Measurements Over Land

Measurements made at land stations include temperature, dew point, relative humidity, precipitation, snowfall, snow depth on ground, wind speed, wind direction, cloudiness, visibility, atmospheric pressure, evaporation, soil temperatures, and various types of weather occurrences such as hail, fog, thunder, glaze, etc. In the US, weather observations are normally taken at hourly intervals, but sometimes are taken more frequently under rapidly changing conditions. New and automated weather stations report a more limited list of meteorological variables at 20 minute intervals.

Weather data from the atmosphere above the earth's surface (above about 3 meters) are taken by instrument packages (radiosondes, rawinsondes, and rocketsondes) that are carried aloft by weather balloons that are launched every 12 hours (in the US and many other locations, but less frequently in developing countries) and transmit data to a receiving station on the ground. These "upper air" data include temperature, relative humidity, atmospheric pressure, and wind. Vertical profiles of atmospheric measurements taken at approximately the same time are called atmospheric soundings.

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