The F4 tornado that hit Poquonock, Windsor Locks, and Suffield on October 3, 1979 is one of the most unusual tornadoes in New England history. Strong and violent tornadoes in Connecticut and Massachusetts are unusual but they’re not unheard of. The 1979 tornado occurred in a very strange weather pattern that is unlike any other big New England tornado (1953, 1989, 1973, 2011, etc.). The extraordinary and highly unusual circumstances that lead to the Windsor Locks tornado make the tornado one of the most bizarre in New England history.
A strong disturbance in the upper levels of the atmosphere raced northeast toward Connecticut on October 3, 1979. The closed low that was ejected toward New England by a digging trough in the midwest was in the process of opening up and triggered violent thunderstorms across the northeast. The upper level wind flow was southerly over New England ahead of the low compared to the westerly or northwesterly flow that almost always occurs during high-end New England severe weather events.
Climatologically, October tornadoes are quite rare. Most Connecticut tornadoes occur during June, July, and August with very few occurring in October. The time of year is just another factor that made the storm so unusual.
As the upper level disturbance moved east severe weather occurred over Pennsylvania and New Jersey in the morning and then the violent tornado north of Hartford in the afternoon.
According to Riley and Bosart (1987) the radar imagery indicates that the storm may have been a left moving supercell that became tornadic when interacting with a warm front located near a triple point at BDL. At 18z, prior to the tornado, the suface analysis below shows the surface low just north of Danbury with easterly winds at BDL. You can see that before the supercell approached Bradley in the second image below that the winds were easterly all day while winds to the south of the front were from the south.
The weather pattern that lead to this tornado is certainly not a classic setup for a northeast tornado. Riley and Bosart argued in their 1987 paper that the instability was maximized in the Connecticut River Valley with a channeled southerly flow coming up the Valley from the Atlantic Ocean and Long Island Sound that transported warm, moist, and unstable air in the boundary layer up from relatively warm waters. The combination of instability, strong lift from the approaching upper level disturbance, and extreme wind shear near the warm front draped over BDL was enough to produce a short-lived, isolated, and violent tornado.
I can’t think of another weather pattern like this that has produced high-end severe weather in this part of the country. To this day the 1979 Windsor Locks tornado is the 8th costliest tornado to strike the United States (the damage in 3 towns amounted to an adjusted 700 million dollars). The 11.3 mile long tornado was 1400 yards wide at its widest point and is likely the strongest tornado to hit Connecticut in the last 100 years. Portions of an entire subdivision in Poquonock were flattened and 3 died in the storm and 500 were injured.