Flash Flood Risk Growing In Vermont, And Rest Of The Northeast

A strong thunderstorm seen here approaching St. Albans,.
Vermont from the southeast, instead of the west like
we'd usually see from storms. This storm was part of 
an opening salvo of storms that is bringing a 
flood threat to southern Vermont through tomorrow 

 I was afraid this would happen. 

The flash flood risk is growing notably in parts of Vermont, and a large chunk of the Northeast. 

A flood watch is now in effect for central and southern Vermont. The areas under the watch can expect one to three inches of rain through tomorrow evening. That doesn't sound so bad, until you consider there could well be some streaks of three to five inch amounts in that zone. 

The flood risk has already started.

If you're in the southern half of Vermont - especially if you're in or near the Green Mountains, prepare for local areas of flash flooding anytime between now and during the day tomorrow. 

This weather setup reminds me a little of the way things arranged themselves for the big July flood of 2023,  That said, I don't want to give you a flareup of PTSD.  This weather pattern IS NOT as intense or as capable of producing widespread like it did in July, 2023,  But I expect at least some pockets of flood damage in the Green Mountain State. 

THE UPDATE

All this is based on weather data that came in late this morning and early afternoon. That data doesn't exactly paint a pretty picture. Rainfall will be heavier in many areas than we thought early this morning. 

 Early this afternoon, NOAA's Weather Prediction Center extended a moderate risk of flash flooding between now and tomorrow morning through eastern Pennsylvania, northern New Jersey, and southwestern New England into far southern Vermont. 

A moderate risk, level three out of four, almost guarantees at least some flash flooding. A thick moisture feed combining with the instability brought on by a pesky upper level low over the Northeast could produce as much as five inches of rain within six hours in some local areas within the moderate risk area. 

The slight risk of flash flooding, level 2 out of 4 risk level, now extends north almost to Route 2. There's a good chance of some instance of local flooding in central Vermont between now and tomorrow night, especially along the east slopes of the Green Mountains. 

A marginal risk, one out of four covers far northern Vermont for the chance of very isolated flooding. 

Thunderstorms blossomed rapidly along the western slopes of the Green Mountains early this afternoon. The last one to develop seemed to come out of almost nowhere in Franklin County in the mid-afternoon and it was strong enough to carry a severe thunderstorm warning. It also came from an unusual direction - from the southeast rather than the west they way storms usually do.

That motion is a clue that we're getting a lot of moisture off the Atlantic Ocean for the atmosphere to play with. 

The storms were moving right along at a brisk pace, so any one storm wouldn't drop much rain in a particular place. The trouble will come if and where multiple stores move over the same place over and over again.

I have noticed that downpours in far southern Vermont have been looking pretty persistent this afternoon, but so far, as of 4 p.m., there were not flood alerts in effect. But this is the place to watch through this evening, as these storms will feature the heaviest rain of this whole three-day rainy event.  

TONIGHT/TOMORROW

The developing area of low pressure heading toward New York and southern New England will set up a sort of fire hose of moisture moving southeast to northwest from southern New England through southern Vermont, then weakening as it moves further north into upper Vermont and the Adirondack. 

This set up will really soak the summits and eastern slopes of the southern and maybe central Green Mountains, That will keep the flood risk going through most of tomorrow. The rain might not be as heavy as the locally torrential downpours today, but the rain could easily be strong enough to keep the flood risk going, 

The flood risk will diminish as you go north toward the Canadian border

For now, storm totals look like they'll run three to five inches in far southern Vermont, with local amounts as high as six or seven inches especially in the mountains. So you can see why this weather system is risky. 

The central Green Mountains look to have one to three inches, with perhaps locally higher amounts.  Northwest Vermont should get maybe three quarters on an inch, give or take, again with locally higher amounts. 

The Northeast Kingdom will largely miss out, as forecasts stand now. Some places up there might receive only a quarter inch of rain. 

Meanwhile, most of southern New England is under a flood alert through tomorrow, 

CAVEATS/WHAT TO DO

As always, things could change one way or another overnight. Heavy storms like this can shift the heaviest rain a few miles in unexpected directions, which could affect who gets the worst of flooding, if any. 

So, if you live in southern Vermont, be ready for at least some localized flash floods. Much of this could happen after dark, and it's hard to see washouts and flooding ahead when you're driving at night. 

If you live in a flood prone area, especially where water can rush off of steep slopes, have a to-go bag ready, just in case. You might have to leave at the drop of a hat.  

Again, not everyone in southern Vermont will have a flash flood. But it's a big enough threat to stay on your toes through tomorrow. 

We've already had a few instances of flash flooding this summer in Vermont. Looks like this will be another. In our climate changed world, this kind of thing has become more likely than it was a few decades ago