Strong and severe thunderstorms possible Saturday

While lower dew points have been very well received in our area over the past several days, a warming trend will be underway once again by Friday. Increasing temperatures and moisture will become notable as winds, which had been coming inland off the area waters for the past few days, with to a warmer southwesterly direction. A transient ridge building overhead will aid in the warming temperatures moving into the Northeast US on both Friday and Saturday.

To our north, meanwhile, an expansive disturbance over Southeast Canada will begin shifting southeastward through parts of the Northeast US. While forecast models don’t currently show a strong or robust area of vorticity with this disturbance, the very broad disturbance has expansive height falls of its own. These act to supplement lift in the atmosphere along a cold front, which will be dropping southeastward through the Northeast states on Saturday.

Most of this would occur without fanfare, if it weren’t for the very warm and unstable airmass building over our area on Saturday. Forecast models are in good agreement that moderate to high instability will build into the area during the afternoon hours. Surface based CAPE may exceed 2000 j/kg, with MUCAPE values approaching or exceeding those values as well. Juxtaposed with the incoming front and height falls, this instability will act as ample fuel for strong to severe thunderstorms.

Supporting the organization of thunderstorms will be wind shear in the mid levels of the atmosphere. Forecast models are in good agreement that 40 to 50 knots of shear at the 500mb level will allow thunderstorms to become organized as they move southeastward through the Northeast States. One potential limiting factor could be the lack of depth to this shear — in other words, sufficient wind shear exists in the mid levels but not in the low levels nearer to the surface.

Thunderstorms should develop near the cold front during the early afternoon, over parts of Pennsylvania and New York state, and then shift southeastward toward our area later in the afternoon. The exact severity of the storms will depend on more intricate details, such as the magnitude of wind shear as well as the instability that actually builds throughout the area.

Overall, however, it appears the chances for strong and severe thunderstorms are higher than normal on Saturday. Torrential rain, lightning, and gusty winds will be the main threat with these thunderstorms, especially given the opportunity for downward momentum transfer (DCAPE) being depicted on forecast models at this range.

Stay tuned for updates as the threat comes into better focus over the next several days. As always, the Premium Dashboard will have the latest information from our forecasters.