Snow Falling But Never Hitting the Ground; Virga
Contributed by Kim Cuozzo, Marketing Associate, Forensic Weather Marketing Team
Sometimes snow shows up on radar but may not actually be falling to the ground. This is known as virga, and can also happen with rain or other types of precipitation. This tends to occur when the layers of air closest to the ground are very dry. The snow falls from higher, moist layers and then evaporates when it reaches the dry air layer. The air isn’t moist enough to support the snow falling all the way to the ground. The reason why it shows up on radar is that the radar beam reflects off of higher layers of the atmosphere rather than the layers closer to the ground, so it detects the snow falling up in the high moist layers. Sometimes you can see virga in the distance – it looks like wisps or shafts of precipitation trailing down from a cloud. So if it looks like it should be snowing in your town according to radar but it’s actually not, then virga is probably occurring high above you!