Nor’easter had right mix

Altitude, differences of air masses key to snowfall variations

Jennifer Coppolino, with daughters, Jaya, 1, and Jazmyn, 10, retrieved items yesterday from their home in Athol, which was still without power after Saturday’s unusual October nor’easter.

The October nor’easter that dumped more than 2 feet of snow on parts of Massachusetts was not only unusually early, but it was also striking for the large variation in the snowfall amounts around the state.

The storm was the result of the collision of two very different air masses - cold air coming from Canada and humid, warm air moving up the coast. The storm buried some communities in snow and soaked others with rain primarily because of variations in temperature due to slight changes in altitude, said Charlie Foley, a meteorologist with the National Weather Service in Taunton. At sea level, where it was warmer, the precipitation tended to be rain or a little wet snow - whereas at colder, higher altitudes, as in Peru, Mass., which has an elevation 2,000 feet above sea level, it was 32 inches of snow.

Matt Noyes, chief meteorologist at NECN, said that ocean temperatures may have played a small role in keeping down snowfall totals near the coast, since the northeast winds were blowing in off a warmer fall ocean, rather than a chilly winter sea.

“It’s pretty typical that we see cold air masses come down from Canada and move into New England; October chill is not unusual for us,’’ Noyes said. “The unusual part is when October chill is followed by a return of warm air. It really is unheard of in October.’’

What made the storm’s impact even worse for residents was the fact that leaves are still on trees, collecting snow and weight.

Noyes said that there are larger forces at work, including La Nina - cooler than normal temperatures in the Pacific Ocean.

He also said that New England is in the midst of a 30-year cycle in which there has been an uptick in major storms, a pattern that he traced back to the Perfect Storm in 1991 that coincides with fluctuations in ocean temperature and salinity.

He said there was no reason to connect the current storm with global warming, a conclusion echoed by Foley. In general, climate change is predicted by scientists to increase severe weather events.

“An October pattern in no way dictates an entire winter pattern,’’ Noyes said. “However, this is the type of pattern that would be coincident with La Nina, so I wouldn’t be surprised to see a number of these heavy precipitation, mixed precipitation events’’ this winter.

Carolyn Y. Johnson can be reached at Follow her on Twitter @globecarolynyj.