Lots of Abbreviations But Only One Format

In 1996, with the beginning of airline deregulation, the U.S. started using a new format to disseminate current weather and forecasts. Prior to that time the U.S. (and Canada and Mexico) used Surface Aviation Observations (SAO) for current conditions and Terminal Forecasts (TF), while the rest of the world used METARS and TAFS. METAR is an abbrevaition of the French phrase "message d’observation météorologique régulière pour l’aviation", literally "aviation weather observation". A typical METAR includes the date and time the report was sent (in UTC), the winds, could cover and height above ground, temperature and dew point, and barometric pressure. For example, the METAR for this hour for Pontiac, Michigan is:

KPTK 202349Z 29008KT 3SM -RA BR OVC008 11/09 A3008

The four-letter identifer is an ICAO-format desginator for Oakland-Pontiac Airport. 202349Z is interpreted as the 20th day of the current month at 2349 Zulu (Zulu is slang for UTC 'Universal Time Coordinated' or GMT 'Greenwich Mean Time'). The wind direction is presented followdd by the wind speed; here's it's reported as coming from 290 degrees at 8 knots. The next token is the visibility - here's it's 3 statute miles. RA means rain, but the minus in front mean light rain (and +RA means heavy rain). BR is a token for "mist". The cloud cover is overcast (OVC) at 800 feet above ground level (AGL). The temerature is 11 degrees Celsius, and the dewpoint is 9 degrees Celsius - not much of a spread and perhaps indicative of potential icing conditions. The final token "A3008" is interprested as "Altimieter 30.08 inches of Mercury - the surface pressure reading.

As you can see, reading METARS requires a good understanding of the conventions used to report surface conditions using the METAR format. This format, used all over the world now with only minor changes, as spelled out by exceptions for only a handful of airports, makes it easier for pilots to read the current weather at almost any station in the world.