Weather Facts



What is Virga?

Virga is precipitation that evaporates before it hits the surface of the earth. Virga is actually very common and can occur at any time of the year. Normally, it is a result of a dry lower atmosphere. Initially, when precipitation begins to fall from the thickening clouds as a low pressure area approaches, the light precipitation will evaporate as it falls to the earth. This process does two things. It moistens up the lower atmosphere and it cools the lower atmosphere from evaporational cooling. As the low pressure area (or warm front) move closer and the precipitation gets heavier, it eventually reaches the ground. Sometimes you could actually see virga. On certain days, when there is a lot of vertical instability in the atmosphere, you will have large cumulus and cumulonimbus clouds that can produce precipitation but it never hits the ground. And due to the normally good visibilities on days like that, you could actually see the precipitation under the base of the clouds against the blue sky in the background and then it fades away as it falls to the ground. The precipitation will appear like a veil of gray hanging from the cloud.

Dave