METAR OBSERVATION CODE

GENERAL

In the World Meteorological Organization method of numbering code forms, each code form bears a number preceded by the letters FM. This number is followed by a Roman numeral to identify the session of CSM (Commission for Synoptic Meteorology) or of CBS (Commission for Basic Systems) which either approved the code form as a new one or made the latest amendment to its previous version. A code form approved or amended by correspondence after a session of CSM/CBS receives the number of that session.

An indicator term is used to designate the code form colloquially and is therefore called a "code name." In some cases, this code name is included as a symbolic prefix in the code form and during transmission ensures ready identification of the type of report.

The METAR code (FM 15-IX) is the international code to report routine, hourly weather conditions at air terminals. SPECI (FM 16-IX) is the name of the code for an aviation selected special weather report.

The METAR code is a precise, easy to read code which provides a great deal of information. The code format is also used by most of the world to provide pilots with trend forecast weather at air terminals to which they are flying. This code has been adopted as the international code for reporting weather conditions by all nations.

On 1 July, 1996, the United States converted to the METAR format. The United States has filed with WMO certain exceptions to the international METAR format that reflect national observing practices which differ from practices outlined in the WMO Manual on Codes No. 306. These exceptions are identified in the discussion of the separate sections of the METAR code.