By: Peter Forister, NOVA Storm Chasing & Denver Murray, Virginia Weather Action
Tuesday may be a busy day across portions of our coverage area. Damaging wind, supercells, and a tornado risk are all expected in a severe thunderstorm event tomorrow for the Mid-Atlantic.
The local National Weather Service and the Storm Prediction Center have outlined an area of enhanced severe thunderstorm risk for tomorrow (Tuesday) for Virginia, Maryland, New Jersey, Pennsylvania, and other areas of the Middle Atlantic. This storm risk is mostly for damaging winds which will be associated with a strong squall line, but there is a notable risk for rotating storms as well. Supercells and a couple tornadoes are expected in areas with the greatest shear and instability overlap.
The National Weather Service in Sterling, Virginia, says that two corridors of particularly severe storms are most likely, one along and north of I-70, and another south of I-66.
The biggest unknown is how the cloud cover develops in the morning hours, and that’s entirely based on overnight convection trends from the Midwest overnight, so it’s incredibly hard to pin it down exactly.
The most likely scenario is that a warm and clear sector develops mid-morning along and south of I-66 in Virginia, which will allow cape levels to approach 2000. The shear will also increase through the early afternoon with a approach of a mid level shortwave and decent 850-700 mb flow. A surface trough should form in the lee of the Appalachians which will provide a forcing mechanism for mid afternoon storms. Any that fire off that trough will have moderate cape and veering winds to work with, which should lead to a more isolated nature with supercellular structures. An isolated tornado would be possible with one of those storms across central Virginia, but the more likely scenario is hail and localized very strong winds.
Further north, the shear will be much better but the cape will be lower, so I’d expect some multi-cell structures with bowing line segments. An embedded supercell is more likely north of I-66, and any of those would have the highest tornado risk of the day. The main event will be forced by the high plateaus in West Virginia, and take advantage of late afternoon instability and downsloping to intensify as a squall line on approach to I-81. The line should push through the 95 corridor in the evening with widespread damaging winds and embedded tornado risk because of the high shear along the frontal boundary.
Models have been doing a poor job on timing over the past few weeks, as much of the activity has developed several hours earlier. Therefore, it’s possible this may happen again, especially, considering the warm, moist environment. Virginia Weather Action and NOVA Storm Chasing strongly recommends that you remain weather aware throughout the day and into the evening.
Stay tuned to weather warnings tomorrow, and follow your local trusted media and NWS office for more local forecast details.