Rare Risk of Tornadoes in New England on Sunday

Parts of New England and the Northeast were under an unusual risk for tornadoes on Sunday as severe thunderstorms were expected to strike the region, forecasters said.

The National Weather Service issued a tornado watch early Sunday afternoon for Massachusetts, Vermont, New Hampshire, northeastern New York and western Maine.

More than 8 million people were under the watch, which signals that conditions could lead to severe storms or tornadoes. The watch is in effect until 8 p.m.

The National Weather Service office in Albany, N.Y., warned of an enhanced risk of severe thunderstorms on Sunday afternoon and evening, and said such a risk was “more rare” for that part of the country.

An enhanced risk “corresponds to the potential for more persistent” and intense storms, placing it at the third level of a five-level scale for the risk of severe weather.

Strong to severe thunderstorms were also expected to affect western and central Massachusetts and possibly spawn tornadoes, according to the Boston office of the Weather Service.

“There is definitely the risk for a few tornadoes,’’ said Hayden Frank, a meteorologist with the Boston office, adding that the risk there would be mainly after 4 p.m. and into the evening on Sunday.

He said that “the greatest risk” for tornadoes would be in New Hampshire and Vermont.

The Weather Service office in Burlington, Vt., said on Sunday that a good portion of the area could see intense storms with damaging winds, large hail and possible tornadoes.

A combination of factors on Sunday were contributing to the tornado risk, said Bill Deger, a senior meteorologist with AccuWeather, including the heat that has been baking the region.

“We have the hot humid air moving into the Northeast,” he said, adding that a cold front was also moving from the west, approaching New England from upstate New York. He said that the other factor was that “wind direction is changing with height in the atmosphere, which increases the chance of thunderstorms to spawn tornadoes.”

Citing a database maintained by Iowa State University, Mr. Deger said that the enhanced tornado threat on Sunday was the highest in New England in six years.

While people typically think of the Plains or the South as tornado hot spots, they do happen in New England, Mr. Deger said.

He noted that this type of tornado risk “comes around once or twice each year for interior New England.”

Last summer, an EF zero tornado, which is rated as a weak tornado with winds of 65 to 85 miles per hour that causes minor damage, struck Vermont, Mr. Frank said.

“We don’t get these setups too often,’’ he said. “They do happen.”

On Saturday evening, a tornado touched down in Janesville, Wis., where it caused “considerable” damage to buildings and infrastructure, officials said.