Another EF-1 Tornado in Connecticut

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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.

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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.

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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.

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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!

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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.

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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?

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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.

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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!

“Typical” Connecticut Severe Weather

While we all remember the events like July 1989, June 1995 or June 2011 severe weather events like the one yesterday on June 22nd are far more common. Marginal/modest factors came together to produce sporadic reports of large hail and wind damage. No significant severe weather was reported but we had an impressive cluster of storms nonetheless.

At the end of a 3-day heat wave, an approaching shortwave and weak cold front was the impetus for convective initiation. Don’t get too excited about this 00z June 23 500mb analysis! Weak height falls and DCVA created broad synoptic scale lift over southern New England – and was enough to break the cap that had stifled convection the previous two days.

Temperatures in the low 90s and dew points between 65 and 70 were enough to overcome the eroding cap and convection fired across the state after 1:00 p.m. Sea breeze boundaries, differential heating boundaries (thanks to advancing mid level cloud deck), and eventually outflow boundaries created a mish mash of thunderstorms across Connecticut. While it was easy to get overwhelmed by the shear (no pun intended) of storms the ones that produced severe weather were easy to pick out on radar. Everything behaved well!

Mid level winds remained weak (500mb flow about 30 knots) with 0-6km bulk shear values between 25 and 30 knots during the event. Even with only modest 500-700mb lapse rates MLCAPE values ranged from 1500-2000 j/kg – certainly enough to support severe convection. While most storms were of the ordinary cell variety there were two supercells that developed and several multi cell clusters that lead to a number of borderline severe wind and hail reports.

18z RUC Analysis Sounding HFD

No surprise the majority of the reported damage (and likely all the severe criteria hail and wind reports) came from supercells even though the environment looked somewhat meh for sueprcells. The first developed in the Catskills and tracked through Dutchess County, NY. As should be expected given unidirectional wind profile and straight hodographs the supercell split shortly after moving into Connecticut.

18z RUC Analysis HFD hodograph

While it wasn’t clear given marginal deep layer shear that supercells would develop the straight hodograph indicates that splitting supercells are favored with neither right or left favored from there (thanks Shabbs). Here is a 3d radar cross section of the supercell shortly it split over Sharon.

You can see a hook echo to the south associated with a low level mesocylcone and rear flank downdraft. The core of this storm was dropping some pretty significant hail as well near Cornwall Bridge with 70dbz up to 26,000ft and impressive three body scatter spikes (hail spikes) on ENX radar (not shown). Wind damage was reported in Kent south of the storm and that was likely due to 40-50 knot winds in the storm’s rear flank downdraft. In fact damage was widespread enough that Macedonia State Park and Kent Falls State Park were closed due to tree damage.

The right moving supercell died a quick death shortly after its RFD developed as low level shear was insufficient to keep the RFD from choking the storms updraft. The left moving supercell strengthened a bit as it moved toward Torrington.

Damage was widespread in Goshen, Torrington, and Harwinton and was likely due to RFD winds in some locations (particularly south) and a macroburst in other locations (particularly north) as the core of the supercell began to collapse.

ENX 0.5 degree base reflectivity and base velocity showing low level mesocyclone and hint of an RFD? Not shown is the elevated hail core of the storm descending as storm enters Torrington.

The second supercell of the day developed in Manchester and quickly split like the Litchfield County storm.  The left mover produced a macroburst in Tolland that was easy to see on radar as the core collapsed, while the right mover hung on for a while doing damage in Willimantic and Scotland before falling apart.

OKX 2.4degree base reflectivity (16-18kft over Tolland County) showing the 2 updrafts splitting over Manchester. The left mover moved well left of the previous storm motion and right mover jogged ESE.

The storm split occurred between 4:20 p.m. and 4:30 p.m. and by 4:42 p.m. you can see above two distinct updrafts both producing hail and wind damage. It appears that downbursts/macrobursts occurred in both storms moving in very different directions.

Every severe weather event is different but many around here have similarities. Weak mid level lapse rates and moisture-laden sounding (nothing says siggy severe like moist adiabatic, right?) gave us marginal CAPE and there was just enough deep layer shear to develop 2 supercells. It still amazes me how powerful doppler radar is and how we can analyze these storms so easily. During our severe weather coverage yesterday we were able to point out specific areas vulnerable for severe wind/hail damage and we nailed every single one (Kent, Sharon, Goshen, Torrington, Harwinton, Tolland, Windham, Scotland) with good lead time. Let’s hope the next one is so easy 🙂