Get a snow alert and no snow? It's virga, but what is virga?
Jan 08, 2025
Did you get a weather alert saying it was snowing?
Technically, snow was falling, but it wasn’t visible from the ground. This weather phenomenon is called virga. If you’ve ever noticed tiny streaks beneath a cloud, it might be a sign you’re observing virga.
Virga occurs when rain or snow falls from a cloud, but the droplets evaporate before reaching the surface. This happens because the air below the cloud is too dry to support growth, allowing precipitation to hit the ground.
This is exactly what happened here. The strong, northerly winds brought very cold air with dew points in the teens, making the air extremely dry. Wind shifts play a crucial role in determining whether the air contains moisture. Winds from the south, however, bring higher dew points, signaling more moisture in the air.
One way to identify virga is to look for clutter or splatter on the radar. When surface temperatures are below freezing, this clutter, which would normally appear green on the radar, may appear blue, like in the picture below.
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