Severe weather across this part of the country starts to become less uncommon as you move through August and into September, however, we are by no means immune to it! A developing and strengthening storm system will provide us with the potential for some strong to severe thunderstorms on Saturday along with some torrential rains.
A sharpening and deepening trough will slide eastward dragging along a cold front with it. At the same time an area of surface low pressure is expected to develop and rapidly intensify as it moves northward from the Tennessee Valley through western PA/NY and into southern Canada. This will allow a warm front to move northward through southern New England allowing for an unseasonably warm and moist airmass to advect into the region. Even with limited sunshine tomorrow temperatures should range from the upper 70's to lower 80's with dewpoints creeping perhaps into the lower 70's. This combination of warm temperatures and high dewpoints will lead to at least a marginally unstable airmass. some computer models are indicating the possibility of several breaks of sunshine tomorrow across the entire region. if this does occur and we can get a period of strong solar heating than the possibility of moderate instability will exist.
A piece of powerful shortwave energy is expected to round the base of the deepening and strengthening trough. With the shortwave interacting with the trough we will see winds aloft increase. Computer models are forecasting a low-level jet in excess of 30-35 knots with a mid-level jet of 45-55 knots and an upper-level jet streak of 90-100 knots placing the region in the right entrance region of the upper level jet. Computer models are also forecasting a great deal of helicity thanks in part to directional shear in the lowest 2km of the atmosphere and strong speed shear.
Given the presence of strong forcing/lift associated with the cold front and approaching trough and the potential for at least weak instability a squall line is expected to develop just out ahead of the cold front. Given the presence of very strong winds aloft, strong atmospheric mixing, and no inversion in the boundary layer this squall line would have the potential to produce strong to even damaging winds from it's entire journey from NY/PA all the way to the New England coastline.
We will have to keep an eye out for any discrete storm development out ahead of the main line as well. Given the presence of high helicity and long/curved hodographs as observed on skew-t soundings if enough instability materializes the potential will exist for isolated tornadoes as well. This threat could be further enhanced across the Hudson Valley of NY extending into southern VT as well as the CT River Valley. This potential will be monitored extremely closely.
If discrete development does develop it could happen as early as 3-4 PM with the main line moving through during the late evening and early overnight hours. While instability will decrease with the loss of daytime heating storng dynamics and forcing should help to sustain the line some as it gradually weakens with eastward progression, however, still possessing the threat for strong winds.
Given the presence of high dewpoints and lots of low-level moisture torrential rains will be likely as well, potentially leading to pockets of flash flooding.
While the entire region will be at risk for strong to severe storms the area with the greatest potential will be from eastern PA/NY extending into southern VT and through central CT/MA.
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