"The Curious Case" is a series of articles taking deep dives into some of New England's most unusual weather events and other occurrences.
Tornadoes in New England aren't quite as rare as some may think. Every summer, a handful of tornadoes touch down across the region. Since official tornado records began in 1950, over 600 tornadoes have been seen in New England. Massachusetts has experienced 200 of these tornadoes. What is exceedingly rare are for tornadoes to be seen in the winter.
Of Massachusetts' 200 tornadoes, only 4 have occurred in meteorological winter. The first came in 1951 with the second coming in 1956. It would be another 61 years before another winter tornado would strike the region. These would represent the first February tornadoes on record in Massachusetts.
THE SET-UP
The main driver of this winter severe thunderstorm outbreak was a spring-like area of low pressure rotating out of the Great Lakes region. On February 25th, this area of low pressure lifted a warm front across New England ahead of its arrival. Farther west, a line of thunderstorms developed along the system's cold front. This system was rather similar to an Alberta Clipper, a storm that would usually bring New England a quick hit of snow. So, the question is why in the world this storm created tornadic thunderstorms in New England rather than a blob of snow.
First and foremost, February 25th was the third day of record shattering winter heat. Widespread temperatures well into the 60s were observed on February 25th across New England. The day before saw a handful of 70+° readings. These temperatures are a good 30-40° above average for late February, so any thought of snowfall was clearly off the table. With such warm temperatures preceding the storm, the system's warm front created a warm sector more akin to what would be seen in the warmer months. Dew points shot up to the 50s.
Dew points in the 50s and CAPE values (a measure of instability) of around 100 joules/kilogram were observed with the storms, both of which are not overly favorable readings for severe thunderstorm development. In the winter, this is generally considered elevated, but still not enough to be too concerned about severe storms.
Helping to get the lift needed for storms in this marginal set up was a pair of strong upper-level jet streaks (an area of stronger winds within the jet stream) over the northeast and Mid-Atlantic. The positioning of the jet streaks placed the northeast in a favorable area for strong lift, helping to get the squall line going in what would otherwise have been poor conditions for this to have happened.
Below: A diagram of quadrants within a jet streak. The northeast was placed within both the right entrance and left exit regions of the two jet streaks, which helped to greatly increase lift (upward motion shown on the graphic):
Everything described above helped ignite a line of severe storms in the winter (which is already a highly unusual occurrence). With that said, more needs to line up in New England to produce winter tornadoes. The final major piece of the puzzle was the fact that the environment was strongly sheared. Shear is the main factor for rotation and tornadic supercells to develop. Shear values close to 75-100 knots were observed in parts of the region. For comparison, the June 9, 1953 New England tornado outbreak saw shear values up to 100 knots. This outbreak produced the strongest tornado in New England history.
While truly violent tornadoes were basically off the table given the other meager ingredients, the extremely high shear helped overcome the low humidity (by summer standards) and meager instability. The bulk of severe weather was expected to New England's west on this day. This was mainly due to the fact that the squall line would not arrive in New England until the evening, when the meager instability would be waning even more. This put western New England in the bull's eye for the storms.
Below: Storm Prediction Center severe thunderstorm risk for February 25, 2017:
THE TORNADOES
With everything in place, all that was left was for a rotating supercell to send a funnel cloud to the ground. At 7:18pm, a tornado very briefly touched down in the town of Goshen. The tornado lifted off the ground for several miles before touching down a second time in Conway, where it tore a 5 mile path from 7:20 to 7:25pm. Maximum winds of 100-110mph were observed, placing this tornado as a very high end EF1 (EF2 strength begins at 111mph).
In Conway, a very sharp gradient in heavy damage versus no damage was observed by the National Weather Service. After causing severe tree and power line damage in a heavily forested part of the town, the tornado moved into the downtown area. The National Weather Service described the damage as follows:
"In the area just to the southeast of the town hall, there were several houses that were severely damaged on Whately Road. Roofs were blown off, with some metal wrapped around middle and upper portions of trees. In one case, the side walls of a house were missing with the interior of the house exposed. On Hill View Road there was a large barn that was collapsed. Numerous trees and power lines were down. One injury occurred when a tree landed on a house just northeast of there, on South Deerfield Road (Route 116). That was approximately where the visible damage path ended."
Several local residents noted hearing the distinct roaring sound, often compared to a freight train, before the tornado hit. These residents were aware of what a tornado sounded like and sought shelter in their basements. Thankfully, no one was killed during what was a very unexpected and intense weather event for the town. Not many in New England ever really expect to have to shelter from a tornado any time of year, but to have a rather strong one rip through in the dark during winter is extraordinary.
Severe thunderstorms and tornadoes were not limited to New England. As stated before, the bulk of severe weather was expected to hit to the west of New England. The strongest tornado of the day was an EF2, which touched down near Scranton, Pennsylvania in the afternoon. Wind and tornado damage reports stretched from New Hampshire to North Carolina.
Below: Storm reports from February 25, 2017:
PRECEDENT
It's not unusual to see spring-like storm systems forming by late-February for the east coast. The threat of severe storms and tornadoes from these systems are often pinned to the deep south and occasionally move northward to the Ohio Valley. A total of four tornadoes touched down on this day; the two in Massachusetts (since the twister lifted off the ground, the Goshen and Conway tornadoes are counted as two instead of one), one in Maryland and one in Pennsylvania. This was Pennsylvania's fifth February tornado on record.
It is exceedingly rare for a tornado threat to push this far north and east when winter is still in full swing. There are, on occasion, severe thunderstorm events in winter for the northeast. Just one year before this, an outbreak of thunderstorms occurred, bringing heavy rain and isolated severe weather to the northeast. This event was centered farther south with only the very northern reaches pushing into the northeast. Two tornadoes touched down in Pennsylvania during this event.
Another severe weather event took place on February 17th, 2006, with widespread wind damage occurring. Most of this activity was limited to New York, however. On December 1st, 2006, widespread severe storm wind damage occurred throughout New England. Three tornadoes touched down in Pennsylvania on this day. None of these events (2016 & both 2006 events) produced tornadoes in New England.
Below: Storm reports from December 1, 2006:
CONCLUSION
It really is quite remarkable to see not just a thunderstorm, not just a severe thunderstorm, but a tornadic supercell in New England in winter. And not just a tornadic supercell at that, but a high end EF1 that caused heavy damage.
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