What is Precipitation?

Posted by Robert Dailey Oct 11, 2007

The word precipitation is derived from the Latin praecipitationem, the act of falling from a great height.

In common usage, it means the amount of snow, hail, sleet, rain, dew, or any other type of water that falls from the sky or occurs through atmospheric condensation. It is usually described in inches or in centimeters of water.

However, an inch of snow does not equate to an inch of water. Add to this confusion that temperature also contributes to estimating the amount of water equivalent in snow.

For instance, if the temperature outside is 28 to 34 degrees (F) and snow is falling, in inch of snowsnow is roughly equal to one-tenth of an inch of rain. However, decrease the temperature, to say zero to nine degrees, it would take four inches of snow to equal one-tenth of an inch of rainfall.

In addition, in areas of heavy snowfall, or areas with very low humidity, the real amount of water reaching the ground can be misleading. In very dry areas, much rainfall is lost through evaporation, some before it even hits the ground (this is called virga) and much more just after it hits the ground. In these very dry areas, snow can be transformed to gas without going through melting, in a process called sublimation.

Thus, an area that has officially received a foot of snow when the temperature is -21 degrees (F) only gets one-tenth of an inch of water, assuming that none is lost through sublimation or evaporation.

Related articles include:

1. What is sublimation?
2. What is a Desert?