What exactly is a ‘derecho’?

WASHINGTON – So you keep hearing about it, but what exactly is this thing called a “derecho”?

By definition, a derecho is a storm of strong straight-line winds spanning at least 240 miles. A derecho’s rare, explosive wind pattern is comparable to the landfall of a hurricane.

“Derechos are huge windmakers. They can transport a tremendous amount of downward momentum to the surface,” says WTOP traffic reporter and storm chaser Dave Dildine.

Some have said Thursday’s weather conditions are ripe for this type of storm, which struck the D.C. area, and the country, just one year ago.

Last June’s derecho was considered a progressive derecho. Dildine explains that progressive derechos form when extremely hot air moves up from the south and clashes with cooler air in the north.

These storms can pack a dangerous punch. Last year’s caused at least $1 billion in damage from Chicago to Washington, killing 13 people and leaving more than 4 million people without power.

In the D.C. area, hundreds of thousands of people were left without power.

“Thursday’s setup does favor the potential of a progressive derecho, and that is of utmost concern,” Dildine says.

Related articles:

  • Comparing Washington’s recent derechos
  • Storms hammer D.C. area after record-setting heat
  • Timeline of derecho that hit Friday

    WTOP’s Joan Jones and The Associated Press contributed to this report. Follow @WTOP on Twitter.

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