One Last Hot Day; Thunderstorm Chances Iffy Here In Vermont

Clear skies above the flowers on my St. Albans, Vermont

deck this morning. Another hot, oppressively humid day is 

on tap today, but it's the last in a series, for now.

There is a low chance of strong storms later.

 Thursday turned out to be mostly a bust for thunderstorms here in Vermont, despite almost all the ingredients coming together for at least a few severe storms statewide.  

A lack of damaging thunderstorms is of course a good thing, but still, forecasts were off. 

An area of clouds, mostly just left over debris from storms that had dissipated near the eastern Great Lakes earlier, came into Vermont around noon, was what prevented the storms.   Though the air was unstable, there wasn't much of a trigger to start the storms off. 

The trigger would have been strong sunshine, which would have created some updrafts to overcome what is known as a cap. A cap is a warm, stable layer of air a few thousand feet overhead that acts as a roadblock against the type of towering clouds that produce thunderstorms 

One way to break the cap is for sunshine to roil the atmosphere with updrafts below the cap.  These updrafts would poke at the cap a few thousand feet overhead, and finally break through.

Once the cap breaks, the clouds could tower to heights as high as 20,000, 30,000 or even more feet tall, which would be our severe thunderstorms. 

As those clouds arrived just when the sun would have been strongest, it prevented the updrafts that would have poked holes in that cap.  Which meant showers and thunderstorms were few and far between. None of few that formed north of Route 4 were severe. 

The clouds did hold temperatures in northern and central Vermont below 90 degrees, so the heat and humidity wasn't as terrible as forecast as well.

It was sunnier and hotter in the early afternoon in far southern Vermont, so an area of severe storms raced west to east along Route 9 between Bennington and Brattleboro

TODAY'S TRY AT STORMS

Today will be the last in a string of hot, humid days.  As of this early this morning, it was steamy, temperatures were rising rapidly and the sky was clear, with no signs of it clouding up anytime soon.

So a cap will break today and we'll get a lot of big storms, right?

Well, no. Not exactly.

Thunderstorm chances are there, but they look iffy, for slightly different reasons than yesterday. 

The hot high pressure that has been pumping the heat and humidity our way this week is reasserting itself. When high pressure builds like this, it tends to make air sink a bit, which inhibits thunderstorms. A few storms might overcome this sinking air this afternoon, but if they do get going, there won't be many and they probably won't last long.

Still anything that can get going in this soupy air today could be briefly strong, with a highly localized torrential downpour or two.

Otherwise, expect another oppressive day today with heat advisories once again in effect in Vermont's valleys.

By this evening, that beloved cold front in Canada will finally be making its approach toward Vermont.  That would increase the chances of showers and storms tonight.

But by then, we've lost the sun, so instability in the atmosphere will be waning. So yes, there will be storms around tonight, some with locally briefly torrential rains. But the storms will not be as widespread or intense as they would be had the cold front been approaching during the day.

That said, we're in a marginal risk zone for severe storms today and tonight. That means we can expect isolated instances of severe storms. 

This relative lack of rain is bad news for Vermont north of Route 2. Much of this area is still in drought, having missed out on most of July's heavy rain that hit much of the rest of New England.,

We're in for an extended dry spell, with the next chance of rain after this cold front coming along next Thursday.  And at this point, I'm not all that impressed with the chances for rain even then.

On the bright side,  you'll notice a dramatic change in the air happening during the day Saturday as the cold front sweeps on east of here.  It will be delightfully dry and pleasant Sunday and Monday.

More heat lurks, though, as a strong ridge of high pressure looks likely to re-establish itself over our neck of the woods next week.  It won't be as humid as this latest stretch was, but we can still expect highs well into the 80s all of next week after Monday.  Humidity levels, though falling short of this week's levels, will still creep up.