How to Decode & Read a METAR and TAF

By Walter Zapotoczny
airplane image by Tammy Mobley from <a href='http://www.fotolia.com'>Fotolia.com</a>

Weather affects a pilot's flying activity more than any other physical factor. There are two main reports that pilots use to determine weather conditions: Meteorological Aviation Routine, or METAR, and Terminal Aerodrome Forecast, or TAP. Selected Special Weather Report, or SPECI, is the code name given to a METAR report that is issued on a special basis. METAR observations are reported every hour. TAF reports are issued four times a day: 0000Z, 0600Z, 1200Z and 1800Z. METAR is the current weather conditions. A TAF is a forecast. METAR and TAF reports always appear in a line sequence from left to right.

METAR

Step 1

Type of reports: METAR or SPECI. (Cumulative example: METAR.)

Step 2

Station Identifier. METAR uses standard four-letter International Civil Aviation Organization, or ICAO, location identifiers. For the continental United States, three letter locations are prefixed with a "K." Elsewhere in the world, the first one or two letters of the ICAO identifier indicate the region, state or country of the station. A complete worldwide listing is contained in ICAO Document 7910 "Location Indicators." (Cumulative example: METAR KEWR.)

Step 3

Date and time of report. The date and time is reported as a six-digit date/time group, followed by a "Z" to denote UTC (Coordinated Universal Time), often referred to as ZULU. (Cumulative example: METAR KEWR 142355Z.)

Step 4

Report modifier, if required. Two report modifiers may appear after the date/time group. AUTO indicates the report comes from an automated weather observation station without augmentation or backup. The absence of AUTO discloses that the report was produced manually. COR means the METAR or SPECI report was originally transmitted with an error that has now been corrected. (Cumulative example: METAR KEWR 142355Z AUTO.)

Step 5

Wind. Wind direction is always reported in relations to true north, given as the direction from which the wind is blowing and to the nearest 10 degrees. The first three digits indicate wind direction. The next two or three digits indicate speed. The units of measurement follow (KT) knots, kilometers per hour. Gusts (G) refer to rapid fluctuations in speed that vary by 10 knots or more. (Cumulative example: METAR KEWR 142355Z AUTO 18G24KT.)

Step 6

Visibility. Visibility is a measure of the transparency of the atmosphere. Visibility from manual observations is reported as prevailing, in statute miles "SM." (Cumulative example: METAR KEWR 142355Z AUTO 18G24KT 15SM.)

Step 7

Weather and obstructions to visibility. Precipitation and obstructions to vision may contain some or all of the following elements: Intensity, Proximity, Descriptor, Precipitation or Obstructions to vision. In this example, + TSRAGR is a thunderstorm with heavy rain and hail (The letter "M" means minus or less than; the letter "P" means plus or more than). (Cumulative example: METAR KEWR 142355Z AUTO 18G24KT 15SM PTSRAGR.)

Step 8

Sky conditions. METAR sky condition consists of the amount of sky cover, height in feet, and under certain conditions, cloud type. Cloud heights are reported as three digits, in hundreds of feet AGL (above ground level), following sky condition (SCT030, 3000 scattered). (Cumulative example: METAR KEWR 142355Z AUTO 18G24KT 15SM PTSRAGR SCT030.)

Step 9

Temperature and dew point. These are reported using two digits in whole degrees Celsius, separated by a solidus (/). (Cumulative example: METAR KEWR 142355Z AUTO 18G24KT 15SM PTSRAGR SCT030 20/15.)

Step 10

Altimeter setting. The altimeter, in inches of mercury, follows temperature/dew point in a four-digit group prefixed with the letter "A." (Cumulative example: METAR KEWR 142355Z AUTO 18G24KT 15SM PTSRAGR SCT030 20/15 A2992.)

Step 11

Remarks. Remarks are divided into automated, manual and plain language, and additive and automated maintenance date. Any remarks follow the contraction "RMK." Frequent lightning, cloud to cloud, near the station, southeast would be RMK FRQ LTGCC VC SE. (Cumulative example: METAR KEWR 142355Z AUTO 18G24KT 15SM PTSRAGR SCT030 20/15 A2992 RMK FRQ LTGCC VC SE.)

TAF

Step 1

Type. A routine forecast is TAF. An amended forecast is AMD. (Cumulative example: TAF.)

Step 2

Location. TAF uses the same standard four-letter International ICAO (Civil Aviation Organization) location identifiers as METAR. (Cumulative example: TAF KEWR.)

Step 3

Issuance time. Issuance date and time consists of the same six-digit group format used in the METAR report. The first two digits represent the day of the month and the last four digits UTC issuance time. (Cumulative example: TAF KEWR 142355Z.)

Step 4

Valid time. The valid period is a four-digit group, usually 24 hours, in UTC. (Cumulative example: TAF KEWR 142355Z 2355.)

Step 5

Forecast. The forecast group is divided into body and remarks. Remarks amplify or describe conditions that differ from that in the body of the forecast group. Conditional terms describe variability. In the United States, TAF covers a 5-statute mile radius of the center of an airport's runway complex. Like the METAR code, wind is forecast as a five or six digit group when considered significant to aviation. In the example: WS = wind shear, 015 = height in hundreds of feet AGL of the wind shear (1500 ft AGL), /24035 = wind direction and speed (knots) above the wind shear (240 degrees at 35 knots). (Cumulative example: TAF KEWR 142355Z 2355 WS015/24035KT.)

About the Author

A former U.S. Army historian, Walter Zapotoczny has been writing since 1990. His articles have appeared in “World War II History” magazine and the “World Book Encyclopedia.” Zapotoczny received the Military Writers Society of America's 2010 Bronze Medal for historical fiction. He holds a Master of Arts in history from American Military University.