Another tornado on Cape Cod? How twisters take shape and why they’re surprising meteorologists
This week marked the fifth tornado to hit Cape Cod in just four years, and experts warn that a warmer, wetter environment will likely mean even more in the future.
On Tuesday, two tornadoes touched down, one in Mattapoisett and one in Barnstable, taking down trees and wires as a downpour flooded low-lying roads across the region. Then on Thursday, the National Weather Service issued another caution for conditions that could produce a tornado.
The two twisters came just two years after a tornado touched down in Dennis, and four years after three tornadoes hit the Cape, knocking out power, and even ripping the roof off of the Cape Sands Inn.
They’ve surprised lifelong Cape Codder and meteorologist Phil Burt.
“I’d be lying if I said that I thought I'd ever even experience one, to be honest,” Burt said.
Since the beginning of 2015, he said, there have been 17 separate tornado warnings issued for Cape Cod. That doesn’t reflect the number of recorded tornados, but it is more than just about any other county in Massachusetts.
“[Compared to] the rest of New England,” Burt said, “the Cape definitely stuck out like a sore thumb.”
How tornadoes form on Cape Cod
For a tornado to form, a few key ingredients must be present. First, there needs to be a boundary where humid, muggy air clashes with drier and cooler air, usually along a cold front, like the one that passed over the Cape on Tuesday.
At the same time, the jet stream — which looks like a giant river of wind — had a sharp southward kink.
“And when we get those sharp kinks,” said Jennifer Francis, senior scientist at the Woodwell Climate Research Center in Falmouth, “that increases the chances of there being the right conditions for tornadoes.”
Then wind on the ground also needs to blow from one direction, while wind higher in the sky blows from a different direction — this is called wind shear.
It's that turning of the air with height that actually creates what we see essentially as a tornado or waterspout.
Tornadoes have historically been rare on the Cape, Coast, and Islands because the region tends not to have contrasts in summer air masses the way communities in the middle of the country do.
Mid-America can get cool, dry air coming from Canada, which runs up against moist air coming up from the Gulf of Mexico.
“So because we're on the coast, we don't tend to get that really moist Gulf air all that often. We do sometimes,” Francis said. “But because the ocean temperatures are so warm off our shores now, that's almost as good as the Gulf of Mexico being there. So it's supplying this really copious moisture that just wasn't as common a few decades ago.”
What role climate change plays in tornadoes locally
With warmer oceans and a warmer atmosphere, Francis said, more moisture is evaporating into the air. That moisture is the fuel that strengthens storms.
“It really does come down to putting moisture and more energy into the atmosphere. And that's exactly what we are doing by thickening the blanket of greenhouse gases around the earth,” she said.
To cut down on greenhouse gas emissions, experts say, communities must hasten the transition to renewable energy, electrify the transportation sector, protect the natural environment, and more.
It’s essential to fight the drivers of climate change because, Francis said, the added moisture in the atmosphere isn’t just fuel for tornadoes, but also nor’easters, hurricanes, and more storms.
“The climate crisis is upon us,” she said. “It's not this future thing to worry about. It's here now, and it's already affecting us in many ways.”