What is a derecho? And why might the mid-Atlantic get hit with one?

Intense winds, heavy rainfall, and hail are expected to strike the lower mid-Atlantic states, including Washington, DC, and the central Appalachian Mountains, on Monday evening in what could become a derecho, according to the National Weather Service.

“The risk for damaging winds is expected to continue, and become potentially widespread, through this evening,” NWS reported in its latest alert.

The Washington Post is reporting that the storm is likely to hit DC between 6 and 8 pm, with a severe thunderstorm watch until 9 pm.

Derechos can be devastating storms. The word, Spanish for “straight ahead,” was coined in 1888 by meteorologist Gustavus Hinrichs to distinguish storms producing winds in a straight line from storms that produce rotating winds that cause tornadoes. A derecho storm system is also distinctly wide and fast-moving, causing wind damage for more than 250 miles (larger than the diameter of most hurricanes), with gusts pushing faster than 58 mph along most of its length.

About 70 percent of derechos occur between May and August, and most originate in the central part of the United States when strong, straight winds meet cool downdrafts.


Derecho frequency in the United States

Derecho frequency in the United States.
NOAA

These storms can be dangerous and deadly. A derecho struck the mid-Atlantic region in 2012, killing 13 people and knocking out power to more than a million in the Washington-Baltimore area just as a heat wave struck. Winds gusting up to 80 mph knocked over trees, ripped shingles off roofs, and toppled power poles.


A derecho moving through the mid-Atlantic on June 30, 2012.

A derecho moving through the mid-Atlantic on June 30, 2012.
NASA-GOES

The storm’s rapid formation and swift gallop across the country made it difficult to prepare and caught many people off guard.

And as the climate changes, it’s unlikely that derechos will change in severity, but they may change their range. “There is nothing to suggest that a warmer world necessarily would favor stronger derechos,” according to NOAA. “What can be said with greater certainty about derechos and climate change is that the corridors of maximum derecho frequency likely would shift poleward with time.”

The current storm hasn’t yet reached the threshold of a derecho in terms of size, but forecasters expect it to easily clear the benchmark for wind, with gusts up to 75 mph expected.

It’s best to charge your devices as soon as possible and avoid being outdoors when the storm hits.

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