The Almost Tornado Day

Yesterday was a busy day in the weather office! A cluster of storms straddling the Connecticut/Massachusetts border featured varying amounts of rotation and given the environment we were concerned about tornadoes.


The good news is – no tornadoes developed! The environment appeared prime for tornadoes. Around 3 p.m. we had relatively strong low level shear with 0-3km helicity >200 m2/s2. The storm motion off this hodograph is just to the south of due east at about 12 m/s.

The storms that developed were moving to the northeast or east-northeast across Connecticut. My buddy Chris Legro at the National Weather Service in Gray, ME theorized that this could indicate that these storms may have not been rooted at the surface for at least some of their lifetime given their storm motion.

In Woodstock, storm chase Joseph Berger grabbed this shot of a wall cloud over the Woodstock Fairground. Video making the rounds on Facebook shows a rotating wall cloud with some scud hanging around underneath.  The video above from Joseph Berger shows a bit of rotation and a likely Woodstock nearby in Woodstock. This thing was close to dropping a tornado.


Here we have about 45 knots of low level delta V (LLDV) – though it is a bit broad. Keep in mind the average LLDV for northeast tornadoes in recent years of 50 knots LLDV. Had it been a bit tighter maybe we would have had a tornado?

Before the Woodstock wall cloud we had an even more dramatic jump in low level rotation – with 67 knots of LLDV that lasted for only one scan over Eastford and Pomfret.


The couplet appears legit – though those outbounds look a bit suspicious. Regardless, even tossing some of the higher values we’re close to 50 knots of LLDV which is concerning.

A second storm had a pretty interesting look over Simsbury as well. The radar from Boston was picking up ~45 knots of LLDV but the radar from Long Island was actually sampling the storm 2,000+ feet lower with only marginal rotation. A good reminder to use multiple radars!

kbox_20160816_1906_NROT_0.5 kokx_20160816_1905_BR_0.5

So what happened? I think these storms may have no been completely surface based. The storm in Woodstock/Pomfret/Eastford got awfully close to dropping a spinner but couldn’t quite get it done. While 0-3km shear was impressive winds were relatively weak in the lowest 1km of the atmosphere. That may have played a role. Several of the storms we saw had better mesocyclones 5-10kft up than they did at the lowest elevations.

Later in the afternoon and evening the setup looked awfully juiced for severe storms. Long, curved hodographs and plenty of instability and it went to waste! This HRRR forecast sounding for Hartford valid yesterday evening shows fairly substantial convective inhibition or CIN. In the absence of strong forcing we were unable to eliminate this cap for surface-based storms.


These events are always fascinating and always challenging to forecast. In retrospect there’s probably not a lot we could have done differently – we were pretty lucky we didn’t have 1 or 2 tornadoes in the state yesterday afternoon as we were really close!

1 thought on “The Almost Tornado Day”

  1. Ryan, I live in Wethersfield. It has seemed, for a while now, that we get spared the harshest weather as it moves through the state. Whether it’s winter or summer. Is there a reason for that? Or are we just lucky?

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