METAR/TAF
From Pilots Almanac
METARs and TAFs are textually-based weather products. A METAR is an observation of current conditions at a weather reporting station. A TAF is a forecast of conditions within a five-mile radius of an airport.
History
Since the beginning of aviation weather recording, there have been two formats used to report current and forecast weather. North American countries (United States, Canada, and Mexico) used a format referred to as Surface Aviation Observation, or SAO, and the rest of the world, with minor differences, used a format called METAR, to report current weather. The same was true for terminal forecast reports. North American countries used Terminal Forecast, or FT, and everyone else used TAF. As deregulation came to the airline industry; and the number of pilots flying internationally grew, the need to standardize current weather reports and terminal forecast reports became apparent.
For years, discussions took place with the intention of coming to an agreement on one universal format. Finally, a meeting was held in Geneva late in 1989. The product of that meeting was a blend of the existing SAO and METAR reports. Later, terminal forecasts were reviewed. The locally produced FT and international TAF were combined and the new TAF report is the result.
Once the basic formats for METAR and TAF were set, each country was given the opportunity to file for exceptions to the formats to meet the needs of that country. These exceptions had to be approved by the World Meteorological Organization (WMO).
Some of the significant dates in the changeover from SA to METAR, and from FT to TAF are as follows. On January 1, 1996, the NWS converted to the new international METAR format for international dissemination and to the new international TAF format at 90 locations. On February 1, 1996, TAF formatted forecasts issued for an additional 12 U.S. airport locations were instituted. The NWS completely converted to the new METAR/TAF code formats for domestic dissemination beginning at 0800 hours UTC on July 1, 1996 . At that time, SAs and FTs had been replaced with METARs and TAFs and SAs and FTs were discontinued.
U.S. Reporting
On 1 July 1996, the international standard code for hourly and special surface weather observations, METAR/SPECI, took effect. The METAR acronym roughly translates from the French as Aviation Routine Weather Report . A special report, SPECI, is merely a METAR formatted report which is issued on a non-routine basis as dictated by changing meteorological conditions. The SPECI acronym roughly translates as Aviation Selected Special Weather Report . Meanwhile, the international standard code format for terminal forecasts issued for airports, TAF , also took effect. The acronym translates to Aerodrome Forecast .
The Federal Aviation Administration (FAA), which determines aviation requirements in the United States, has determined that the domestic transition to the METAR/TAF code is vital to the standardization of these reports worldwide. The National Weather Service (NWS) and Department of Defense (DOD) are complying with this requirement. The benefits of having the U.S. standardize to these new code formats are as follows. Hourly and special observations are used both as stand alone data for the sites and as inputs to global weather models for both analysis and forecasting. It is this global use of each small bit of information which drives the need for standardization. Additionally, the increase in international flights between the U.S. and other nations from more U.S. locations than ever before lends itself to developing a more "seamless" international standard for aviation. Moreover, standardization becomes vital for the general aviation community for flights from the U.S. to Canada, the Caribbean Area, and Mexico.
The U.S. METAR code is described in Federal Meteorological Handbook (FMH) No. 1 "Surface Observations and Reports", while the U.S. TAF code procedures used by the NWS are described in Weather Service Operations Manual Chapter D-31.
Both of these standards are tailored to reflect existing longstanding U.S. national practices. For example, in order to lessen the burden on the U.S. aviation community, a number of exceptions to metric reporting units have been filed by the U.S. Winds will continue to be reported in knots (as opposed to meters per second), cloud layer heights, and runway visual range (RVR) will continue to be reported in feet (as opposed to meters), visibility will continue to be reported in statute miles (as opposed to meters), and altimeter settings will continue to be reported in inches of mercury (as opposed to hectoPascals). The only element that will be converted to metric units is the temperature/dew point field which will be reported in whole degrees Celsius. In order to allow for a better conversion between Celsius and Fahrenheit, the hourly temperature/dewpoint will be in tenths of degrees Celsius in the additive data remarks section of the METAR report from selected stations in the U.S.
While the METAR code uses some non-English words for some present weather phenomena, the U.S. standard for METAR was developed in a cooperative effort between the NWS, FAA, DOD, and domestic and international aviation industry and organizations. As in any standard developed by a multi-agency group, compromise is essential. Some of the coding groups (e.g., GR for hail or FU for smoke) are based on French words, but many English abbreviations have been adopted. For example, the international abbreviations for Fog and Rain are FG and RA respectively. Essentially, the better aspects of the international and North American codes were merged. See METAR/TAF Abbreviations for more information.
Presenting METARs and TAFs in a plain language format is not feasible. Despite the advances in today's technology, the communication bandwidth used for transmitting the large and diverse suite of meteorological products (radar, upper air, climatological data, forecasts, watches, warnings, outlooks, etc.) is finite. The conversion to a plain language format for thousands of domestic and international observations that are generated each hour of the day is impractical and would easily overwhelm our meteorological communication capability. However, standardization does allow computer programs to easily translate the "code" into plain language.
