Significant Severe Weather Event Possible Wednesday

It appears all the parameters are in place for what could be an unusually significant severe weather event in the northeast. It’s impossible to say whether Connecticut will be ground zero for the strongest storms but it’s quite possible we get whacked tomorrow afternoon.

Our computer models show strong lift developing by afternoon as a cold front moves in from the west along with upper level divergence as a shortwave trough advances. Plenty of instability is forecast with heat and humidity under a remnant elevated mixed layer. Shear is looking very impressive with 0-6km bulk shear of 35-40 knots and turning of winds in the low levels of the atmosphere which indicates tornado potential.

Here’s the 18z GFS forecast hodograph for 5 p.m. tomorrow in Hartford.

The clockwise turning of winds with height indicates enough low-level directional shear for tornadic supercells. Another way to look at that is a 0-2km helicity value of 174 m2/s2 which is impressive for southern New England.

There are several things that can occur to mitigate the severe potential tomorrow. Inlcuded in this list are morning and midday cloudiness from upstream convection, drier air at the surface that mixes down or advects in from the west before the best “lift” arrives, poorly forecast lapse rates (EML fails to arrive), or too much mid level dry air which effectively chokes updrafts because of excessive dry air entrainment.

As always summer storms are fickle and are guided by very small scale perturbations that are difficult to resolve an hour ahead of time, nevermind 24 hours! That said I think a significant severe weather threat exists across western Connecticut, Massachusetts, and adjancent New York tomorrow afternoon. Damaging winds, large hail, and tornadoes will be possible.

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