Observation stations within the Land SYNOP station network transmit their observations, made on land, in the form of a SYNOP message. The international SYNOP message format has been used for the real time transmission of synoptic weather observations for about 50 years. Today it is used at some 200 or more Met Office or auxiliary UK stations for observations made at hourly, 3-hourly, 6-hourly or irregular intervals. As well as the UK station, there are thousands of SYNOP stations distributed globally resulting in around 60,000 reports a day. Data are extracted for the 4 principal synoptic periods (00-06, 06-12, 12-18 and 18-00 UT) from the Met Office's MetDB system and delivered to CEDA at 13:30, 19:30, 01:30, and 07:30 respectively (all in GMT). The SYNOP message contains observed elements such as weather, cloud, temperature, humidity, wind, visibility, and pressure.

In order for a SYNOP message to be transmitted by an observation station, specific instruments are required to perform to certain standards. These include an anemometer, thermometer, station observer, sunshine recorder, visiometer, barometer, hygrometer, and raingauge. SYNOP messages are typically sent every six hours on shortwave using radioteletype (RTTY) and consist of groups of numbers (and slashes where data are not available). The message is decoded and the relevant parameters are stored in the MIDAS dataset and in the MetDB systems at the Met Office.