SYNOP (surface synoptic observations) is a numerical code (called FM-12 by WMO) used for reporting weather observations made by staffed and automated weather stations. SYNOP reports are typically sent every six hours by Deutscher Wetterdienst on shortwave and low frequency using RTTY. A report consists of groups of numbers (and slashes where data is not available) describing general weather information, such as the temperature, barometric pressure and visibility at a weather station. It can be decoded by open-source software such as seaTTY, metaf2xml or Fldigi. SYNOP information is collected by more than 7600 manned and unmanned meteorological stations and more than 2500 mobile stations around the world and is used for weather forecasting and climatic statistics. The format of the original messages is abbreviated, some items are coded.

Message format

Following is the general structure of a SYNOP message. The message consists of a sequence of numeric groups, which may also contain slashes (indicating missing data) in addition to numeric digits. Leading numbers are fixed group indicators that indicate the type of observation following, and letters are replaced with numbers giving the weather data. Messages from shipboard weather stations, and in different regions of the world, use variations on this scheme. YYGGiw IIiii iRiXhVV Nddff (00fff) 1snTTT 2snTdTdTd 3PoPoPoPo 4PPPP 5appp 6RRRtR 7wwW1W2 8NhCLCMCH (9GGgg) After this first section, stations may include additional sections, prefixed by (section 2, for manned coastal stations, reporting sea surface temperature and wave data), (section 3, used only in some areas of the world, for the "state of the sky in the tropics"), or (various national code groups).

Example message

This observation was from April 1, 2022, from LaGuardia Airport in New York City. 01124 72503 12566 63015 10106 20050 30003 40016 53048 60071 91151 333 10178 20106 70079 91021 Although this coded data is still available from three American universities it has now been replaced by a universal digital coding system so data can be shared in the same format whatever the source of the observations. This enables Synop, Metar, upperair and satellite data to be processed by a common computer system. The short wave radio transmission of Synop data was common in the 1980s from Bracknell or Paris but this is now redundant. Synop data is available as downloadable files from a number of internet sites including the College of DuPage.

Surface and SYNOP datasets