Virga. You have probably heard us use the term multiple times on air, but what is it? Virga, not to be confused with Virgo, is water or ice particles that evaporate before reaching the ground as precipitation. It comes from the latin word for “twig” or “branch”.
Virga looks like tendrils or tentacles hanging from the base of the cloud. This is because the precipitation falling is evaporating into the atmosphere before it reaches the ground. This makes it look like the cloud has tentacles. The appearance of the phenomenon gives it the nickname of jellyfish clouds.
Formation of Virga
Virga occurs typically with the presence of upper level lift moving into the area. This can come from a shortwave trough or a jet streak. The issue is the lack of moisture in the lower levels.
We had a cold front push through Tuesday. This dried out the lower levels of the atmosphere due to the cooler, drier air mass that was ushered in behind the front. Wednesday morning we had a shortwave trough move into the area bringing a wave of precipitation with it. The mid levels of the atmosphere were saturated, but the low levels were very dry.
The dry air at the surface ate away the precipitation for the most part as it fell from the clouds. This greatly limited the amount of measurable precipitation we received.
The Danger of Virga to Aviation
Virga may look beautiful, but it can create dangerous weather especially for aircraft. As the precipitation evaporates, the surrounding atmosphere cools. This cooling happens because the precipitation particles need to absorb heat in order change from water to water vapor.
With all of the evaporating precipitation, the atmosphere rapidly cools creating a layer of cool dense air. This dense layer of air then rushes towards the ground and spreads out. We call this a dry microburst.
Dry microbursts can be even more dangerous than wet microbursts because they are not clearly visible. There are no rain foots for pilots to visually see indicating that they might be flying into a microburst. They will just encounter a sudden loss of lift, which could be fatal. Microbursts are extremely dangerous to aircraft operations.
Send Us Your Photos!
If you are ever outside and are able to capture virga in action, send us a photo to email@example.com. You might just see your photo end up on air.