Precipitable Water

Precipitable water (total column water vapor) is the depth of liquid water that would result if all the water vapor in a vertical atmospheric column condensed and fell, in millimeters or kg/m2 (numerically equal). It measures the moisture available for precipitation and is a strong absorber of longwave radiation, so it shapes the surface radiation budget. Marine values range from a few millimeters in cold dry air to over 60 millimeters in the tropical warm pool. Radiosondes, GPS delay, and passive microwave radiometers measure it; it links the latent heat flux that supplies evaporation to the column moisture that feeds rain.