The massive heat dome that engulfed the Northeast this week will break down Friday as cooler air flows in and snaps the heat wave, bringing some relief to Boston and much of New England.
Officially this hot streak will go down as a three-day heat wave, with Tuesday’s high reaching 92 degrees; a record-breaking 98 on Wednesday, and Thursday’s near-record high of 97. Hot days and warm nights have boosted June’s average temperature over 5 degrees above average.
But on Friday, a slow-moving front will introduce a pattern change. Temperatures across Boston are expected to reach the low 80s by midday, then it will slowly cool down into the 70s throughout the afternoon as a shift in wind direction brings cooler air on shore from the north and east. Parts of central and western Mass. and Connecticut may still see temperatures break 90, extending the heat streak there before relief trickles in later in the afternoon.
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For the tens of thousands of fans planning to join the Celtics for the championship celebration Friday, much of the day will see partly sunny skies with building clouds and the chance for scattered showers developing around midday. A frontal boundary will keep a slightly disrupted pattern in place, especially with humidity levels remaining elevated.
The day will begin more humid and will slowly improve throughout the day, but still, dew points will remain elevated in the 60s, making it feel muggy out. Make sure you’re drinking plenty of water and wearing sunscreen at the parade.
Showers and thunderstorms that do manage to organize may end up having a little pop to them, bringing brief downpours to the areas they pass. Rainfall totals are likely to remain between a half inch and an inch, but I wouldn’t be surprised if some storms build and dump decent rainfall rates, bringing local amounts of 2 inches or more.
Friday’s breakdown
Southern New England: There will be two different levels of heat intensity across Southern New England today. West of Worcester and Providence may very well see temperatures jump back into the 90s, but east will see a break in the intense heat and remain mostly in the 80s. Regardless of where you are, you’ll still be dealing with elevated humidity with dew points in the 60s. Partly sunny skies will begin to fill with clouds as a front will introduce scattered showers and thunderstorms starting around midday. The afternoon will mostly be filled with on again, off again showers until things begin to dry out in the evening.
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Western Mass.: A mix of sun and clouds with temperatures building back likely towards the low 90s to continue the heat wave, especially across the Pioneer Valley. Temperatures will likely drop in the afternoon, but enough heating will still make the day hot. Dew points will still elevated, as well. Scattered showers will begin to develop around the region in the early afternoon.
Cape and Islands: Outside of dew points in the low 60s, much of the Cape and the islands will remain ideal with temperatures in the mid and upper 70s. Much of the day will consist of stretches of sunshine and groups of clouds. There may be an isolated shower that enters the region later in the afternoon.
Northern New England: The most consistent relief from the heat spreads through northern New England with the front passing early. A variety of sun and clouds is expected today with temperatures in the 70s and low 80s. Scattered showers and thunderstorms will develop along the frontal boundary and aid in keeping the region cooler than the last three days. The air becomes noticeably less muggy as the afternoon progresses.
Ken Mahan can be reached at ken.mahan@globe.com. Follow him on Instagram @kenmahantheweatherman.