Friday, May 15, 2020 Thunderstorm and Severe Weather Potential

A warm front is expected to lift through southern New England Friday morning which may produce a few showers or a rumble of thunder. As the warm front lifts into central New England dew points south of the front will climb through the 50's and into the lower 60's. As clouds begin to break, strong May sunshine should help boost temperatures through the 70's during the afternoon. The combination of temperatures in the 70's and dew points into the 60's will result in a modestly unstable air mass.

A cold front begins to approach southern New England by early evening. The combination of a modestly unstable air mass, strong wind shear aloft, and forcing from the approaching cold front and shortwave energy yielding strong height falls, will result in the development of rain and thunderstorms in the form of a squall line. This squall line will move southeast through the region during the evening hours and will be capable of producing damaging wind gusts.

Assessing severe weather potential:

The potential is there for a more significant severe weather event (despite the presence of steeper mid-level lapse rates), however, not all the ingredients will align to make this happen. Forecast models stall the warm front across central New England. Just south of the warm front the air mass will be unstable thanks to warm temperatures and humidity along with rather strong wind shear; including the presence of directional wind shear (winds changing direction as you ascend from the surface through the lower atmosphere). In this scenario, the potential would be there for supercell thunderstorms capable of producing tornadoes, however, this potential will be mitigated by the lack of a trigger and rising heights through the afternoon.


As the cold front approaches during the evening and the associated line of rain and thunderstorms, instability will begin to weaken due to the loss of daytime heating, however, strong wind shear aloft and just enough instability will keep the potential for scattered pockets of damaging winds and hail possible as the line of thunderstorms progresses southeast through southern New England. Expecting the line to begin moving through between 7:00 PM EDT and midnight EDT. Greatest risk for any damaging winds north and west of the I-84 corridor. There is the low probability for a tornado across southern VT/northwestern MA in the vicinity of the warm front as there will be enough wind shear to yield the potential for an embedded supercell within the line.