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Posted at 11:16 AM ET, 08/10/2012

Risk of severe storms this afternoon and evening in Washington, D.C. and Baltimore

Yellow shaded region is highlighted for slight risk of severe thunderstorms (NOAA)
Morning showers and thunderstorms deposited a quick 0.25-0.75” of rain (Reagan National 0.6”, Dulles 0.53”, and BWI 0.27”). In their wake, pockets of sunshine are emerging from southwest to northeast across the metro region - potentially priming the area for a round of strong and severe thunderstorms late this afternoon and evening.

NOAA’s Storm Prediction Center places much of the mid-Atlantic and Northeast under a slight risk of severe thunderstorms, with damaging wind and hail the primary threats. But - with a bit of spin in the atmosphere (due to turning of the wind with height) - we cannot rule out an isolated tornado.

Left: Jet stream map as of 8 p.m. tonight. Right: Surface weather map as of 8 p.m. tonight. Maps from (left) and NOAA (right), adapted by CWG.
The trigger for the storms is a sizable dip in the jet stream (upper level trough) pushing through the Ohio Valley with a deep pool of cold air. Out ahead of it, warm, moist, and unstable air is surging up the East Coast.

A cold front lies at the intersection of these two contrasting air masses. Along and ahead of this front, showers and thunderstorms are likely to develop this afternoon and evening.

The intensity of the storms will - to some extent - depend on the amount of instability that develops over the region. That’s why the amount of sun we see today is important. More sun means more instability and a greater risk of severe storms. Less sun means less instability and more isolated severe storms.

At the moment, the most likely timing for storms will probably be in the 4-11 p.m. window, although isolated storms could develop prior to that, especially west of the District towards the mountains.

The potential for strong to severe storms, both last night and today, has been apparent since early in the week, as Ian Livingston discussed in some detail in his post Wednesday.


Yesterday evening (Thursday), strong to severe storms rumbled through D.C.’s northern suburbs - producing some isolated hail and damaging wind reports. A number of CWG readers sent in pictures of some of the towering thunderheads as well as hail that were observed. See the images below... allow a few seconds to load...

By  |  11:16 AM ET, 08/10/2012

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