The Storm Prediction Center has expanded the Slight Risk across much of Virginia, with the exception of a Marginal Risk across Far Northern Virginia and Maryland, and along the coast. Our “High Wind Threat Index” now reflects these changes, showing up to a 5, or 50 percent chance of a storm producing damaging winds within 30 miles of a given location.
The tornado threat remains the same, with a low-end chance of a few isolated tornadoes. The greatest threat will be across South Central Virginia as a few of these storms will likely be discrete supercells and fire up ahead of the main line. These storms would be capable of producing an isolated tornado. The surface wind flow ahead of the cold front appears to be more out of the southwest and this should decrease low-level helicity, preventing many of these storms from becoming discrete. Instead, we expect one or two lines of strong to severe thunderstorms, with straight-line winds being the main threat.
By early to mid-afternoon, showers and thunderstorms are expected to develop. The latest model guidance is trying to show two areas of showers and thunderstorms: The locally heavy rain and thunderstorms along the coast is possibly due to a low-pressure system developing off the coast. The main activity that we’ll be watching for severe potential will be across the Interstate 77 Corridor between 1:00 p.m. and 3:00 p.m. Monday.
Between 5:00 p.m. and 7:00 p.m. a line of strong to severe thunderstorms will move across the Central and Southern Shenandoah Valley and move into Central and Southern Virginia. We’ll be watching the southern extent of these storms across South Central Virginia and the Roanoke Valley for any of these storms to produce tornadoes as there will be enough low-level shear present.
Between 7:00 p.m. and 9:00 p.m., very heavy rain is expected across portions of the Virginia Piedmont, Delmarva, and Washington, D.C. and Baltimore Metropolitan areas. We’ll still need to watch for some of these thunderstorms to produce damaging wind gusts and an isolated tornado, especially southwest of Interstate 64.
By 9:00 p.m. into the early overnight hours, the severe threat will diminish, and we’ll be leftover with areas of heavy heavy rainfall, frequent lightning, and gusty winds. Isolated areas of localized flooding are possible where thunderstorms move across the same locations. Once the storm system finally moves offshore by early Tuesday morning, gusty winds will wrap back around the system for several hours, with gusts 20 to 25 mph possible through early Tuesday afternoon.
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