Polar vortex may bring rare May snow to US East

Temperatures may also plummet to record lows for the month

BOSTON — The northeastern U.S. is about to get a cold spring farewell from winter’s bad boy, the polar vortex, which could bring rare May snowfall and record-low temperatures to some areas over the Mother’s Day weekend, forecasters say.

The polar vortex is usually a batch of cold air that stays trapped in the Arctic all winter, but a couple of times during the season, it wanders south, and brings bone-chilling cold and snow to Canada and parts of the United States. This year, the polar vortex stayed put and the East had an unusually mild cold season.

Around this time of year, the polar vortex breaks up, but this breakup is a bit different, said Judah Cohen, a winter storm expert for Atmospheric Environmental Research, a commercial firm outside Boston.

“The polar vortex didn’t do much the whole winter, but on the way out, I guess it kind of sent a message: Just because I didn’t do much this winter, don’t think I can’t,” Cohen said Thursday.

A low pressure system off the coast of southern New England is pulling cold air down from the north, Alan Dunham, a meteorologist with the National Weather Service in Norton, Massachusetts, said Thursday.

Forecasts called for perhaps as much as 2 inches of snow in the Berkshire Mountains in western Massachusetts on Friday into Saturday; an inch or so on grassy areas of central Massachusetts, southern New Hampshire and western Connecticut; and rain with a few flakes possible in the Boston area, he said.

Massachusetts hasn’t had measurable snow in May since 2002, when 2-3 inches fell in the Berkshires. There hasn’t been measurable May snowfall in Boston since 1977, Dunham said.

Upstate New York could see an inch of snow, and further down in New York City and the Hudson River valley is likely to see mostly rain, according to Hunter Tubbs at the National Weather Service in Gray, Maine.

Temperatures may plummet to record lows. The May 9 record low in Boston is 35 degrees, also in 1977. Freeze warnings are in place for parts of Pennsylvania, Tubbs said, with freeze watches stretching into New Jersey and as far south as Maryland.