The Washington Post

Stop focusing on whether it’s a derecho or not: it’s a serious storm risk

A complex of violent thunderstorms, some tornadic, may or may not coalesce into a derecho sometime this afternoon or evening in the Midwest.  This derecho may affect parts of the Ohio Valley but will probably die overnight before reaching the Mid-Atlantic Thursday morning.

Irrespective of the fate of any derecho, we’ve got our own problems  – as I outlined in my earlier post:

1) Clusters of strong storms born this afternoon in the Ohio Valley (not a derecho), capable of producing damaging winds and flooding rain, may smack us in the middle of the night (50 percent chance).

2) A line of storms, developing along an unusually potent June cold front, may deliver a second round of flooding rain and damaging winds during the day Thursday, as well as the chance of some tornadoes.

The derecho talk has become a huge distraction.

As I said in my post Monday,  a storm complex must meet strict criteria to be considered a derecho: it must be 240 miles long, move at high speeds, and have damaging 58 mph or stronger winds throughout that line.  Our region experiences a derecho just once every four years on average.

A derecho is notoriously difficult to predict, and you can’t really reliably warn of one until it’s in the process of forming or already formed.

Further, let me stress, you can get derecho-like impacts from non-derecho storms.

Although I don’t think the storm system coming through tonight and Thursday will have the same impact as the derecho of June 29, 2012 –  a truly exceptional event, it certainly has potential to create widespread hazardous weather conditions and be the most severe weather event this year to date.

For now, rather than worrying about whether a derecho is going to happen, focus on the potential impacts of the storms that may affect us. In the case of tonight and tomorrow, they’re dangerous.

Jason is the Washington Post’s weather editor and Capital Weather Gang's chief meteorologist. He earned a master's degree in atmospheric science, and spent 10 years as a climate change science analyst for the U.S. government. He holds the Digital Seal of Approval from the National Weather Association.
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Jason Samenow · June 12, 2013

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