Severe threat tonight?
A large complex of thunderstorms is taking aim at the Mid-Atlantic and has everyone in D.C. wondering just how concerned we should be about the risk of severe weather here.
The answer is not simple. We should be on alert, but I don't expect a long-lived, widespread, damaging wind event. The Mesoscale Convective System (MCS) developed in the Midwest yesterday. That's a fancy term for a medium-sized cluster of thunderstorms. It produced more than 400 reports of severe weather including tornadoes, winds in excess of 60 mph and very large hail.
Check out the baseball size hail from twitter:
And this semi-trailer in Nebraska was blown over by strong winds.
The MCS has held together for more than 600 miles and is now in the Ohio Valley. Some cities at greatest risk today include Cincinnati, Louisville, Lexington, and Nashville. Notice that much of our area is highlighted in the brown. The Storm Prediction Center has the D.C. region at a 5-percent chance of damaging winds within 25 miles of any point. We are also at 5-percent risk of large hail.
While that threat sounds pretty low, there remains some uncertainty on how this system will behave as it gets close to us. The Stormwatch 7 team is currently predicting that most of the showers and storms will not be severe, but a few could reach dangerous levels. The MCS should weaken as the sun goes down. The mountains can help knock it down a bit, too. In addition, the present forecast track has the low moving right over us, which would bring the stronger storms south of our region.
As for timing, we could see some development of showers and storms this evening, but the main event comes while you are sleeping between 10pm and 7a.m. Expect the early part of the morning commute to be wet, with improving conditions through the morning. Partly sunny skies by the afternoon and a pleasant end to the week. Make sure you watch Good Morning Washington starting at 4:30 a.m. for the latest weather information and how it will affect your drive to work or getting the kids to school.