From the ABC 7 Weather team

D.C. Derecho: Midwest To East Coast Destructive Storms

June 30, 2012 - 04:00 PM
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D.C. Derecho - a name and date we'll all remember.  Millions now try to pick up the pieces after a devastating line of storms plowed through the region.

Before Friday, June 29th, you may have never heard of the term "Derecho".  I'm sure by now, you're well aware of what it means.... and it's probably something you wish you never knew about or had to experience.

A large cluster of thunderstorms developed Friday afternoon on June 29th in Eastern Iowa and continued to intensify, as it marched East into Northern Illinois and Indiana.  A derecho is defined as a long lived wind storm that can travel for hundreds of miles with damage generally following a straight path.  This is where the term "straight line winds" come from.  The powerful thunderstorms travel very fast and as they accelerate, the storms sometimes tend to "bow".  That can result in wind gusts between 60 and 100 mph.  Take a look at a graphic, from the Storm Prediction Center, showing the over 600 mile radius the derecho traveled. 

The strong line of storms approached the D.C. metro area around 10:30 PM.  Many people recount the event, as all of the sudden hearing a loud gust of wind and in many cases, the highest wind gusts occurred before the actual line of heavy rain pushed through.  What was so impressive about Friday night's storms was that they occurred after an afternoon of record breaking heat.  D.C. made it to 104° - breaking the previous record of 101° set back in 1934.  Even after the sunset, temperatures were in the low 90s when the storms plowed through, so there was definitely enough heat energy to support the strong storms, even after they crossed the mountains.  Dewpoint temperatures were also near 70°, so there was a lot of moisture in the atmosphere, as well.  Here's what our Doppler looked like at 10:55 PM, as the line moved through the D.C. metro area.

Doppler at 10:55 PM Friday, June

The line of storms produced wind gusts to 70 mph at both Reagan National and Washington Dulles.  The storms lasted about an hour, but left millions without power and unfortunately a few fatalities.  Take a look at the NWS Storm Reports from Fridays event.  This MidAtlantic view totals 463 reports of wind damage!  There was one confirmed tornado in Newcomerstown, Ohio and even some reports of hail. 

The clean up continues after the devestating storms tore through the Nations Capital Friday night.  Derecho's aren't common in our area, but occur more often in the Southern Plains and Ohio Valley.  The derecho climatology map below puts the D.C. area in a category of one derecho every four years.

SPC Derecho Climatology

Looking back at weather records, D.C. hasn't experienced a significant Derecho event before the Friday occurrence.  Now Western Maryland, parts of Virginia, and West Virginia have dealt with similar weather events, but again, it's nothing that happens frequently.   The "West Virginia Derecho of 1991" originated over Arkansas and traveled Northeast through Tennessee, Kentucky, and eventually moved through West Virigina and extreme Western Maryland.  What I found even more interesting was the "July 4-5 1980 Derecho".  This line of storms traveled almost an exact track to the 2012 D.C. Derecho.  Take a look at the track below:

SPC Track of derecho July 4-5, 1980

Notice how the storm began in Iowa, tracked through Illinois, Indiana, Ohio, and then eventually shifted Southeast through West Virigina and then into Northern Viginia, Maryland, and D.C. 

The 2012 D.C. Derecho will definitely make the record books.  It was unlike something many of us have seen, but will remain infamous in our memories. 

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