Friday, June 30, 2017

Vermont, New York Get Surprise Downpours, Flood Threat Dramatically Worsens

Chaos in Barre, Vermont after a May, 2011 flash flood.
There's some risk we could see scenes like this again this weekend.
Much more rain fell across northern New York and the northern half of Vermont overnight, and this sets the stage for a real flood threat.

The threat is even higher than I had been expecting earlier this week.

Last night's torrential rains, amounted to two to three inches, locally even a little more from the St. Lawrence Valley of New York, across Lake Champlain and the northern half of Vermont.

Burlington got 2.16 inches of rain and Colchester piled up 2.71 inches.

By the way, June rainfall in Burlington has so far amounted to 6.79 inches. If we don't get a drop of rain today, it'll still be the seventh wettest June on record.

Flood warnings were issued across a stripe of northern Vermont, along and roughly 30 miles either side of a line from Burlington to a little south of St. Johnsbury.

There's been no major flooding in that zone, but there is high water, washouts and that kind of thing.

Mainstem rivers are already getting into the act, too. There's a flood warning for the Winooski River at Waterbury. Today's flooding won't be as bad as during Tropical Storm Irene, when the Winooski flooded most of downtown Waterbury.

But low spots, and low roads are going to go underwater. Flooding will cover fields and damage crops downstream to Richmond, and possibly all the way down to the famed vegetable farms in Burlington's Intervale.

The rain was temporarily waning early this morning and the flood warnings will have probably been dropped, at least for awhile across northern Vermont by the time you read this. With the exception of the Winooski River flood warning, which will probably remain in effect most of the day, even if we don't get much more rain.

However, this flood event is only just beginning.

A flash flood watch is up across northern New York, the northern half of Vermont, northern New Hampshire and western Maine through Saturday night.

The warm front that caused the torrential rains last night is lifting toward Quebec and we'll get firmly entrenched in the warm, very humid air today.

Disturbances riding along a front to our west will fire up plenty of showers and thunderstorms this afternoon and evening, and some will of course have torrential rain.  Even as I write this at 7 a.m. Friday, heavy downpours were lurking in western New York, heading east.

Here's how high the risk is: It would only take about an inch of rain in an hour to cause a flash flood. Some of the thunderstorms today and even more numerous ones Saturday and Saturday night could easily drop two inches of rain in an hour.
Flash flooding in Richmond,  Vermont in June, 2013. This
kind of thing could easily happen again today, and
especially Saturday in Vermont. 

And some locations that are unlucky enough to get repeated storms could get three to five inches of rain between now and Saturday night.

We get flash flood watches fairly often, but this to me is the most precarious situation since the big spring and summer floods of 2011.

Some of today's storms could also be severe, with strong gusty winds. NOAA's Storm Prediction Center has Vermont in part of a broad zone of a slight severe storm risk today.

The storms will subside tonight, but there's still a chance of locally heavy downpours overnight.

For what it's worth, one weather model has a band of heavy rain lingering for several hours across northern Vermont this evening. That might or might not actually happen, but it's something to watch.

Saturday afternoon and night is looking even more dangerous. The cold front to our west will be closer, and the thunderstorms will be much more numerous Saturday than they will be today.

Even worse, the air will be even more humid than today, providing the fuel for even more torrential rains. And some of those storms could be severe, with gusty winds.

Not only is flash flooding a threat, but some of the bigger rivers in the North Country could flood. We already mentioned today's flood warning on the Winooski.

I wouldn't be surprised if the Winooski flooded again by Saturday, along with other rivers like the Ausable in New York, and Vermont's Lamoille, Mississquoi and Mad rivers. This all depends, of course, on how widespread and heavy the rain is.

So heads up. It's going to be a rough weekend. The threat of flooding is pretty damn high. We could get lucky and not get so many storms, but I'm not holding my breath. This could be one for the record books.

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