Tuesday, September 10, 2013

Severe Weather Threat To Last Three Days In Vermont


I think the chances of severe thunderstorms this afternoon and evening have diminished somewhat. the National Severe Storms Center says so, as does the National Weather Service in South Burlington.

Their logic is too much warm air is moving in aloft, that would "cap" the development of storms. By that I mean it will be harder for the towering clouds of thunderstorms to form today than first thought.

Also there's quite a bit of cloudiness lingering behind this morning's rain. The clouds will block sunshine, which would otherwise heat the atmosphere and encourage thunderstorms to form.

Still, there might be a few pop up severe storms here and there across northern New York and New England today and this evening. I just don't think there will be a huge number of such storms.


I don't think I've ever seen anything like this: There's a chance of severe thunderstorms in Vermont for three days in a row, starting today.
A severe thunderstorm over St. Albans Bay, Vermont
in July. Similar scenes are quite possible in Vermont
and surrounding states today, Wednesday and Thursday.  

Severe weather is fairly rare in September. Three days in a row is pretty wild for this time of year.

Let's break it down: First, today: 

A cluster of showers and thunderstorms was moving through northern New York, Vermont and into New Hampshire Tuesday morning. While there are some downpours and lightning strikes with this, none of the weather is severe.

Once the cluster of storms goes by noon, you'll notice it abruptly turning humid. That will be one ingredient for possible severe storms later this afternoon.

The other ingredients are rising pockets of air, high upper level winds and something called shear. That's when winds change directions as you rise up through the atmosphere.

Those ingredients combined can set off lines of severe storms or supercells, the long lasting, giant thunderstorms that can produce tornadoes in some instances.

Working against the chances of severe storms today is this morning's rain. It tends to stabilize the atmosphere somewhat. Plus, a layer of warm air way up above us could put a "cap" on rising air currents, and that might discourage thunderstorms.

Still, I, and most other forecasters,  think some storms will get going in northern New York and northern New England today, and some of those might get severe, with strong winds, hail, and maybe even a brief, isolated tornado somwhere in this region.

Not everyone will get hit, but keep an eye to the skies later this afternoon and this evening. Things could get nasty.

Then we get into Wednesday.

On Wednesday it's going to be strangely hot and humid for mid-September. Temperatures could get up to 90 degrees in cities like Burlington, Vermont and Albany, New York. (The record high Wednesday in Burlington is 95 degrees. I don't think it will get that hot)

It'll be oppressively humid, on par with some of the most humid weather we've had all summer.

All that heat and humidity, along with an atmosphere that will continue to favor strong updrafts and changing wind directions, could set off more severe thunderstorms in a zone from northern New York through the northern half of Vermont,  northern New Hampshire, and into western Maine

The threat will be roughly the same as today: Not everyone will get hit, but some areas could get damaging winds, big hail, and maybe even a brief tornado. The risk of bad storms is greatest in the afternoon and evening.

One more day, Thursday.

We'll wake up Thursday morning to another oppressively humid morning. A cold front will be coming at us from the west.

The timing of the cold front will determine who has the biggest risk of severe storms. If it's a little fast, New York and Vermont could just get heavy rain with thunderstorms while the high winds, hail and slight tornado risk are more to the south and east.

If the front is slower, then New York and Vermont fall under the risk.

The front goes by later Thursday, and it's back to autumn and no severe storms by Friday.

This three day run of potentially hazardous weather in the Northeast is really odd for this time of year, as I've said. But severe weather isn't unheard of in the fall.

Way back in 1845, an incredibly large, long lasting tornado formed near Lake Ontario and traveled 200 miles across the Adirondacks, holding together despite the mountains, finally dissipating near South Burlington, Vermont.

In September, 1821, several damaging tornadoes hit Vermont and New Hampshire. 

More recently, a large tornado killed three people and caused major damage in 1979 around Windsor Locks, Connecticut. 

And last year, on September 8, all of Vermont was under a tornado watch, though no tornadoes are known to have developed in that outbreak of severe weather.  Here's a video of the storm I took last September 8 in Charlotte, Vermont. No tornado, but pretty stormy:

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