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Heat Dome Sets Up for New England

The long awaited heat dome has set up to New England's southwest this morning, bringing with it soaring heat into the region. The peak of the heat will be Wednesday and Thursday, with widespread 90s across New England and some areas (mainly the lower Connecticut River Valley and Merrimack Valley) pushing toward 100°. The latest guidance has begun to shy away from areas hitting the century mark, however.

Surface map from Tuesday morning, showing the high pressure responsible for the heat dome near Maryland/Pennsylvania:

Not much has changed with the overall thinking of this heat wave and expected temperatures. It does look like guidance is generally leaning toward a majority of areas staying below a 105° feels-like temperature for Wednesday and Thursday as temperatures have trended ever so slightly lower.

This 105° mark is the threshold between a heat advisory and excessive heat warning. An excessive heat watch remains in effect for the Connecticut River and Merrimack Valleys, which will be either upgraded or downgraded later today. Heat advisories are in effect for Tuesday across a wide swath of New England.

The place to escape the heat will be south-facing coastlines, with places like the Rhode Island coast, Cape Cod and Maine's midcoast remaining cooler than everyone else., especially on Tuesday. Highs there may struggle to get out of the 70s on Tuesday and remain in the 80s on Wednesday and Thursday.

There's now mixed signals on whether Wednesday or Thursday will end up hotter, but this is really splitting hairs as it'll likely be a difference of a degree or two. Thursday has the highest "heat risk" for New England on the National Weather Service's New heat risk map. This is likely due to the potential cumulative effect of multiple hot days in a row.

Daily record highs will be possible on Wednesday and Thursday, but June monthly highs may now be just out of reach for cities in southern New England. Caribou, Frenchville and Houlton Maine are still looking to come very close to all-time high temperatures on Wednesday. Whether or not temperatures reach their full potential will come down to cloud cover and storm activity, as we've been saying for nearly a week now.

As far as potential storms go, coverage will be spotty and most likely across the northern tier of New England, mainly Vermont, on Tuesday and Wednesday. With that said, an isolated storm could pop up anywhere in New England from the excess heat and humidity. Thursday will be similar, with pop-up storms, but more areas will remain dry all day versus areas that see a storm. Any storm that does form will have the chance to bring with it strong winds. Stronger storms will be most likely in Vermont.

WRF-ARW showing potential weather Wednesday late-afternoon:

The ridge of high pressure looks to collapse southward on Friday as a cold front drops into New England, bringing temperatures back down. The timing of this front will be critical in determining how warm of a day it becomes. No matter what, it will remain warm, with most in New England seeing highs into the 80s, with southern New England well into the 80s. This could trend downward if the front trends toward an earlier arrival time. Some humidity will likely stick around as well.

The timing of the front will also play a large role in the extent of any thunderstorms during the day, and how strong they may be able to become. As of now, southern New England may have the higher threat for thunderstorms on Friday.

Weather map for Friday morning:



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