A cloud lowering associated with tornadic activity near Sandwich, Mass., on Tuesday. (Rob Craig via Facebook)

Cape Cod is a fun summertime vacation destination, and the weather is usually turning increasingly wintry this time of year. Tuesday, the Cape looked more like Oklahoma than New England as several tornadoes tore through Massachusetts and Rhode Island.

At least three tornadoes seem likely to have touched down. It’s a region that doesn’t see many twisters any time of year, and this is as late as they come in Southern New England.

Storms really started cooking after lunch on Tuesday as a pocket of cold air at high altitudes moved into the region. A funnel cloud touched down on the Cape Cod Canal in the early afternoon. “I was parked there and saw the clouds swirling down,” said Matt Fetzer, a history teacher in Hyannis who saw the tornadic vortex. “That’s when I booked it and got the heck out of there,” he said.

The whirlwind danced for several minutes before trekking east and dissipating as it moved onshore in Sandwich, Mass., near the entrance to Cape Cod. This marks the first confirmed waterspout on the canal since Aug. 20, 1997. And since it made contact with land, it probably can be classified as a tornado as well, which could make it the first confirmed on Cape Cod since 1977.

The National Weather Service in Boston later issued a tornado warning at 3:34 p.m. for the northern suburbs of Providence as a low-topped supercell raced by. It confirmed Tuesday night that a tornado touched down in Lincoln, but the strength and path length has yet to be determined.

This storm continued to produce as it moved east. Damage was reported in Norton, Mass., where a third tornado was confirmed by the Weather Service.

The most remarkable supercell of the day spun up just before sunset. It took the same path as the first — sailing eastward into the Cape Cod Canal before dropping a massive tornadic waterspout just offshore. It may have clipped the shoreline as well. The spout intensified about a mile east of Scusset Beach, a popular tourist destination. Winds of 100+ mph probably accompanied the vortex over open water.

At least half a dozen other reports of offshore waterspouts were received Tuesday afternoon from coastal Rhode Island and Southeast Massachusetts. The Weather Service is dispatching meteorologists across southern New England Wednesday to do storm surveys.

The cause for a late-season tornado swarm

To get rotating storms, two basic ingredients must overlap: instability (known as CAPE to meteorologists) and shear. CAPE — or Convective Available Potential Energy — is a measure of how much “juice” there is in the atmosphere. The more CAPE, the better the air’s ability to rise and form a storm. Most of the time, a storm will bubble up and rain itself out. But if there is enough shear — a change in wind direction with height — that storm can begin to twist, keeping its updraft rain-free, potentially maintaining its strength for hours. We call those supercell storms.

Surprise tornado outbreaks in Southern New England are virtually unheard of. After all, temperatures were in the 50s, and a moisture-starved atmosphere was present. While there was plenty of wind shear in Tuesday’s environment that we could see in the lead up, the atmosphere seemed largely starved of energy to support rising motion. Almost.

In the lowest 5,000 feet in the atmosphere, there was a lot of instability. even if a thin layer. That meant updrafts at the base of the clouds were sucking air in rapidly, even if that updraft didn’t extend very high upward in vertical extent.

In the Plains, most supercell thunderstorms tower to 50,000 feet or more. Tuesday’s barely reached 30,000 feet. But with surface air screaming upward into the cloud base, the storms didn’t have to climb all that high. The updrafts close to the ground were strong enough.

Why the concentration near Cape Cod?

Why was there such a concentration over spin-ups over the east end of the Cape Cod Canal? Knowing the local area and the meteorology, I hypothesize there are several reasons that made it Tuesday’s miniature Tornado Alley.

The first is the funneling effect of winds through the canal. Air blowing into Buzzards Bay from the southwest experiences a sort of “wind tunnel,” thanks to the cliffs on either side — particularly from the Bourne Bridge to the Sagamore Bridge. This may speed up winds at ground level, enhancing wind shear and boosting low-level rotation. (Although it should also be noted there was plentiful low-level rotation area-wide.)


A two-dimensional radar rendering of the second supercell to spawn a waterspout at the east end of the Cape Cod Canal on Tuesday at 6 p.m. shows that rotation is parked immediately over the canal. (GR2 adapted by Matthew Cappucci)

Friction also played a part. On either side of the canal, trees, vegetation and structures slow down the air. But with nothing impeding its flow, a narrow strip of uninterrupted wind can zip just above the water’s surface. That also helped speed up low-level winds.

The presence of Cape Cod Bay just a half mile to the east also probably added moisture to the air. That allows lifting condensation levels to drop. In other words, the cloud base lowers a little closer to the ground, making it easier for a funnel to snake its way down to the surface.


A three-dimensional radar rendering of the second supercell to spawn a waterspout at the east end of the Cape Cod Canal on Tuesday at 6 p.m. shows rotation parked immediately over the Canal. (GR2 adapted by Matthew Cappucci)

Water temperatures were instrumental as well. At the east end of the canal, the shallow water is some of the warmest in the region this time of year. Contrasted against the winterlike temperatures just a mile above the ground, the waters added extra instability and “lift” to the air. We see this over the Great Lakes in fall as well.

And finally, why two storms in two hours? A weak, stalled air mass boundary, or the effective warm front, was probably draped near the canal. This frontal zone allowed storms to train like rail cars on a train track and enhanced vorticity — spin energy — near the interface.

Not at all Octoberlike

The storms also dropped hail more than an inch deep in spots, coating the ground with pea-size ice pellets. Farther north in Maine, thunderstorms were accompanied by sleet, thanks to freezing air less than a mile up. The tip of Mount Washington, whose summit soars higher than any other around here, picked up 18 inches of snow.

Meanwhile, a flight leaving Manchester Regional Airport in New Hampshire en route to Orlando was forced to land in Connecticut after being struck by lightning. Southwest Airlines Flight 2515 safely touched down in Hartford at Bradley International Airport and took off again after a four-hour delay.

A.J. Waterman, a native to Massachusetts and broadcast meteorologist in Wisconsin, was visiting home for the World Series. “I was getting ready to go to Game 1 when I noticed storms popping up,” he wrote. “I instantly pulled up radar and was shocked to see the storms were rotating.”

Waterman quickly drove south, missing the Rhode Island storm and rendezvousing instead with the second tornadic supercell to strike the Canal. “A photo from the top of the Bourne Bridge was all that could be managed from the unusual October storm, but the tornado was there.”

Amid all the crazy weather, a bit of good news: the Red Sox managed to play the visiting L.A. Dodgers at Fenway without delay.