UPDATE 2 PM: Tornado watch issued; severe storm risk for all of Virginia today, but greater to east of Roanoke
A cold front is pushing into warm, moist air ahead of it today, with some degree of shifting winds aloft. That is a recipe for a substantial severe weather threat over the state of Virginia. There are some uncertainties in that seemingly straightforward forecast. One is the current showers and cloudiness over much of Southwest Virginia that could limit warming and therefore destabilization of the lower layers of the atmosphere. Also, as the National Weather Service-Blacksburg points out in its morning discussion, there may be a chance of the “Blue Ridge jump,” where a storm line forms far to the west and then re-forms east of the Blue Ridge, with the stronger storms skipping over some or all of the New River and Roanoke valleys. All that said, there is enough lift with the cold front and certainly enough moisture that strong to severe storms will be a significant possibility during the afternoon. Strong downburst/outflow winds will be the greatest severe risk for Southwest Virginia, as shown on the Storm Prediction Center’s morning map rating the chance as high as 30 percent of occurring within 25 miles of any given point. The tornado risk is greater mostly north and east of our region, owing to somewhat better atmospheric shear and greater instability with more daytime heating. There will probably be a few tornado reports in central/eastern Virginia later today, though a large tornado outbreak on the scale of those of April 2011 does not appear to be likely. The pattern is more that of a strong summer severe setup rather than a spring outbreak. The more the sun shines at your location and the farther east you are, the better your chance of high winds, large hail and isolated tornadoes in storms today.
Being in the field with the Virginia Tech storm chase in the Oklahoma/Texas panhandle region -- the only other slight risk of severe weather on the Storm Prediction Center’s map today, where coverage will be much less than Virginia but the potential for supercells higher — I will be unable to provide ongoing updates today. You can follow radar and the latest watches and warnings on the Radar / Future Cast link in the right margin of this blog.