D.C.'s whirlwind tour through the sweaty jungles of summer is coming to a jarring end. A storm system of bad character is imposing itself on the region tonight. It's already killed people out west, but for us it will likely just make plenty of noise and maybe shake out some hail.
Warm air blowing up from the South will continue to support our thermally acceptable air mass – yesterday, record high minimum temperatures were recorded at both Dulles (67 degrees, above 61 in 1979) and BWI (68 is more than 1990's 66 degrees). The skies will be cloudier today, with chances of isolated thunderstorms in the afternoon. (Latest forecast.) Then, early Thursday morning, a cold front chucked by a Great Lakes low-pressure system is expected to arrive here, summoning the threat of severe weather.
The Storm Prediction Center has given everybody from the Hudson Valley to North Florida a slight risk of major thunderstorms. Even though the cooler early-morning temperatures throw a damper on any storm's potential, the wind profile of this system makes it one to keep an eye on. “There’s a lot of low-level shear,” says ABC7 senior meteorologist Bob Ryan. “It’s possible with that, plus the history of this storm, that it could be severe.”
As for that “history,” the powerful system has dropped hail bombs throughout the South and Midwest – a megahail ball 3.25 inches wide fell on Smith, Texas – and sprayed Arkansas with at least six tornadoes, killing four. Vast flooding has also taken its toll, killing four more. Where's all this angry weather coming from?
“It is a pattern now where there’s a strong temperature contrast in the country,” says Ryan, who notes that while the South is basking in warmth, it snowed in Montana yesterday. “The atmosphere is in transition. The north doesn’t want to quite let go of the cold air, and moisture from the Gulf is coming in. That’s the classic recipe for severe weather.”
The storm should pass by Thursday afternoon, leaving temperatures in the 60s. If the cold front dawdles over the D.C. region, though, there might be flash flooding. That would add to the intensity of the already-turbulent Potomac. Over the weekend, Fletcher's Cove Boathouse was not renting craft because of the river's jacked-up condition. But I know one place that will be safe:
The flood walls are up! Better late than never, right?