Wednesday, September 11, 2013

Big, Severe Thunderstorms Likely In Parts Of Vermont This Afternoon, Evening


I'm more and more confident some severe thunderstorms will erupt this afternoon and evening in Vermont and surrounding states.

A severe thunderstorm watch has just been issued for all of Vermont and much of the rest of northern New England until 10 p.m. tonight.

Atmospheric conditions are such that it needs to get up to between 85 and 90 degrees this afternoon in Vermont and northern New York for updrafts to break through a layer of stable, warm air high above us.  Shortly after that happens the thunderstorms will begin in earnest

As of 2 p.m., it was 90 degrees in Burlington, Vermont and 93 in Plattsburgh, N.Y., so we're there.

From my perch in St. Albans, Vermont, I'm noticing thunderheads beginning to pile up in the distance, especially to my north and west.

The towering clouds are not rising straight up. They're tilted quite a bit toward the northeast. That, to me, indicates there are strong winds high above us, which will help severe thunderstorms develop. And some of those high winds will be brought down to the surface in the turbulence inside any thunderstorms that do form.

As I said this morning, not all of Vermont and surrounding states will get a severe thunderstorm this afternoon. It'll be hit and miss, with some towns getting blasted and others remaining relatively unscathed. It's hard to tell which town will get hit until the the thunderstorms form and we know which areas they're targeting.

A special weather statement just issued by the National Weather Service in Burlington says the most likely time for the strongest storms is between 5 p.m. today and midnight. I have no reason to dispute that assessment. It'll take a little time for the storms to get going.

Interestingly, there is still a slight chance of a brief, relatively weak tornado with this outbreak in northern New England. We associate tornadoes with flat, open areas, but the National Severe Storms Center says if any tornadoes do form, it is most likely in Vermont's hilly Northeast Kingdom and in the mountains of northern New Hampshire and western Maine.

Still, the threat of a twister is very low. Just a slight chance.

Stay tuned and keep an eye to the skies.


Contrary to predictions, no severe thunderstorms developed Tuesday in Vermont and surrounding states.
The forecasted big storms Tuesday didn't materialize.
There's still a risk of nasty storms today, like this
one in St. Albans back in July.  

As far as I can tell, at least two things gave us the breather:

A slow moving warm front didn't quite make it all the way through New York and New England until last night. That meant there was a layer of warm air over the top of cold air, and that prevents the big towering clouds of thunderstorms from forming.

An even bigger factor was the overcast. Sunshine heats the air right near the ground. The warm air, lighter than cooler air, rises. The rising air initiates the process in which thunderheads start to bubble upward. No sun Tuesday, so no rising air currents to speak of.

Today, Wednesday, is a different story. The warm front has passed, as anyone stepping outside can tell you. It's incredibly humid, even by mid-July standards, never mind September. The temperature is likely to hit 90 degrees in many spots in northern New England today.

Big thunderstorms thrive on heat and humidity, so there you go.

The sun is out, so we'll have those rising air currents. There's fast winds high above us, and the atmosphere is primed to host huge thunderstorms.

So there is the chance of severe thunderstorms today across the northern half of New York and the northern half of New England.

It seems like the closer you are to the Canadian border, the more likely a big storm will hit you. That's because there's a weather front in Quebec, and that could act as a trigger for storms that would then lumber across the border (Ignoring U.S. Border Patrol and Homeland Security in the process) and cause some problems in New York, Vermont, New Hampshire and Maine.

It was still unclear early Wednesday morning if there will be enough of a trigger to produce a lot of severe storms. Will the updrafts from the sunshine help cause storms? Is the front in Canada strong enough? Are there other hard-to-discern wind shifts that could get a storm going?

We think so, but it's not a sure bet.  My sense is there will be storms scattered around today. It'll be the typical hit and miss type of set up. A few towns get blasted by wind and hail and lightning, other towns go through the day without even a faint rumble of thunder.

So look to the skies. Some of us could easily get a storm with damaging winds and big time hail. My guess it won't start until 2 p.m. at the earliest, with the prime time for possible storms in the late afternoon and evening.

The National Severe Storms Center also has us in a risk for severe storms Thursday as a cold front comes and interacts with the humid air.
"Training thunderstorms", a line of storms going over
the same spot one after another, dumped enough rain
to wash out this Cambridge, Vermont road in May.  

There may well be some severe weather in the Northeast. But National Weather Service forecasters in Burlington are more worried about the rain Thursday's thunderstorms might bring.

Tomorrow's weather pattern favors "training thunderstorms" That's the dreaded situation where thunderstorms line up like box cars on a train track. Then the box cars, in this case thunderstorms, go over the same spot, one after another.

One thunderstorm with a downpour isn't a big deal. A whole bunch of downpours going over the same town, one after another like those box cars, can drop tremendous amounts of rain, and it becomes a really big deal. The situation can dump many inches of rain on a particular town,  causing a flash flood in the places unlucky enough to be hit by this type of "train"

You never can tell a day in advance where these trains will set up, if they do at all. So you'll need to pay attention to forecasts and possible flood alerts on Thursday.

After that, as promised, we return to our previously scheduled autumn in Vermont and surrounding states. It looks as if we'll get several days of somewhat chilly, largely sunny weather starting Saturday.

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