Right mix of warm, humid air, winds stirred up state’s rare tornadoes

By Carolyn Y. Johnson
Globe Staff / June 2, 2011

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The tornadoes that struck Central Massachusetts yesterday are an unusual phenomenon for New England, the product of warm, humid air and winds that created the perfect conditions to generate the spinning, funnel-shaped storm. While the state does not have a large number of tornadoes, a National Weather Service meteorologist said there are typically one or two a year.

Tornadoes begin to form when warm, muggy air at the surface begins to rise and meet colder air above, creating thunderstorms. But by itself, that is not enough. There also needs to be rotation. This is caused when winds in the upper atmosphere blow in a different direction than the winds closer to the ground, creating a condition called wind shear.

“We look for moisture, we look for lift — lifting of air into the atmosphere and this turning of the winds with height — we got all that going together, and it was just perfect,’’ said Eleanor Vallier-Talbot, a meteorologist at the National Weather Service office in Taunton. “Everything just lined up.’’

The last tornado to hit Massachusetts occurred in July 2008, a waterspout tornado that started in Narragansett Bay and struck parts of Rhode Island and Southeastern Massachusetts. A destructive tornado occurred in 1995 in Great Barrington, killing several people. In 1953, Worcester weathered a major tornado that caused massive destruction and killed more than 90 people, one of the deadliest in the US.

In general, said Jerry Brotzge, senior research scientist at the Center for Analysis and Prediction of Storms at the University of Oklahoma, the Plains are prone to tornadoes because warm, humid air from the Gulf of Mexico mixes with cool, dry winds blowing off the Rocky Mountains.

“Whereas in the Northeast, our winds are almost generally from the west or southwest through the whole atmosphere — it’s a lot more difficult to get wind shear and strong updrafts,’’ Brotzge said.

Meteorologists said that although there is heightened awareness of tornadoes because of the storms in the South and Midwest this spring, there is no connection between those and the storm system that came through Massachusetts.

“It’s just bad luck this year. There’s no link we have between global warming, global climate change, and increased frequency of tornado,’’ said Josh Wurman, president of the Center for Severe Weather Research, a nonprofit research organization in Boulder, Colo., that receives funding from the National Science Foundation and has been working on understanding why many thunderstorms that are capable of causing tornadoes don’t — to enable better prediction.