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Why every severe storm isn't a Derecho

Published On: Jun 04 2014 10:51:23 AM EDT
Updated On: Jun 12 2014 12:03:54 PM EDT
Derecho Criteria

Not every storms is a Derecho.  Here's a look at what makes a storm complex a Derecho.

The word "Derecho" is used a lot these days. We wanted to ease your mind that night every cluster of storms we forecast becomes a Derecho. Just like every snowstorm in the winter doesn't mean it's going to be the "big one!"

After the Mid Atlantic's Derecho on June 29, 2012, the word brings a flashback of the destruction we experienced.

In simplest terms, a Derecho is a long-lived complex of storms that produce extensive wind damage. However, not all clusters of storms become a Derecho. The Storm Prediction Center has a specific set of criteria that is used.

  • A Derecho is a long-lived wind storm, often lasting longer than 6 hours
  • Storms extend continuously for a least 240 miles.
  • Wind gusts 58 MPH or higher along the entire span of storms

Derechos can carry hurricane or tornadic winds and can also deliver heavy rains and flash flooding.  During the June 2012 derecho, winds topped 80mph as they moved through southwest Virginia.

On radar, the line of storms often takes on backward "C" shape, called a bow echo. The front of the "C" points to the area that may be experiencing the strongest winds.  In a true Derecho, that bowing line of storms must stretch more than 240 miles.

WHAT CAN WE EXPECT LOCALLY?

Wednesday Evening (June 4th) First off, we are NOT expecting a Derecho in southwest Virginia this evening. We can't rule out scattered showers and storms. Any wind damage would be confined to isolated stronger cells, NOT a widespread wind event.

The main severe risk will be from far Southwest Virginia into Kentucky and Tennessee.