A rapidly deepening trough will be working eastward through the eastern United States dragging a cold front along with it. At the same time an area of surface low pressure is expected to develop across the TN Valley region and work northward along the cold front swinging a warm front northward. Computer models are generally in agreement that this warm front will lift northward through the NYC area and then stall across central CT. South of the warm front the airmass will become very moist with dewpoints potentially rising into the lower 70's as far north as the NYC area and even into portions of southern CT. North of here dewpoints will be into the mid and upper 60's. Where the lower 70's dewpoints occur this will yield to an airmass which will become marginally unstable. Computer forecast models develop anywhere between 500-1000 J/KG of MLcape.
Wind fields aloft are expected to become quite strong for this time of year. Computer models are generating a 45-55 knot low-level jet working into the region, however, computer models have slowed down on the timing of the core of this jet getting into southern New England. The mid-level jet is expected to increase to 60-70 knots with a 80-90 knot ULJ moving nearly overhead as well.
The combination of modest instability along with very strong wind fields aloft will yield to the potential for some strong to even severe t'storms tomorrow and there will be two storm modes we may have to deal with.
1) With the northward movement of the warm front the potential will exist for isolated low-topped supercells to develop. Very similar to what we saw occur last Saturday where two confirmed tornadoes were confirmed in the NYC area. This potential is dependent on how buoyant the boundary layer can become and how much instability can develop. Where dewpoints get into the lower 70's this would be enough to yield a very buoyant boundary layer and be enough to create modest instability. The best potential for this will likely be from NJ up through NYC area and into extreme southwestern portions of CT.
2) Narrow low-topped squall line associated with the cold front. Extreme forcing along the front and a moisture rich airmass is expected to lead to the development of a very narrow low-topped squall line. While thunder/lightning may be limited this line could be strong enough to bring down some of those stronger winds aloft yielding to a threat of damaging winds. This line would move through eastern NY/southern New England probably after 9-10 PM.
With the main piece of shortwave energy expected to move north-northeasterly this means eventually the developing line will begin to ourtun the stronger forcing and dynamics aloft. We actually saw this occur last Saturday as well which was a main reason for the line rapidly weakening as it approached southern New England. As this line moves through central/eastern PA into SE NY and towards southern New England it will once again weaken.
With such strong winds aloft tomorrow and just above the surface tomorrow will be quite breezy as well, even without shower/t'storm activity. Winds could gust as high as 30-40 mph region wide with the strongest winds occurring across the coast and areas above 1500'. In fact, for elevations above 1500-2000' winds at the peak of the event could gust as high as 60-70 mph...perhaps even upwards of 80 mph! This will likely happen across the Berkshires and into the Green/White mountains of VT/NH!
Torrential rains will be likely tomorrow as well and this could lead to pockets of flash flooding.
Below is a graphic indicating areas of greatest wind and severe weather potential.
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