Big heaping serving of summer heat today! Highs closed in on 90 in the Nashoba Valley: Pepperell, Groton, Chelmsford, Littleton, Ayer. Elsewhere, mid 80s were common all the way to Boston. Cooling sea breezes teased us at the coast, then they backed off in the afternoon as the southwest wind became more established.

Welcome to summer, right? Hang on. Certainly this will become the norm soon, but as I blog, a back door cold front is sliding out of coastal Maine with its sights set on Southern New England. Chilly temps in the mid 40s (!) are already popping up in the Mid and Downeast coast of Maine. Why does this matter? That’s the source of our cool down. These setups are notorious for sharp, sudden drops in temperatures, and by tomorrow you’ll be looking for a light jacket or sweatshirt.

Thankfully, the temperatures will make a comeback later in the week, so we’re not steeped in below normal chill for the entire workweek. The total reversal in temperatures will be the work of a developing cut-off low pressure system. Combined with an marked increase in humidity, slow-moving downpours, and a possible infusion of tropical moisture, I’m getting a little concerned for the possibility of heavy rain/urban flooding coming into the picture by late Friday and Saturday.

We’ll keep you posted.

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