A METAR (Meteorological Aerodrome Report) is a standardized weather observation report issued at airports worldwide, typically every hour. It provides current surface conditions including wind, visibility, cloud cover, temperature, dew point, and altimeter setting. Pilots are required to review METARs as part of preflight planning.

A TAF (Terminal Aerodrome Forecast) is an aviation weather forecast valid for the area within 5 statute miles of an airport. TAFs are usually valid for 24–30 hours and are updated every 6 hours. They use the same encoding as METARs with additional change indicators (FM, TEMPO, BECMG, PROB) to describe expected weather evolution.

Routine METARs are typically issued once per hour, usually around 55 minutes past the hour. When weather conditions change significantly between scheduled observations, a special report (SPECI) is issued immediately.

A SPECI is a special (unscheduled) METAR issued when significant weather changes occur between routine observations — such as a rapid change in visibility, ceiling, wind, or the onset of thunderstorms or freezing precipitation.

AUTO indicates the observation was generated by an automated weather station without human augmentation. Automated stations may have limitations — for example, they may not accurately report thunderstorms, volcanic ash, or certain types of precipitation.

AO1 indicates an automated station without a precipitation discriminator (cannot distinguish between rain and snow). AO2 indicates an automated station with a precipitation discriminator. Most major airport stations in the United States are AO2.

VRB (Variable) in the wind group means the wind direction is varying and cannot be assigned a single predominant direction. This typically occurs with light winds (usually 6 knots or less).

P6SM means visibility is greater than 6 statute miles. The "P" prefix stands for "plus" or "more than." This is the maximum visibility reported in a standard U.S. METAR.

CAVOK (Ceiling and Visibility OK) is used internationally (not in U.S. METARs) when visibility is 10 km or greater, there are no clouds below 5,000 feet or the minimum sector altitude (whichever is higher), no cumulonimbus at any altitude, and no significant weather.

A ceiling is the lowest layer of clouds reported as Broken (BKN, 5/8–7/8 coverage), Overcast (OVC, 8/8 coverage), or obscuration with Vertical Visibility (VV). Few (FEW) and Scattered (SCT) layers do not constitute a ceiling.

BKN stands for Broken and indicates cloud coverage of 5/8 to 7/8 of the sky. A BKN layer is the minimum coverage that constitutes a ceiling. It is reported with a height in hundreds of feet above ground level (e.g., BKN080 = broken clouds at 8,000 feet AGL).

VV (Vertical Visibility) is reported when the sky is obscured (e.g., by fog, heavy snow, or smoke) and individual cloud layers cannot be identified. The value gives the vertical distance a pilot can see upward, in hundreds of feet (e.g., VV005 = vertical visibility 500 feet). VV counts as a ceiling.

RVR (Runway Visual Range) is the distance a pilot can see down a specific runway, measured by transmissometers near the runway. RVR is reported in feet (U.S.) or meters (internationally) and is included in a METAR when visibility drops below certain thresholds. It is critical for determining whether instrument approach minimums are met.

TEMPO indicates temporary fluctuations from the prevailing conditions that are expected to last less than one hour at a time and occur during less than half of the specified time period. For example, TEMPO 1812/1815 +TSRA means heavy thunderstorms with rain are expected temporarily between 12Z and 15Z on the 18th.

FM (From) indicates a rapid, significant, and sustained change in prevailing conditions. Conditions after the FM group completely replace the previous forecast. For example, FM181500 means a new set of conditions begins at 15:00 UTC on the 18th.

PROB30 indicates a 30% probability of the specified conditions occurring during the given time period. PROB40 indicates a 40% probability. These are used in TAFs when conditions are possible but not expected to be the prevailing weather.

IFR (Instrument Flight Rules) applies when the ceiling is 500–999 feet AGL or visibility is 1–less than 3 statute miles. LIFR (Low IFR) applies when the ceiling is below 500 feet or visibility is below 1 SM. LIFR conditions are more restrictive and may be below the minimums for many instrument approaches.

No. MetarDecoder is an educational tool designed to help pilots understand weather reports. It is not a substitute for an official preflight weather briefing from an approved source such as 1800wxbrief.com (Leidos Flight Service) or aviationweather.gov. A complete weather briefing includes additional products such as AIRMETs, SIGMETs, PIREPs, winds aloft, convective outlooks, and NOTAMs that are not available here.

Weather conditions can vary significantly over short distances due to terrain, elevation differences, proximity to water, urban heat effects, and localized weather phenomena. A METAR reports conditions at one specific point (the weather station at the airport), which may not represent conditions even a few miles away. Always check weather at departure, destination, and alternate airports independently.