Photo: Brian Kahn

Your humble Earther weather correspondent went the roof of Gizmodo Media’s offices to capture the above picture. By the time he descended to the ground floor, all hell had broken loose.

Powerful winds made umbrellas abstract sculptures of plastic, metal, and fabric. And that’s too bad for their owners, as torrential rains turned city streets into rivers as lightning forked across the sky and the National Weather Service New York office urged residents to “SEEK SHELTER NOW inside a sturdy structure and stay away from windows.” Which is why I am holed up in our offices (far from windows of course!) writing this blog instead of heading home.

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So, what the hell happened on a day that started sunny and stayed that way until 15 minutes before the gates of hell appeared over Midtown? If you’re a Twitter user, you’ve probably seen the term derecho thrown around today, as well as on Monday when the Washington, D.C. region was buffeted by powerful storms and the president drove through an area under a freaking tornado warning (pro tip: do not do this even if you’re leader of the free world).

A derecho is basically a powerful windstorm that moves in a straight line unlike tornadoes, which spin in a tight area, or hurricanes, which spin over a much larger area. Making things even more confusing: some derechos can come with tornadoes.

So, was this a derecho? Well, it’s complicated.

The pattern of wild weather began this morning. Those same sunny skies helped heat the land up, while winds from the south drew even more hot, humid air into the region. Temperatures peaked in the upper 80s in New York and 90s further south. A cap of stable air in the atmosphere allowed all that heat to build up, a setup that Capital Weather Gang wrote this morning would help “rapidly destabilize the atmosphere this afternoon.”

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We saw that start in central Pennsylvania, where the powerful series of thunderstorms built into the afternoon before lumbering toward the I-95 corridor. Along the way, they dropped hail the size of baseballs and left a wake of lightning that looks like an open wound across Pennsylvania.

The storms then plowed into New York right at rush hour. I didn’t have an anemometer on the roof of Gizmodo Media HQ, but I feel safe saying it was windy as fuck. Video showed gusts swirling water out of a rooftop pool. And wind gusts have already hit 40 mph in Massachusetts, which is next in line to get hammered. Forecasts indicate winds could top out at 70 mph in some locations.

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So yes, storm bad. But derecho bad? According to the Storm Prediction Center, “by the present definition, derecho winds must meet the National Weather Service criterion for severe wind gusts (greater than 57 mph) at most points along the storm path.” They also have to widespread.

So far, at least, this storm hasn’t met the official derecho criteria. But you should still exercise extreme caution, avoid driving on flooded roadways, and stay away from rooftops and other areas that could expose you to lightning.

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