'Derecho' storm wasn't first to strike Md.

By Scott Dance

1:55 PM EDT, July 2, 2012


The storm that devastated much of Maryland on Friday, known as a "derecho", not the first of its kind to strike the state, but its impact was among the most severe and widespread.

Derechos are widespread storms in which multiple bands of strong storms packing damaging winds move hundreds of miles. According to the National Weather Service Storm Prediction Center, their name comes from the Spanish word for "direct" or "straight ahead", which is the way the storms typically move.

The heavy winds, typically upward of 60 mph, come from downbursts in storm clouds, caused by differences in the heat and density of air within the storm systems.

Most of the storms occur between April and August in the southern Plains or Mississippi and Ohio valleys, but they have been known to reach the mid-Atlantic and even New England. They happen, on average, once every two to four years in Maryland.

A derecho with the intensity of Friday's storms happens in the mid-Atlantic once every five to seven years, said Greg Carbin, warning coordination meteorologist for the storm center in Norman, Okla. But systems with, say, half of its intensity pass through every summer, Carbin said.

Here are some notable past derechos that reached Maryland, according to the storm center:

There is already an extensive Wikipedia page for Friday's derecho; check it out here.

Have a weather question? E-mail me at sdance@baltsun.com or tweet to @MdWeather.