This renewed heat wave will likely peak today with highs reaching into the mid 90s for much of southern and central New England. Heat and humidity will continue into Wednesday before relenting by Thursday afternoon. With dew points into the 70s in places, it will create feels-like temperatures over 100°.
Without a strong ridge of high pressure over New England during this heat wave, it opens the door for thunderstorm development. On Tuesday, this will come as a weak disturbance rotates around a broader area of low pressure near the Great Lakes. This will allow a cluster of thunderstorms to develop this afternoon in New York before pushing toward New England later in the day. Storms likely won't arrive in western New England until this evening.
HRRR showing potential weather early this evening:
This line of storms will be strongest across western New England, but will likely weaken (and weaken rather quickly) as it pushes eastward thanks mainly to the late arrival time. The greatest chance for strong to severe storms will be across southern Vermont, the Berkshires and western Connecticut. Damaging winds will be the primary threat with a lower hail and tornado threat.
As far as the ingredients for severe thunderstorms go, shear will be strongest across western (and northern) New England. Lift will come eventually thanks to the disturbance wrapping around the trough north of the Great Lakes. Instability will be decent for stronger storms (CAPE values will reach 1,000+ in some areas) and there’ll be plenty of moisture with the excess heat and humidity.
With ample moisture in the atmosphere, intense rainfall rates will also be a possibility across western New England. The Weather Prediction Center has western Vermont and Massachusetts in the “marginal” category (level 1 of 4) for excessive rainfall. Northern and central Vermont remain especially susceptible to flash flooding after last week’s flood event.
The threshold for flash flooding is still as low as 1 to 1.5 inches in an hour and 1.5 to 2 inches in three hours across northern Vermont. The good news is that it's looking like the core of the storms will remain to the south of the hard hit areas last week.Overall, the flooding threat is low, but with flash flood guidance remaining so low across northern and central Vermont, it’s worth bringing up.
Heading into Wednesday, that trough north of the Great Lakes will lift north of New England. This will send a cold front into New England Wednesday night. Ahead of this front will likely see thunderstorms form by mid to late afternoon across western New England and arriving in eastern areas by the evening. There’s still some uncertainty on storm timing for Wednesday as it will come down to the positing of the cold front. Storms will likely be more scattered around rather than an organized line or cluster like Tuesday.
HRRR showing potential weather around mid-afternoon Wednesday:
The greatest threat within severe storms on Wednesday will again be strong wind gusts. The large hail and tornado threats are very low to none. There will also be the potential for intense rainfall rates within storms once again. The greatest chance for stronger storms will again be across western New England. Dynamics won’t be as good for Vermont, so their threat will be lower compared to Tuesday for the most part.
Overall, there may be a better chance for stronger storms on Wednesday, especially for areas farther east in New England. The potentially earlier arrival time of storms will help keep storms stronger farther east.
There will likely be higher instability farther east with CAPE values building to the 1,500 to 2,000 range. Shear will also be stronger farther east on Wednesday. Still, the timing of storm development favors the best chances of severe weather over western areas, but a couple stronger storms could have an easier time sustaining themselves into eastern areas.
Euro showing potential CAPE values in the late afternoon, showing the more unstable values farther east:
Heading into Thursday, the cold front will clear New England with falling humidity through the day. Building high pressure to the west will switch the persistent southwest flow to a much drier northwest flow. Temperatures will drop as well, but will likely remain in the 80s, and potentially well into the 80s in places as there’s no really cool air across western Canada to drop into New England as a major heat wave in the west continues. Humidity should remain tamped down through the weekend and into early next week.
Weather map for Saturday morning. This setup should result in a very pleasant summer weekend:
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