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Aug 03, 2023

Tornado trends in New England: How active are twisters in 2023?

By Katelyn Umholtz Five tornadoes touched down in New England two Fridays ago, the strongest one in Rhode Island reaching an EF-2 strength for the first time in nearly 10 years. This year already,

By Katelyn Umholtz

Five tornadoes touched down in New England two Fridays ago, the strongest one in Rhode Island reaching an EF-2 strength for the first time in nearly 10 years.

This year already, there have been four days when tornadoes were reported, and 13 tornado warnings issued in southern New England, according to the National Weather Service. And it has not stopped raining, as anyone in the region would tell you, resulting in one of the wettest summers on record.

But are the tornadoes — and severe weather that causes the tornadoes — actually worse this year? And are we seeing a trend of tornadoes worsening? It depends on how you look at it.

According to NWS meteorologist Kevin Cadima, who looked at how many tornadoes southern New England has seen every year for the past 10 years, this year has seen more twisters.

“It’s certainly more active than a typical season,” Cadima said.

The local NWS office keeps track of the number of tornado days and tornado warnings issued. Keeping track of an individual tornado count can be inconsistent and is more likely to change over time.

To date, Cadima said there have been four tornado days across the parts of southern New England that the Boston NWS office monitors. At least one of those days, that Friday, Aug. 18, had more than one tornado touch down in one day.

Cadima pulled the last 10 years of tornado days to see how 2023 compared to years past:

The average number of tornado days in southern New England is typically two days. Cadima acknowledged the last six years, however, have recorded higher-than-average days of twisters.

These numbers are still relatively small compared to the amount of tornado activity that occurs in the Midwest and Southeast. And when measured on the Enhanced Fujita scale, New England typically sees tornadoes measured at EF-0 or EF-1. The EF-2 from that Friday was the first EF-2 since 2014 in southern New England.

But to really see if there is a trend, you have to look back even further in time, said Todd Moore, the Department of Geosciences chair at Fort Hays State University in Kansas.

Since 1954, Moore’s research shows that the number of tornadoes has stayed constant, but the number of tornado days has actually dropped in the Northeast.

“What that means is when tornadoes are happening, more of them are happening” in one day, Moore said. It’s what happened on Aug. 18 in New England, when one storm blew through and produced five confirmed twisters to touch down in different parts of the region.

Moore’s research, published in the International Journal of Climatology in 2017, shows that from 1954 to 1974, the annual number of tornadoes in the Northeast was 24. That number went up to 28 from 1975 to 1995, then back to 24 in 1996 to 2016.

For the average number of tornado days in the Northeast, the number dropped from 15 in 1954-1974 to 11 in 1996-2016. In those same time periods, the average of tornadoes per tornado day has increased from 1.5 to 2 twisters.

Moore noted the average isn’t a huge increase.

“The key is New England doesn’t have a bunch of days with many tornadoes,” Moore said. “But over time those tornado days with multiple tornadoes seem to be becoming more common.”

This is especially true for areas like the Southeast and Mid-Atlantic and less so for areas like the Great Plains, as “Tornado Alley” shifts more east.

Cadima and Moore both cautioned that even though these multi-twister storms are growing more common, it’s still pretty rare in New England.

What isn’t rare in New England, especially this summer, are storms.

The warmer atmosphere and increase in humidity creates atmospheric instability. It’s those ingredients that are a recipe for a thunderstorm. And when there’s a thunderstorm, there’s a risk of a tornado producing. All it needs to spin up is a favorable wind shear profile, Cadima said.

“Most of our tornadoes are from the tropical environment, where you see a lot of thunderstorms and you get a spin up,” he said.

The kind of storm that a tornado might follow is becoming more common across the country, Moore said.

“The environment for severe thunderstorms is increasing in the Northeast,” he said. “It’s increasing all over the U.S. As the lower atmosphere warms, and as we get more humidity in the air because of the warmer atmosphere, we do have more fuel and a better atmosphere for thunderstorms.”

It can be hard to observe tornado trends through a climate lens. Researchers don’t have decades upon decades of data to sift through with tornadoes like other types of weather events, and also tornadoes are harder to model because of their size and how they occur.

But what scientists have been able to decipher, Moore said, is that climate change is increasing temperatures and humidity, therefore instability is going up.

This is especially true for the eastern third of the U.S., particularly the Southeast, but also the Mid-Atlantic and the Northeast.

Lauren Casey, a meteorologist with Climate Central, said New England has had anywhere between 10 to 40 more days than normal when the instability was high enough to produce severe storms.

“Some of the biggest increases were observed in the Northeast during the summer months,” Casey said. Increases in instability were also notably higher along the coast in New England, according to a Climate Central analysis.

Increases in instability mean a higher likelihood of severe weather, and that brings storm warnings. Cadima said southern New England has seen increases in tornado warnings this year compared to the last 10 years. NWS Boston has released 13 warnings so far this year. NWS has seen other years in the last 10 years with more than 13 warnings, but the average number of tornado warnings released in a given year is nine.

Moore urged caution when using warnings as a way to tell if tornado activity is growing over time because it can depend on the forecaster. NWS releases tornado warnings when radar shows that a storm is rotating.

It’s too soon to tell if tornadoes will significantly trend upward in New England and the Northeast, especially because it’s really hard to tell how climate change impacts wind shear, one of those main ingredients in tornado formation. But what researchers are finding is that severe weather is becoming more of a reality for more Americans, including those in New England.

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