Tuesday, July 12, 2022 Thunderstorm Potential Update

Scattered showers and thunderstorms are expected to develop across New York and Pennsylvania Tuesday afternoon and progress east-southeast across the Northeast into New England ahead of an approaching cold front and developing pre-frontal trough. With the pre-frontal trough now in the picture, this may lead to earlier storm development. 

Severe Thunderstorm Potential 

The potential for widespread severe weather is exceedingly low, however, the potential exists for isolated-to-scattered pockets of severe weather across central/eastern New York down into Pennsylvania with severe weather potential more localized across New England. The greatest risk is for damaging wind gusts. 

In terms of the set-up there are actually some impressive ingredients. An unseasonably strong mid-level flow will overspread the Northeast with 50+ knots of flow at 500mb and 40+ knots of flow at 700mb. This will contribute to bulk shear values in excess of 40-50 knots over the region. This shear would be more than supportive of thunderstorm organization and with a predominately unidirectional flow this would support quick upscale growth into one or two line segments. Shortwave forcing is also pretty decent with much of the better forcing right along the international border:

Combination of surface temperatures climbing into the 80's with dewpoints surging through the 60's will contribute to about 500-1000 J/KG of MLCAPE into New England with upwards of 1000-1500 J/KG of MLCAPE farther west across New York and Pennsylvania. There are indications the pre-frontal trough may become established relatively early and well east. This would yield earlier cloud development and scale back temperatures and instability. Poor mid-level lapse rates and warm mid-level temperatures will yield a low ceiling on how much instability can develop.

How thunderstorms should evolve

With surface-based CAPE values approaching 2000 J/KG this will aid in the rapid acceleration of parcels to the LCL and subsequently the LFC as convective temperatures are reached. However, due to very poor mid-level lapse rates (5.5-6 C/KM), rather warm mid-level temperatures (500mb temps ~-8C), and mixed-layer CAPE only in the 500-1500 J/KG range, parcel acceleration through the mid-levels of the atmosphere will be reduced greatly. This will preclude more robust convection on a widespread basis. This is evident by tall skinny CAPE profiles which suggest a higher degree of water loading which will actually minimize the true CAPE.

Convection will begin to rapidly fire by early afternoon across central New York and Pennsylvania. The strong shear aloft will help aid in thunderstorm organization, however, the processes described above will hinder convection from becoming very deep and thunderstorms will struggle to intensify. With this said, combination of some steep low-level lapse rates (but this too could be impacted if full heating isn't materialized) and strong low-level winds will promote the risk for isolated-to-scattered damaging wind gusts within the strongest of thunderstorms. Given some signals for low-level winds to back a bit around the trough, a tornado can't be ruled out, especially if any thunderstorm can remain discrete.