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07/18/2012

CRAZY CLOUDS: The Thunderstorm Anvil

The thunderstorm anvil is a common sight during the summer months here in Kentuckiana.  

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Anvil clouds, which are mostly comprised of ice particles, form in the upper parts of thunderstorms or cumulonimbus clouds.  

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They get their anvil shape from the fact that the rising air in thunderstorms expands and spreads out as the air bumps up against the bottom of the stratosphere.  This is because the air in the stratosphere is warmer than the rising air in the anvil, and so prevents the relatively cooler anvil air from rising any farther. 

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You can often seem them even when they are many, many miles away.  This is because the anvil, located at the top of the thunderstorm, can reach altitudes of more than 10 miles high.   In some cases, these thunderstorm tops can be seen more than 100 miles away!  

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You will often see streaks of snow called "virga" falling out of the edges of anvils. This virga evaporates as it falls through the relatively dry air surrounding the upper part of the thunderstorm. 

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The anvil cloud gets it's name from it's resemblance to the tool often used by metal workers.

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This is what a thundestorm anvil looks like from space.  

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Notice the area of clouds that seems to be "bubbling up" right of the center of the one pictured here.  That is known as an "overshooting top" and is a sign of a strengthening storm.  

Another feature of the anvil, is lightning.  While lightning is most common in the lower half of a thundestorm, lightning that originates from the anvil is the most dangerous.  

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Sometimes referred to as a "blolt from the blue", lightning that originates from the anvil, is characterized by a positive charge and can be 10 times more powerful than ordinary lightning.  

They can also strike as much as 30 miles away from the storm, which is where the name "bolt from the blue" comes from.  Even though the sky may be blue above you, if a thundestorm is whithin 30 miles, a positive lightning strike is possible!

Here's are a couple cool time lapse videos of thundestorm anvils...

 

 

 

If you have an idea for a CRAZY CLOUDS topic, you can email me at jkappell@wdrb.com.

Meteorologist Jeremy Kappell

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wow crazy clouds indeed

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