Weak spin-ups highlighted forecasting advances, lingering challenges
By Dakota Antelman, Managing Editor
MARLBOROUGH – The weak tornado that hit Marlborough Aug. 23 was barely noticeable through the National Weather Service’s (NWS) radar imagery tools, forecasters recently said.
The flood of eyewitness videos and photos of the tornado, though, then let those same forecasting teams catch subsequent spin-ups in Stow and Bolton more quickly than they otherwise might have, forecasters added.
“The observations that came in were very helpful,” said Science and Operations Officer Joe Dellicarpini.
Marlborough tornado one of six to hit Mass. in 15-day span
The National Weather Service’s Boston Office held a webinar on Sept. 14 breaking down a number of tornadoes that recently struck New England.
Those included two tornadoes in Clinton and Webster on Aug. 18, one tornado in Dennis on Sept. 2 as well as the three tornadoes that hit Central Massachusetts on Aug. 23.
All six tornadoes were relatively weak, causing no deaths, injuries or catastrophic damage. But they did still pose a threat, forecasters said.
The Marlborough tornado, packing 65-mile-per-hour winds, sent at least one tree onto a pair of parked cars and reportedly lofted tree branches and other debris into the air near Cedar Hill St. and the John Carroll Water Treatment Plant in town.
“It did go through a populated section of Marlborough,” Dellicarpini said.
Experts eye warning signs before Aug. 23 tornadoes
Forecasters began Aug. 23 watching signs of instability in the atmosphere as the remnants of Hurricane Henri spun over New York.
The NWS’ Storm Prediction Center in Oklahoma, which specializes in tornado prediction and forecasting, issued its morning outlook, predicting a slight chance of a tornado taking place in any given spot across much of eastern Massachusetts.
A few hours later, a scattered line of storms more than 30 miles ahead of the main disturbance rolled through the area.
Westborough’s John Bogaert watched those storms roll in “around noon” on Aug. 23.
Seated just outside his office off Route 9, he viewed what appeared to be funnel clouds blowing through Westborough and toward Marlborough.
“We watched these rotations go right over Route 9,” he recently told the Community Advocate.
Around the same time, Twitter user Adam Salmon shot multiple videos mere feet from the Marlborough tornado, which touched down at 11:40 a.m. according to the NWS. His footage showed swirling clouds above the industrial buildings along Cedar Hill St.
A few moments later, around 12:30 p.m., photographer Tami White hovered her drone high over the Ft. Meadow Reservoir in Marlborough. She shot video for roughly 30 minutes, capturing multiple funnel clouds forming and dissipating in the area.
The Marlborough tornado had already lifted and dissipated by the time White was airborne.
The Bolton tornado, though, touched down just at 12:30 p.m., according to the NWS, while the Stow tornado spun its brief path past Stow Police Headquarters at 1:10 p.m.
As community members posted countless other photos and videos to social media, forecasters also took notice.
Meteorologists struggle to identify Marlborough tornado through radar
Conditions had favored tornado formation. But the individual cluster of storms in question on Aug. 23 gave experts little specific indication that those conditions had actually allowed a tornado to touch down, Dellicarpini said on Sept. 14.
Radar imaging didn’t show the signature “hook” that meteorologists use to help identify a tornado in more traditional supercell thunderstorm situations.
A tool measuring wind speed and wind direction did detect rotation around Marlborough. But that system was only estimated to be spinning 14.5 knots, or 16.7 miles per hour just as Marlborough’s EF-0, 65-mile-per-hour, tornado officially touched down.
“That wouldn’t raise many eyebrows at all,” Dellicarpini said as he showed archived radar images to webinar viewers on Sept. 14.
NWS issues warnings before additional tornadoes
The NWS did not issue its tornado warning for Marlborough and its surrounding areas until after the tornado dissipated.
As storms rolled north into Hudson, Stow and Bolton, though, they were able to give more warning.
A tornado warning was in place at 12:30 p.m. when the day’s second tornado touched down in Bolton. The same was true at 1:10 p.m. when the third tornado touched down in Stow, Dellicarpini noted.
“Normally we wouldn’t expect that to really do anything,” he said of the conditions back in Marlborough. “So, the observations that came in were very helpful.
“[Forecasters] can correlate ‘Oh, I’m seeing the same signal up towards Stow’ and they issued the warning on that,” he continued.
“They were on it,” Dellicarpini said, speaking to the work of NWS forecasters. “… [It was] a tough situation but they did a pretty good job and warned on two out of the three [tornados].”
Experts address perceived increase in tornado frequency
Dellicarpini and meteorologist Rodney Chai fielded a simple question on Sept. 14 – Why are we getting so many tornadoes?
Massachusetts saw 33 tornados between 1980 and 1999. That number climbed slightly to 36 tornadoes between 2000 and 2019 according to the National Oceanic and Atmospheric Administration.
Within that, the state has experienced particularly busy years of late, recording seven tornadoes in 2018.
Six more tornadoes in less than a month this year have, in turn, made 2018 and 2021 the busiest and second busiest years of tornado activity in the state since 1997, when eight tornadoes touched down.
There could be multiple factors driving any perceived increase in tornado occurrences Chai and Dellicarpini said.
Climate change may be creating more instability in the atmosphere.
Forecasting technology has also improved, giving meteorologists better tools to break down thunderstorms and detect rotation in events that might otherwise be missed, the two explained.
Then, there’s social media.
“You give us so much information either through social media or you call in with information,” Chai told members of the public during the Sept. 14 webinar.
‘We’ve come a long way’
Experts say they “empathize” with the shock at what has, for some, seemed like a line of tornado warnings and confirmed tornadoes this summer.
Likewise, they said, the Aug. 23 events, in particular, underscore the difficulties of actually predicting, warning on and documenting what are often erratic tornado-producing storms.
“We don’t want to be overzealous in issuing the warnings…but also, at the same time, you need to know when to pull the trigger,” Chai said of the warning process.
In a field where, Dellicarpini said, forecasters aim to accurately warn on 70 percent of tornadoes while limiting false alarms to 60 percent of total warnings, the response on Aug. 23 was generally successful.
“We’ve come a long way,” Dellicarpini said. “[We] used to be worse.”