A round of severe weather is likely today in portions of the northeast; according to the National Weather Service’s Storm Prediction Center (SPC), the greatest threat of tornadoes will be over New Jersey and eastern Pennsylvania including the Philadelphia metro area. There is also a threat of tornadic storms over much of Delaware, Pennsylvania, Connecticut, central and southern Upstate New York, northeastern Maryland, and western Massachusetts. Including the area covered by the tornado threat, there is also a threat of damaging and destructive winds from straight line winds in the northeast. While not everyone will see a damaging wind gust or tornado in these zones, the probabilities of being hit by them are higher than normal today.
Water-vapor imagery this morning shows a potent mid-level shortwave trough moving southeast over the Upper Great Lakes towards the Northeast during the period. The primary upper vorticity max will rotate through the base of the larger-scale trough and through the St. Lawrence Valley, before an upstream disturbance west of James Bay this morning pivots southeast and reaches Maine and eastern Quebec early tomorrow. Surface analysis this morning places a 1004-mb low north of Georgian Bay and a cold front extending west-southwestward into northern Iowa . An attendant warm front arching southeastward through the Lower Great Lakes and draped over the Mid-Atlantic states will advance northward as the cyclone develops east towards northern Maine by late evening. Concurrently, the cold front will push southeast across much of Great Lakes into the Ohio Valley.
According to the SPC, south of the boundary, a very moist air mass was sampled this morning by different measurement tools reflecting upper 60s to lower 70s F dewpoints. A few thunderstorm clusters this morning have developed near the warm frontal zone from the Lower Great Lakes into the Mid-Atlantic states. The early day storm activity will likely be limited in storm vigor, due in part to initially widespread cloud cover inhibiting strong heating in the areas downstream over parts of Pennsylvania and New York. Gradual dissipation of clouds and heating coupled with the northeastward advancement of the warm sector will promote a broad area to become moderately to strongly unstable later today from the Ohio Valley eastward into the Mid-Atlantic and parts of the Northeast.
A belt of westerly strong winds in the mid levels of the atmosphere will flow from northern Virginia into the Northeast which will aid in storm organization and severe potential this afternoon and evening. The SPC says models differ substantially regarding evolution and timing of possible bands of storms and clusters with embedded cells.
“Regardless of specific details, it seems plausible several multicellular bands of storms will develop during peak heating and organize as these bands move east. Some of the more intense cells will potentially become supercellular posing an all-hazards severe risk,” warns the SPC.
“Potentially widespread damaging gusts , 50-60 mph, locally stronger 55-70 mph, perhaps paralleling the I-95 corridor from Chesapeake Bay into southern New England,” the SPC warns, adding that “A few tornadoes are possible both from linear and cellular storm structures given some low-level hodograph enlargement and moist low levels.”
Farther west, veered low-level flow ahead of the cold front will promote upscale growth into a few bands of cells and line segments across the southern Great Lakes into the Ohio Valley. Damaging gusts appear to be the primary hazard but the SPC says that a localized risk for hail and perhaps a couple of tornadoes may accompany this activity.
