When Nick Stanczyc posted this picture on Instagram someone forwarded it to me within moments. I couldn’t believe it! The classic looking tornado was just about a half mile away from the intersection of Rt 30 and Rt 31 in Mansfield near Storrs.
On the 24th anniversary of one of the state’s most violent tornado outbreaks we got hit again – but by a much weaker storm. The first sign of trouble came around 1:30 when a rather unimpressive thunderstorm began to show signs of rotation over Watertown, Thomaston, and Plymouth.
For a period of time while near Route 8 there was a Delta-V of 40 knots on adjacent gates in the storm’s radial velocity (i.e. 20 knots inbound and 20 knots outbound) about 4,000 ft above the ground. In addition, the reflectivity signature indicated a small hook echo or appendage associated with the storm. Unlike the July 1st storm (which was a low topped supercell) the rotation was seen through a large portion of the storm from about 4,000 ft at the lowest radar sample to 22,000 ft.
The 17z RAP analysis sounding shows an environment that was capable of producing rotating storms. The environment was quite unstable with surface based CAPE values exceeding 2000 j/kg. In addition there was fairly impressive directional and speed shear through the lowest 3km of the atmosphere. Because of this there was fairly sharp curvature of the hodograph between 1 and 2km above the ground. It’s no surprise that a somewhat discrete cell ahead of the main cluster was able to take on supercellular characteristics.
While the radar presentation for the storm in Watertown was arguably the most impressive of the day the storm did not produce damage and did not produce a tornado. The likely reason why is that there was little 0-1km shear – the bulk of the shear was above that level. The height of the lifted condensation level or LCL (think of this as the cloud base) was around 800 meters. While low, this was not as low as we saw during the July 1st tornadoes or the subsequent storms in northeastern Connecticut (where LCLs were near 300 meters!)
The overall synoptic environment was characterized by a deep trough in the Great Lakes with a shortwave rotating underneath it through New York and New England. QG forcing for ascent was greatest ahead of this with fairly widespread shower and thunderstorm coverage.
Shortly after 5 p.m. – 2 supercells had developed in Connecticut. One produced some damage near Tolland and another in Coventry and Mansfield. Here’s the 21z sounding from the RAP analysis at the Windham Airport. Most of the shear is located in the 0-1km layer with a helicity of 111 m2/s2. There is about 1100 j/kg of sb CAPE and LCL heights are VERY low – about 300 meters!
The storm in Tolland shortly after 4 was totally unimpressive on radar. There’s some signs of a weak low level mesocyclone but the storm itself was about as exciting on radar as a snow shower. Even so, it was apparently able to produce some damage in parts of Tolland just west of the Green as it crossed I-84. This damage was ruled to be from straight line winds and not a tornado with trees knocked down in a southwest to northeast fashion along the storm’s path.
The most likely “cause” for the wind damage in Tolland wasn’t a classic microburst but rather a damaging rear flank downdraft that produced a corridor of >50 knot southwesterly winds along the storm’s path. This would make sense given the fact many people saw a funnel cloud though there was no conclusive evidence of a touchdown.
As the storm moved northeast the mesocylone remained and even strengthened a bit out toward Willington and Union. It’s unclear to me what happened shortly after 5 p.m. The first mesocylone over Tolland weakened as it crossed into Stafford and Willington while a second, and stronger, mesocyclone develop on the southeast flank over Willington and then moving into Ashford and Union. This turned into the more powerful mesocyclone and peaked with a low level delta-V of about 40 knots and a tornado warning from the folks in Taunton. Whether this was simply the mesocyclone “cycling” or if this was a splitting supercell it’s hard to say based on the radar data I’m looking at now. Anyone have any ideas?
The most impressive storm of the late afternoon developed shortly after 5 p.m. to the southwest of the Willington/Union storm. Rotation was evident as the storm left Glastonbury and it strengthened in Hebron and Andover. The storm produced an EF-1 tornado from Andover to Mansfield with the worst damage concentrated in an area of Coventry near Coventry Lake.
Given the super low LCLs and enough turning in the lowest kilometer of the atmosphere it’s not a surprise that this storm produced.
Given the advances in doppler radar (super resolution!) and the proliferation of smart phones with cameras and social media it’s not a surprise we’re hearing a lot more about these tornadoes than we have in the past. Tornadoes are nothing new here in Connecticut and even though it seems we’ve been getting an unusual amount of late this is really the way it has always been. The state is vulnerable to tornadoes and while most of our tornadoes are weak (EF0 or EF1) we have a long history of significant and violent tornadoes. Being able to hear about damage within moments and get pictures of the tornado shortly after touchdown thanks to everyone with an iPhone or Droid allows us to cover tornadoes and severe weather much more effectively.
While it’s been a busy year for tornadoes in Connecticut – to be honest – we’ve just been sort of unlucky. Marginal setups have been able to produce spinners. Hopefully yesterday’s was the last tornado of the year!