METAR (aviation routine weather report) is a format for reporting weather information. A METAR weather report is predominantly used by pilots in fulfillment of a part of a pre-flight weather briefing, and by meteorologists, who use aggregated METAR information to assist in weather forecasting.
METAR reports typically come from airports or permanent weather observation stations. Reports are typically generated once an hour; however, if conditions change significantly, they may be updated in special reports called SPECI's. Some reports are encoded by an automated airport weather station located at airports, military bases and other sites. Some locations still use augmented observations, which are recorded by digital sensors and encoded via software, but are reviewed by certified weather observers or forecasters prior to being transmitted. Observations may also be taken by trained observers or forecasters who manually observe and encode their observations prior to their being transmitted.
The METAR format was introduced 1 January 1968 internationally and has been modified several times since. North American countries continued to use a Surface Aviation Observation (SAO) for current weather conditions until 1 June 1996 when this report was replaced with an approved variant of the METAR agreed upon in a 1989 Geneva agreement. The World Meteorological Organization's publication No. 782 "Aerodrome Reports and Forecasts" contains the base METAR code as adopted by the WMO member countries