Weird clouds spotted over Northern Illinois

Many of you spotted these weird clouds overhead on Monday. Earlier this evening, I posted one on Facebook and asked if anybody wanted to guess what was going on. Michael Janssen said “Snowing but not reaching the ground.” Joseph Girouard said “Flock of Altocumulus with virga.” You both are exactly correct!

UntitledLet’s examine Lorraine Dyba’s photo from Dixon, Illinois. Here you can see a few cumulus trying as hard as they can to develop. Unfortunately, there isn’t much moisture in the air. And there isn’t enough instability to keep them going. Notice the lack of a discernible updraft. For rising motion, look for hard edges on the top of the clouds. (Think about the cauliflower appearance to Summer cumulus clouds.) Instead, what’s going on here are cumulus clouds that are literally falling…quite literally! Looking closely, you can see some precipitation falling out of the clouds. Instead of a rain or snow shaft falling all the way to the ground, the precipitation is falling into dry air. This is called virga. So if you were under the clouds, you’d stay dry, even though the clouds above you were producing rain and/or snow.

Cool stuff!

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Posted under weather geek

This post was written by qni_it on March 19, 2014

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