Thunderstorms come and go and rarely leave such a lasting mark on a region, let alone a vast swath of the eastern portion of the country.

So what caused Saturday’s storm system that generated so much damage and lasted so long?

It was a rare type of thunderstorm system called a derecho, which is a “super organized group of thunderstorms,” said Gary Szatkowski, meteorologist with the National Weather Service in Mt. Holly.

Rather than following the typical pattern of storms that beef up during the afternoon and die down as soon as the sun sets, this type of storm fuels itself. “We tend to see them when there’s really hot and humid weather conditions like we had (Friday),” Szatkowski said.

The cold air at the top of the storm causes the hot air at the bottom to rise and, in effect, rolls across the land causing very high straight-line winds, rain and hail. Tornados are rare in this type of system, but the straight-line winds can produce an extreme level of damage.

Saturday’s derecho stretched from Central Pennsylvania southward nearly to the North Carolina border and traveled from just east of Chicago, where it formed around lunchtime Friday.

Meteorologists will see a derecho of a similar magnitude somewhere in the country about every three to five years, Szatkowski said. But for non-weather watchers, “this will be one of the worst ones you will experience in your lifetime.”

At the storm’s peak, winds gusted more than 80 miles per hour, with sustained winds of between 50 mph and 60 mph lasting about 30 minutes. Most thunderstorms with intense straight-line winds only last a few minutes.

Szatkowski said he thought it would be unlikely for another round of intense storms to hit South Jersey Saturday because the atmosphere still is recovering from the intense energy that was released.

And while the clean-up begins in South Jersey and other places that were hit hard by the storm, meteorologists are starting the process of studying exactly what happened to better understand a relatively rare weather system.

“I think this will be something that meteorologists and scientists will study,” Szatkowski said.

Contact Sarah Watson:


Follow Sarah Watson on Twitter @acpresssarah

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