"Derecho" winds not expected to reach Baltimore

Steve Zubrick, the science officer at the National Weather Service's forecast office in Sterling, Va., doesn't think the "derecho" winds that have caused damage in a swath across the Upper Midwest today will remain intact by the time they reach Maryland overnight tonight.

But lots of people are watching this unusual storm pattern, which has reportedly produced winds up to 85 mph and hundreds of reports of wind damage from Iowa to Ohio. More than 800,000 customers lost power in the Chicago area as a result of the storms.

Derechos occur when large clusters of thunderstorms produce a broad pattern of high-speed, straight-line winds along a curved front, called a "bow echo" because of their appearance on weather radar. Wind speeds can exceed 50 mph and sometimes reach hurricane force. The wind front can be tens of miles wide and continue for hundreds of miles.

Asked about Monday's storms, Zubrick said, "I'd call this more of an MCV [a mesoscale convective vortex] ...although technically it's pretty close to being a derecho ... Yes...we do get derechos here, but typically we don't. I'm pretty sure this line of storms ... is going weaken as it moves east after passing Western MD. We'll see."

Severe Thunderstorm Watches are posted for Allegany and Washington counties before 11 p.m. tonight. Large hail, damaging winds and heavy rain are possible, with up to three-quarters of an inch of rain.

The forecast for Central Maryland calls for a 30 percent chance of showers and thunderstorms after 3 a.m. Less than a tenth of an inch of rain is expected, with more in thunderstorms.

UPDATE, 7 p.m.: The NWS has issued a Severe Thunderstorm Watch until 11 p.m. for all of Maryland west of the Chesapeake Bay. Large hail, damaging winds and heavy rain are possible, along with as much as three-quarters of an inch of rain. Maybe this thing will make it to Baltimore after all.

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