Saturday, July 1, 2017

Today, Vermont's Flash Flood Risk Peaks. Severe Weather, Too

The swollen Winooski River raged through Essex Junction
Vermont on Friday. With rivers running high and soil
saturated, as little as an inch of rain today could set off
flash flooding in Vermont. 

Things in the weather department aren't progressing as planned as of noon in Vermont, and that could be both a good or a bad thing.

Or both.

As of noon, a large area of rain is moving out of New York into the northern two thirds of Vermont.

I'll give you the potentially good news about this first.

The big area of clouds and rain is stabilizing the atmosphere, which could well end up reducing the threat of severe storms.

The threat is still definitely from southern Vermont and points south, but things are more iffy in the north.

Atmospheric conditions are still potentially conducive to severe storms, and if we get a burst of sun after this rain goes by, we could still have some severe weather. It's just less certain now.

Interestingly, the Storm Prediction Center has the best chances of severe storms and tornadoes across eastern New York near Albany, central and southern Vermont and western New Hampshire

And here's the bad news, or at least worse than the news above:

This big area of rain has pockets of heavier precipitation within it, and a lot of it is moving into the Champlain Valley and northern and central Vermont.

These are the areas most prone to flash flooding today, because those are the areas that got totally dumped on with rain Thursday night and Friday morning.

Some storms in Rutland and Windsor counties already dropped over an inch of rain in places this morning. However, those storms hit an area that got less rain the other night, so so far, no flooding to speak of.

As of noon, I was especially worried about the southern end of this big area of rain moving in. This southern end has the heaviest rain, and a band of it extends well into New York State. This area of heavy rain looks to be now entering Vermont around Addison County, and will move northeastward to say, Montpelier.

If this area of heavier rain holds together as it makes its way into north central Vermont, there could be some real flash flood issues in places like eastern Chittenden County, Washington, Orange, Caledonia and Lamoille counties perhaps.

We'll keep an eye on it.


Well, if you like active weather in Vermont, today might be your day.

All kinds of potential hazards are in play for the Green Mountain State today. The first and foremost being the flash flood risk.

We might also get some severe thunderstorms, very damaging winds, perhaps a supercell or two, and there's even a very, very, very slight chance of a tornado. Could happen, though.

Of course, as we've been watching for days, the flash flooding is the biggest issue today.

Rainfall on Friday wasn't all that heavy across northern Vermont. The heavy stuff went south. (There ewas actually a tornado in central New York west of Utica yesterday. And there was one severe thunderstorm report in Vermont, as trees fell during a storm in Salisbury, in Addison County.)

That the heavy weather largely missed Vermont yesterday doesn't matter, though.

The soil is still saturated, rivers are still running high, and all it would take is perhaps an inch of rain in an hour to set off local flash floods. Any of the thunderstorms today could do that and more.

NOAA's Weather Prediction Center has northeastern New York, Vermont, northern New Hampshire and western Maine in a moderate risk zone for excessive rain. Moderate risk from this outfit is pretty high, which means they have a fair amount of confidence in the risk of too much rain too fast.

Needless to say, a flash flood watch is still in effect for northern New York, the northern half of Vermont, northern New Hampshire and western Maine into this evening.

Meanwhile, NOAA's Storm Prediction Center has us in the slight risk zone for severe thunderstorms. Damaging downburst wind gusts are the biggest threat today, but as I said, we can't rule out a couple rotating supercell thunderstorms, which, if perfect conditions are met, could spin up a brief tornado in eastern New York or Vermont.

Yesterday, a batch of rain moving in the morning and early afternoon helped squash most of the torrential rains and thunderstorms that would have wanted to get going later in the afternoon and evening across northern Vermont.

Today, a similar batch of rain was moving in as of 7:30 a.m. That could tamp down things a little, but don't count on it. The dynamics in the atmosphere, the upper level winds and such are different than yesterday, and more conducive toward strong thunderstorms and torrential downpours.

Plus a lot of that steady rain this morning was moving northeastward into Quebec and not as much into New England.

As of 7:30 a.m. strong thunderstorms had already developed in central and western New York and this stuff was moving northeast, roughly toward Vermont. I noticed there was already a severe thunderstorm warning up for an area just east of Utica, New York as of 7:30 a.m.

The thinking is the activity that was in central New York this morning will continue to strengthen along a weak trough line ahead of a cold front. The trough line is sort of a pre-cold front cold front.

All these things do is focus thunderstorms and provide lift to make them stronger.

The National Weather Service in South Burlington is thinking the thunderstorms with this trough will make it to the eastern Adirondacks by late morning, then swing into Vermont during the early and middle parts of the afternoon.

That's when the crap hits the fan, so to speak. That's when we're at the biggest risk of severe thunderstorms, damaging winds and of course those flash floods.

As the actual cold front approaches this evening, we could get into another round of heavy showers and thunderstorms. This second batch would probably be not as bad as what comes through earlier in the afternoon but the evening stuff could still contain a few strong thunderstorms and torrential downpours

By the way, Sunday is looking way better, with quite a bit of sun, a very slight chance of an afternoon shower or thunderstorms, definitely somewhat lower humidity and temperatures near 80 degrees.

No comments:

Post a Comment