Isolated Tornadoes Possible 7/15/14

Ahead of an approaching cold front, strong to severe thunderstorms should develop Tuesday afternoon and continue into at least the early evening hours.

The greatest threats will be damaging winds and flash flooding from New Jersey up into the Hudson Valley, northwestern Connecticut and much of central and western Massachusetts. There is an isolated tornado threat and if I had to put numbers down, I would say that the entire region mentioned above could see between 1 and 3 tornadoes.

While there is some decent shear moving into the area, instability is a bit more patchy due to some lingering cloud-cover. Usually you also like to see stronger helicity values than those that are in place today for tornadoes, but there is still enough for at least an elevated tornado threat. Surface winds are somewhat backed out of the south across Connecticut, although winds aloft are out of the southwest. For the greatest tornado threat, you’d like to see 90-120 degrees or more of directional shear, but here we’re talking about maybe 45-60 degrees or so.

Stay tuned on Twitter for more updates @danburyweather (forecast and Connecticut specific updates) and @stormchaserQ if I’m out in the field chasing storms and for more technical thoughts.

Again, this is not a “classic” tornado setup and contrary to what some have been saying, the threat is actually on the low end of the spectrum using a tornado index I have developed. I cherry-picked the most significant severe weather parameters forecast (happens to be the Hudson Valley) and the result was just a 1.7 out of 5. The climatological mean for tornadoes in the area is 2.06, so while the value here would support weak/brief tornadoes, this is most likely not going to be a tornado outbreak.