Gives the geopotential height in meters at the indicated level. The geopotential height differs from geometric height (elevation above sea level) and takes into account the variation of gravity with latitude and elevation.
Layer thickness is a measure of how warm or cold a layer of the atmosphere is, usually a layer in the lowest 5 km (17,000 feet) of the troposphere; high values mean warm air, and low values mean cold air. Rain and snow are equally likely when the 500-1000 hPa thickness is about 5225 gpm (or 522 dam). Rain is rare when the 500-1000 hPa thickness is less than 5190 gpm. Snow is extremely rare when the 500-1000 hPa thickness is greater than 5395 gpm.