Interesting Weather Sunday Afternoon In Vermont Mountains

Towering clouds, soon to be showers and storms begin to 
erupt early this afternoon well east of St. Albans over the
Green Mountains. Storms will tend to sit over the 
mountains the rest of the day while the Champlain Valley
looks like it will mostly stay sunny and hot and humid

 I'm sure you all noticed, but it's pretty stuffy out there in Vermont today. 

It's humid, and and the air is just not stirring. You'd think the air is just begging to unleash a late afternoon thunderstorm.  It is, but only depending on where you are.   

That still, windless air extends at least up to 24,000 feet overhead, which is quite unusual. There's really not much in the way of weak boundaries or wind shifts to trigger storms, since, um, there's no wind. 

There's only one way to force an updraft that could be a trigger for thunderstorms. That's the sun creating updrafts up the sides of mountains. Once it starts, the air in the updraft goes up and up and up, forming those billowing thunderhead clouds. Eventually a thunderstorm gets going.

That's a really typical scenario for a humid Vermont summer day. What isn't typical is the lack of wind through a thick layer of the atmosphere. Normally, wind would take those mountain thunderstorms out over the adjacent valleys, where they'd either continue on toward New Hampshire or dissipate.

With no wind to speak of that would move anything today's storms will hug the mountains. By that I mean mostly the Green Mountains, the Taconics of southwestern Vermont, along with the White Mountains of New Hampshire and New York's Adirondacks. 

The biggest risk of these stationary storms are along and south of Route 4 this afternoon. The remnants of a weak boundary that came through last evening is draped across that area. It's not creating any wind, but it is giving just a wee bit of extra lift to the atmosphere, which helps create storms. 

It already started late this morning and will continue on into the evening. Storms will continuously bubble up over the mountains, unleash torrential downpours. Then they'll dissipate, only to reform in basically the same spots again. 

That raises the risk of flash flooding. The air is humid enough to ensure any storms that do form unleash torrential downpours. Since the storms aren't moving much, the downpours last longer than usual in any given spot. 

The result is the continued risk of flash flooding, especially in the southern half of the region. 

Already, as of early afternoon, a couple flood advisories had been issued for southern Vermont, mostly around West Brattleboro and western Guilford, and around Jamaica and Wardsboro.  I'm sure new flood advisories and possible flash flood warnings will flash during the rest of the day in the mountains. 

Any flash flooding will be highly localized in just a few towns or even just neighborhoods caught under a persistent, stationary storm.  The vast majority of us will see no flooding. Many of us will see no rain at all today. Water might gush across a road in flash flood at one spot, while a mile or two up the road it's dusty and rain-free. 

Broad valleys like the Champlain Valley have the lowest chance of any rain today.  Local effects could push an isolated storm into the valley, but don't count on any rain at all today in places like Burlington, St. Albans, or west of Middlebury. If you're at a Lake Champlain beach, you'll keep getting plenthy of sun for the rest of the afternoon. 

It'll be interesting to see rainfall reports from the region tomorrow. You'll probably see many towns having received no rain at all today, a few will get modest amounts and a couple will just get slammed. 

If you live in or near the mountains today, keep away from small streams and creeks. Those can go nuts in no time at all.  Even if it's not raining where you are. It could be raining buckets at the stream's headwaters, and all that water could come rushing downhill. If you've set up camp right next to a stream, consider moving it uphill aways, so you don't have to scramble later.

It looks like the atmosphere, though remaining hot and humid, won't really be conducive to thunderstorms tomorrow and Tuesday, so there will probably be just isolated activity.  Thunderstorms could blossom again mid and late week over Vermont, but by then, it seems like there will be some wind to push them along.