Frontal System to Bring Rounds of Storms Sunday to New England

New England’s next system will approach Saturday night and Sunday. This will be in the form of a frontal system with a warm front lifting across the region Sunday morning followed by a cold front later in the day. This will provide the basis for rounds of scattered showers and thunderstorms throughout the day. This will also bring a one-day return of high humidity.

The overall setup for Sunday is messy as it will involve multiple waves of energy moving across New England. This will bring scattered showers and thunderstorms to different parts of the region at different times of day. Initial energy will likely develop overnight tonight into Sunday morning, which will bring showers with embedded thunder to northernmost New England.

The main system's warm front will be lifting into southern New England in the morning as well, potentially setting off scattered storms across southernmost New England as well. As the frontal system's cold front drops southward, it will likely ignite another round of scattered storms from northwest to southeast in the afternoon through the evening after a period of mainly dry weather.

Below: FV3 showing potential weather Sunday morning (1st image) and around Sunday mid-afternoon (2nd image):

The afternoon line of storms will have the best chance to produce scattered strong to severe storms. The best chance for stronger storms to develop will be across southern and central New England as the cold front will likely cross these areas during peak daytime heating and instability. There will also likely be generally less activity across southern New England in the morning versus northernmost New England.

The four main ingredients for severe storms will be in place for New England. There will be abundant shear to allow storms to organize and strengthen and sufficient instability with CAPE values to the 1,000-2,000 range (highest across southern New England). Moisture will also be abundant with dew points well into the 60s. Lift will be provided by the cold front, crossing the region at a favorable time. The main question will be how much clearing can occur after the morning round.

Should plenty of clouds linger for a while, the severe threat will be lowered in the afternoon as instability will end up getting capped. Another limiting factor will be rather weak lapse rates (the rate of temperature decline with altitude). Should severe weather struggle to form, these will be the reasons. Damaging wind gusts will be the primary threat with large hail possible as well, especially across central New England. Localized flash flooding will also be possible given the moisture-rich environment capable of producing torrential rainfall.

Outside of the thunderstorm, it will be a very warm and humid day. While the clouds and scattered storms will prevent temperatures from reaching their full potential, widespread highs well into the 80s will be likely for central and southern New England. It'll be cooler for the northern tier as the front crosses earlier and generally more clouds are expected. Sunday will feel oppressive with humidity, making it feel warmer as well.

The system’s cold front will flush the humidity back out as quickly as it built in. Monday and Tuesday will again have lower humidity and cooler (by mid-July standards) temperatures. Both heat and humidity look to trend back up later next week as a heat dome is set to build over the south and midwest. New England currently looks to escape this heat dome’s full wrath as temperatures are unlikely to swell well into the 90s, though trends will be watched.

Below: 6-10 day temperature outlook, showing the heat dome likely falling short of New England: