Atmospheric ingredients are coming together to create a weather situation in which severe storms will likely blossom across a large part of the Northeast and Mid Atlantic; due to that, the National Weather Service’s Storm Prediction Center (SPC) has issued Severe Thunderstorm Watches for southern Vermont, New Hampshire, Vermont, and New York including the entire New York City metro region, all of New Jersey, Delaware, Rhode Island, and Massachussetts including the Boston metro region, eastern Maryland and Pennsylvania including the Philadelphia and Baltimore metro regions, much of Virginia and all of Washington DC, and portions of North Carolina, Tennessee, and Kentucky.
Widely scattered to scattered severe thunderstorms with damaging winds are possible over southern New England into the Mid-Atlantic and Missouri through this evening. Large hail and strong-severe outflow gusts are also possible this evening into tonight across the central/northern High Plains. The SPC also says there is an elevated tornado risk in portions of the northeast; right now, they say the greatest odds of tornadic cells are over New Jersey, Connecticut, Rhode Island, Delaware, eastern Maryland and Pennsylvania, southeastern New York, and most of Massachussetts.
According to the SPC, a convectively-augmented midlevel trough and belt of strong midlevel air flow will continue eastward today over Pennsylvania and New York as an associated weak surface cyclone likewise develops east. Surface heating in cloud breaks this afternoon is helping destabilize the atmosphere, setting the stage for a severe weather outbreak. Scattered thunderstorms are expected to form by mid afternoon along the surface wind shift/front and along differential heating zones and spread eastward through this evening. The SPC says that data suggests that damaging winds will be the main threat with a mix of multicell clusters and some supercells this afternoon into this evening.
Additional clusters and bands of storms are expected this afternoon from eastern Kentucky and Tennessee into western Virginia along a diffuse outflow/front. This area will lie along the southern fringe of the westerlies aloft, but thermodynamic profiles will favor occasional downbursts with wind damage.
Within the Severe Thunderstorm Watch area, the local offices of the National Weather Service will issue Severe Thunderstorm Warnings and Tornado Warnings for specific counties when a threat materializes. Even before those warnings are issued, the National Weather Service is urging people to know what to do and where to go when they are issued. They also want people to make sure they have a way to get, hear, and act on any warnings that may be issued for their area.
The threat of severe storms and tornadic cells will diminish later this evening, giving the Northeast and Mid Atlantic the opportunity to have calm, dry conditions tomorrow.