The system that brought tornadoes to Arkansas Monday has its focus set on the Appalachian Mid-Atlantic region Tuesday as it tracks northeastward. Though the upper-level trough supporting the severe weather dynamics has since weakened and broadened, the corridor of soupy, sticky air has expanded in suit. Not only are all modes of severe weather possible, but flash flooding will be an additional threat that will act to compound the impacts from this severe weather.
The surface cyclone associated with the upper-level low pressure system was straddling the southern shore of Lake Michigan early Tuesday morning. The upper low was centered just to the northwest over the lake, with its sights set for eventual progression into Québec early Wednesday. The cyclone’s warm front was draped across the I-90 corridor, encapsulating the Ohio Valley and inland Mid-Atlantic with clouds and showers, just east of the upper-low’s center. The showers will progress northeastward throughout Tuesday morning, but the clouds may linger throughout the day, with breaks of sunshine possible in the afternoon. The cyclone’s cold front will not pass through the region until the overnight hours, but the storms it spawns Tuesday afternoon will race ahead of the front.
The clouds will be critical in inhibiting an otherwise ideal setup for widespread severe weather. Modest instability will build behind the warm front, from eastern Lake Erie southeastward to the Delmarva coast. A robust low to mid-level jet stream is forecast to develop just ahead of the cold front. This jet will enhance upward motion near its southeastern and northwestern peripheries as well as increasing wind shear along its axis, which will pass through northwestern Virginia through western New York. Additional upward motion from the jet will make up for the cloud cover inhibiting convection. The wind shear it will bring with it will be essential in maintaining storm updrafts, permitting storms to take full advantage of the potential energy supplied by the warm air-mass.
The broad region of lift will regenerate thunderstorms just behind the morning’s showers and ahead of the cold front early Tuesday afternoon, from southern Ohio all the way to the Gulf Coast. Any peaks of sunshine will enhance the storms’ growth. Heavy, widespread downpours will develop along the axis ahead of the front and the corridor of severe storms. Individual storms will swiftly progress northeastward, but the slow progression of the front will mean additional storms will immediately follow, prompting a significant risk for flash-flooding.
Isolated supercells will likely develop Tuesday afternoon west of the Appalachian mountains. Strong low-level shear and low cloud bases will support an isolated threat for a brief tornado. Otherwise, with the lack of cold air, hail is unlikely, deferring the primary threat to be damaging wind gusts. Akron, Erie, Pittsburgh, Buffalo, and Roanoke are at risk for feeling the impacts of these supercells. By the middle of the evening rush, the storms will have merged into linear structures as they approach the Appalachian mountains, where wind and flash flooding will be the only threats. Storms will continue into the overnight hours until the cold front finally passes.
Residents and visitors of areas at risk for severe storms and flash flooding Tuesday are encouraged to pay close attention to weather alerts. With wet antecedent conditions, heavy rain may result in flood waters rising rapidly, especially in valleys and along creeks and rivers, Additionally, given the heavy rain, any tornadoes that do form may be hard to see, so alerts from the National Weather Service will, as always, be the best source for precautionary measures.