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Garrett’s Blog: Those Weird Clouds This Morning

On your way into work this morning you may have noticed some strange clouds in the sky. They look like normal clouds only their base is smeared down forming som...

On your way into work this morning you may have noticed some strange clouds in the sky. They look like normal clouds only their base is smeared down forming something that looks like a Jellyfish.

The streaks you were seeing under the  clouds are known as “Virga” and occur from precipitation either evaporating or sublimating as it falls to the ground.

 

The word “virga”: is Latin for ‘rod’or ‘trig’. It develops when there’s enough lift in the atmosphere to cause a cloud to reach 100% saturation where rain develops.

The clouds are usually high based and then rain then falls into a layer of the atmosphere that is very dry and evaporation takes place leaving these streaks of clouds.

Virga over Bentonville, Arkansas. Photo: Chris-Mary Finley.

There are probably times when you see rain over your house on doppler radar but step outside and nothing’s falling from the sky. The radar beam may be reaching into the part of the cloud where it is actually raining but down at the ground the air may be too dry so the drops evaporate.

Virga is most common in arid climates like deserts but occasionally happens in our area when the low levels are dry enough; that’s usually the winter months for our area when moisture above our heads is greater than the cold dry air that resides as the surface.

When virga falls it’s moistening up the lower levels of the atmosphere and also cooling the atmosphere, too. This is important for us to forecast wintry precipitation type because often the dry air at the surface can become saturated and also much cooler which usually leads to the changeover from rain to snow; that’s part of another meteorological process known as ‘wet-bulb cooling’.

-Garrett

 

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