Update 4:13pm: The potential for severe weather is over for the D.C. area as the instability has been robbed from the showers and storms that crossed ahead of the front. An isolated storm will be possible the remainder of the evening as the remnants of the line pushes south. Much stronger showers and thunderstorms exists through the western portion of the T-Storm Watch with storms lined up from West Virginia through Kentucky.
Update 2:25pm: A Severe Thunderstorm Watch has been placed in effect for the I-81 Corridor west of the Blue Ridge until 9pm tonight. The greateast threat for severe weather will be in the form of damaging winds. Storms appear possible in the D.C. area closer to 4pm this afternoon. There has been a lot of lightning as well in these storms so be sure to keep your eyes to the sky before heading outside. Also, check Live Super Doppler Radar to check the latest position of the storms.
The Storm Prediction Center has placed portions of the D.C. area under a Slight Risk for severe storms. This is basically an area that has a higher liklihood for severe weather during the day. Just recently, a mesoscale discussion was put over our region because of on-going severe storms in Pennsylvania which will approach our region through the afternoon. The SPC puts out a mesoscale discussion prior to putting out a Severe Thunderstorm or Tornado Watch. Since today will be more likely for severe storms with damaging winds and large hail, a Severe Thunderstorm Watch may be needed soon for our area.
Timing: After checking out the progression of the front and keeping an eye on models that depict the line of storms traversing the region, I think timing will be around 4pm in the D.C. Metro when the storms begin to enter. They will continue through the early evening hours before pushing east.
Greatest Weather Threat: The storms are already beginning to form a line in Pennsylvania and Ohio and should progress to the east-southeast for the remainder of the day. I really think the highest threat will be in the form of damaging winds as winds aloft are around 60 mph and could easily be brought to the surface. Some isolated pockets of hail will be possible as well as frequent lightning.