A METAR is a weather observation report for aviation, which is routinely prepared every half hour on HH+25 and HH+55 hours for Dutch airports. The measurement data used as information for the METAR come from measuring instruments set up at the various observation areas at the airports. At Schiphol Airport, the METAR is the result of continuous visual monitoring of the weather by an aviation observer and automatic measurements of objective quantities such as wind direction, wind speed, temperature, dew point and air pressure. The on-site observer at Schiphol Airport contributes to the METAR by adding visual observations which include visibility, cloud type, cloud height, cloud cover, and various weather phenomena. At the regional airports of Rotterdam, Groningen, Beek and Lelystad, an automatic METAR report (AUTO METAR) is produced. At those airports, no local airport observers are available.