Soupy Air, Likely Heat Advisories And Local Flood Risks Through Tuesday In Vermont

Here's an interesting visible satellite photo taken shortly
after 5:30 p.m Thursday. The white blob in southwestern
Vermont is a severe thunderstorm. Severe storm clouds
tower up to 40,000 feet in the air. So you can see 
the dark areas in southeastern Vermont and northwestern
Massachusetts. Those areas were in the shadow of these
very tall storms. 

UPDATE 3:30 p.m. Friday.

I anticipated this, and now it's official. Heat Advisory in effect for parts of Vermont over the weekend. 

It's a long lasting one, starting at 1 p.m. Saturday and going to 8 p.m. Sunday.

I think the National Weather Service is letting it go that long since Saturday night won't offer all that much relief. Many of us will stay in the humid low 70s at night. 

As far as torrential rain and flash flood chances, they're nil for the rest of the day and night in northern Vermont as that boundary of sorts has made it in, shutting off storms. 

There's a few isolated storms forming in the southern half of Vermont, and it's still possible one or two could be heavy rainers.

Only isolated storms are in the forecast Saturday, but one or two spots could get deluged. Again, it will be isolated.

There's a slightly better chance of storms Sunday with the best chance of heavy rain still looking like Monday and Monday night

PREVIOUS DISCUSSION

As expected, the air turned soupy as hell in Vermont yesterday, and we're stuck with this sticky air into Monday.

The incredibly high humidity for this time of year sets the stage for torrential downpours here and there. until more refreshing air finds its way to northern New England. 

It's classic flash flood weather, but I don't want to sound too alarming.  It just means that in some slow moving showers and storms in this weather regime, you can really pile up a lot of rain fast.  Few of us will actually see real trouble from this.  But there's a chance of local flash flooding into early next week. 

You can tell the risk is still quite low because I don't see any flash flood watches or alerts for anywhere around Vermont. But the risk is not zero. 

Just by walking outside, you can tell if there's the right trigger, the rain will come down in buckets. 

 When I walked out into my yard last evening, it really felt like air you could wear. You could actually kind of see the air.

It's only a slight exaggeration to say that I wasn't sure whether I was walking across my yard or swimming across it.  

Yesterday, clouds helped prevent both torrential thunderstorms and dangerous heat from building across the northern half of Vermont. But it southern Vermont, it got torrid, and the reward for that heat was some hefty thunderstorms, some of which carried warnings of damaging winds and such. 

The storm was particularly ferocious in the southwestern of Vermont, with lots of trees and wires down, some blocking roads, in Pawlet, Arlington and Bennington.  We have reports of similar damage in southeastern Vermont, around Newfane, Jamaica and Rockingham. 

These storms also dumped a good inch or more of rain easily in less than an hour. If those areas get additional torrential rains today, there could be some water issues there. 

More storms developed in the humid air this morning.  Residents around Hinesburg and Huntington awoke early this morning to quite a lightning barrage.  This storm dumped up to 1.5 inches of rain in a short period of time in parts of Chittenden County. The National Weather Service in South Burlington said the downpours fell just short of them needing to issue any flood advisories. However, they are watching this area in case they receive more buckets of rain later today.    

The root of all this potential trouble with water is a sluggish atmosphere and weather fronts lining up the "wrong" way. 

Most of the time, cold fronts that pass through Vermont are oriented in a generally north to south arrangement, while the air flow pushing the front is more or less west to east.

Which means that if that cold front can manage to create heavy rains, it won't last long in any one spot. The cold front will zip on through, and drier, rain-free air is hot on its tail. 

With the current weather set up, cold fronts or just weak nothing burger boundaries are kind of oriented west to east. So is the general air flow. So these fronts press southward only very slowly. Meanwhile, showers and storms move along the front or just ahead of it, west to east. That's the training I've been talking about. Storms repeatedly go over the same spot, and you get tons of rain.

Especially if the air just ahead of these fronts or boundaries is super humid. Which is what we're dealing with now. 

Then there's this added bonus. Around this time of year, the jet stream often retreats well north into Canada. 'Which means there's nothing to hurry anything along. So if thunderstorms form in the humid air, they don't move very fast. They dump a lot of rain in the same spot

On top of all that, there's something called backbuilding. Here's how that works: Say you have a mountain that creates a strong enough updraft to set off a thunderstorm.  That storm starts to move on to the east, but the updraft continues, so the storm keeps redeveloping over that same mountain, over and over until you get inches of rain.

There's no telling whether any of these scenarios will develop over the next few days anywhere in Vermont, but there's that low, but not zero risk that it could.

 Some of the heaviest ones today, especially if a particular spot gets several downpours in a row, could produce some ponding on the roads. There's a weak excuse for a weather front around Vermont now, oriented west to east, with showers moving along it.   As I write this early today, more downpours were lined up in New York, ready to come across Lake Champlain and hit north central Vermont again. Just like the earlier downpour. 

The weather front wannabe is is slowly sagging southward across Vermont while dissipating, so downpours will probably get more scattered, especially north.  So, I have a feeling this morning's downpours will begin to wane a bit, especially north.

Also, you might get some gullywashers, damage to the side of gravel roads or driveways, that sort of thing. Nothing widespread, though.  

In the hot, humid air that will be over us all weekend, there won't be much there to trigger thunderstorms. So they will probably be few and far between both days. 

However, isolated, slow moving storms could form in the updrafts in the mountains, which could unleash more torrents of rain in just one or two spots. In any event, take it easy this weekend. The combination of heat and humidity will make vigorous outdoor activity rather dangerous. 

Another front, a "real" cold front, looks like it will slowly shift north to south across Vermont early in the week.  Again, the flow will be parallel to the front, so that means we could get those "training" storms again, one after another over the same spots. 

We'll need to wait until we get closer to the beginning of the week to see how that all shakes out.