft | Less than 1 SM | Extremely poor conditions. Operations rely heavily on instruments and ATC. Often associated with dense fog or very low cloud bases. |
| IFR (Instrument Flight Rules) | 500–1,000 ft | 1–3 SM | Instrument flying required. Common during low ceilings or reduced visibility. |
| MVFR (Marginal Visual Flight Rules) | 1,000–3,000 ft | 3–5 SM | Marginal visual conditions. VFR flight possible but requires increased caution. |
| VFR (Visual Flight Rules) | Above 3,000 ft | Greater than 5 SM | Good weather conditions allowing pilots to navigate primarily by visual reference. |
METAR, SPECI, and TAF – Operational Comparison
While all three products describe airport weather, each serves a distinct operational purpose.
| Product | Type | When Issued | Primary Use |
|---|---|---|---|
| METAR | Observation | Scheduled (usually every 30–60 minutes) | Provides current, observed weather conditions for real-time operations. |
| SPECI | Observation | Unscheduled, as needed | Alerts users immediately to significant or hazardous weather changes. |
| TAF | Forecast | Scheduled (every 6 hours, with amendments) | Supports flight planning by predicting future weather conditions. |
Together, METAR and SPECI offer situational awareness of what is happening now, while the TAF provides insight into what is expected to happen. When combined with flight rule categories, these products enable informed aeronautical decision-making from pre-flight planning through landing.
Explore the airports with the least favorable conditions in the world, split into different categories !