As the coldest air of the young fall season swept across New England Sunday night into Monday morning, overnight low temperatures dipped well into the 30s for many, prompting frost advisories all the way south to the interior southern suburbs of Boston. Monday morning dawned with a thick frost for many, from Northern Maine to Central Connecticut and valleys of Central Rhode Island.
In Lakeville, Connecticut, weather observer John Hoffman reported a layer of ice atop the car, as heavy dew froze in the early morning as temperatures dropped into the middle 30s. It's worth noting - air temperatures as measured by the thermometer don't need to drop below freezing for frost to develop: it's all about the "laminar layer."
The laminar layer is a thin layer of air that surrounds all objects, only a few millimeters thick at its deepest point, and this laminar layer surrounds cars, blades of grass, rocks and just about everything else. Though the air temperature a few feet off the ground, as measured by our thermometers, may hover in the middle or even upper 30s, on an undisturbed night devoid of wind, the laminar layer can cool dramatically more, which is why frost develops even as measured air temperatures linger several degrees above the freezing mark.
As the sun rises, the laminar layer warms quickly, melting away the frost. Of course, coldest pockets saw enough cooling not only to generate frost, but to produce a hard freeze - temperatures dropping below 32and for some, a hard freeze of 28 or colder for three hours straight, though that was mostly only observed in Northern New England Valleys.
Perhaps most noteworthy of our chilly morning temperatures was Chicopee, Massachusetts, dropping to 30 degrees and setting a new cold record for the date, beating the old record of 32 set in 1949. Other cold spots, by state, included Norwood, Massachusetts, just southwest of Boston, at 28 degrees; Amston, Connecticut, hit 31 and took coldest spot in the Constitution State; Little Rhody saw Kingston drop to 33; Vermont's coldest spot of 26 in the Northeast Kingdom's East Burke is nothing exceptional by Vermont standards, but was enough to bring a hard freeze to town; Northern New Hampshire's town of Errol was coldest in the Granite State at 27 and Cupsuptic Lake in Oquossoc, Maine, dropped to 26.
Here in the NECN Weather Center, we don't expect temperatures to be anywhere near as cold Monday night, as warmer air and clouds begin streaming in ahead of a shot of rain expected Tuesday morning - rain that will serve as a precursor to a pattern shift that raises the chance for measurable rain that may total over one inch for some over the next week.