Land-based observations are collected from instruments sited at locations on every continent. They include temperature, dew point, relative humidity, precipitation, wind speed and direction, visibility, atmospheric pressure, and types of weather occurrences such as hail, fog, and thunder. The bulk of these observations are carried out by National Meteorological Services as part of the WMO World Weather Watch, which networks the observing stations to national, regional and global weather and climate prediction centres 24 hours a day in real-time.
The World Weather Watch collects meteorological, climatological, hydrological and oceanographic data from over 15 satellites, 100 moored buoys, 600 drifting buoys, 3 000 aircraft, 7 300 ships and some 10 000 land-based observation stations. This data has to be comparable and up to standards in order to be usable by the prediction centres in the numerical weather prediction models that produce daily weather forecasts and early warnings for natural hazards such as hurricanes. Thus, the World Weather Watch also produces the standards for measurement of the data collected.
Further reading: Reanalyses and Observations: What’s the Difference?
