Last year I developed a list of Ten Unique Ideas, Facts and Uses for XML. I just recently realized another one that impacts all of us every day. METAR is the most popular format in the world for the transmission of weather data.
It is highly standardized through International Civil Aviation Organization (ICAO), which allows it to be understood throughout most of the world. The name METAR has its origins in the French phrase "message d’observation météorologique pour l’aviation régulière" ("Meteorological observation message for routine aviation") and would therefore be a contraction of MÉTéorologique Aviation Régulière. 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. Although the general format of METAR reports is a global standard, the specific fields used within that format vary somewhat between general international usage and usage within North America. Note that there may be minor differences between countries using the international codes as there are between those using the North American conventions.
Two file formats are provided: RSS and XML. Weather observations formatted with xml tags aid in the parsing of the information by automated programs used to populate databases, display information on webpages and other similar applications. XML feeds offer URLs to icon images. Much of a METAR is coded; for example: Peak Wind is (PK_WND), Wind Shift (WSHFT_time) and BINOVC (Breaks in Overcast). Another interesting code is: KORD-Station ID. In this example, K refers to a US Station and ORD is the three letter id for O' Hare (from Orchard Field, its original name). Volcanic eruptions are in plain English.
Now the good news. All this data is free. It is all available by anonymous FTP at http://weather.noaa.gov/weather/metar.shtml.