There are several types of thunderstorms that can affect southern New England. Thunderstorms can be broken down into 3 general categories:
  • Multi-cell storms
  • Single cell storms
  • Supercell storms
Single Cell Thunderstorms
Single cell thunderstorms are the most common type of thunderstorm to occur in Southern New England. They generally last 20 to 30 minutes and on occasion do produce brief and localized severe weather. These storms can be classified as pulse severe thunderstorms since the updraft usually pulses upward once, then it collapses in the form of a strong downdraft before dissipating. This sometimes results in localized downbursts, called microbursts. These, on occasion can produce brief wind gusts around 60 mph along with small to occasionally large hail.

Multi-Cell Thunderstorms
The second type of thunderstorm to affect southern New England is called multi-cell thunderstorms. They can come in the form of clusters or squall lines. Squall lines consist of several storm cells that are strung together in a line with a continuous gust front at the leading edge of the line. As the gust front moves forward, the cold outflow originating from the storm's downdraft forces warm and unstable air to rise into the storm's updraft. Squall lines can move as fast as 60 mph and their main threat is damaging winds. However, stronger squall lines can produce large hail and isolated tornadoes as well.

The most severe type of squall lines is called a Derecho. Derechos are usually very compact and can last for many hours. They have been known to produce straight line winds of over 100 mph. the Adirondack Mountains were hit by a severe Derecho during the early morning hours of July 15 1995. Almost 1 million acres of forest was damaged and several campers were killed. That Derecho moved southeastward and produced 80 to 90 mph wind gusts in portions of Massachusetts.

Supercell Thunderstorms
The third type of thunderstorm is the supercell thunderstorm. They are usually found in the plains states during the spring. However, they have been known to affect southern New England on occasion. Supercells are the most dangerous type of storm since they are responsible for producing most of the nation's tornadoes and tornado-related deaths. They also frequently produce very large hail and very strong straight-line winds.

The main characteristic that sets the supercell apart from other thunderstorms is its rotating updraft. It's this rotating updraft that allows the storm to last for several hours and produces many tornadoes. The rotating updraft is usually caused by strong wind shear in the mid levels of the atmosphere that works in tandem with strong instability. One of the deadliest tornadoes to ever occur in the United States was the Worcester, Massachusetts tornado of June 9, 1953. This long-track tornado was spawned by a supercell thunderstorm.

Always remember that deadly lightning accompanies every thunderstorm, whether it is severe or not.

Source: National Weather Service, Taunton, Massachusetts