Thursday Morning Update: Shaping Up To Be Another Dangerous Vermont Storm Day

The National Weather Service in South Burlington 
released this helpful schematic illustrating where
they think today's line of storms will hit when,
and what it might look like. Actual results will
probably vary, but this gives a really good
idea of the expected situation. 

I wish I  had better news, but Vermont appears to be in for more storm damage today. 

There's all kinds of hazards with today's weather, renewed flooding of course being the primary one. But there's a good chance some towns will suffer damage from high winds.  It's possible one or two places could have large hail.   

There's even a very small, but not zero chance of a brief tornado west of the Green Mountains. 

Once again, be weather aware and ready to see, shelter or evacuate if things turn ugly.  If they do turn ugly, it'll happen fast, so be on your toes. 

I will emphasize that the trouble today and tonight, while significant, will NOT be as widespread as earlier this week. The new damage will be rather hit and miss.  Although flash flooding could occur later today and tonight anywhere in Vermont, the southern half of the state is most at peril.

THE DETAILS

Patchy rain was moving through Vermont early this morning. It was pretty light, and won't cause any immediate issues.

That rain is a part of a warm front, which will lift into Canada pretty quickly. This will put us back into the soupy, humid air. And the sun will come out. 

That sun, interacting with the humid air, will destabilize the atmosphere. Meanwhile yet another robust disturbance is approaching from the west.  

There will be some rotation in the lower parts of the atmosphere, so that could set off a rogue supercell thunderstorm or two. 

Mostly, though, a line of thunderstorms will form.  I suppose there could be a few spin ups in this line which is why there's that very small, but non-zero tornado threat. However, almost all of the wind threat is from straight line gusts with the more severe thunderstorms. 

As an aside, there's a greater risk of tornadoes, a couple possibly kind of strong, up in Quebec between Ottawa and Montreal.

The ground is so wet that tree root structures can't hold as easily. So there's a risk that more trees than usual will topple in any of today's thunderstorm winds. That means new power outages as well as some of the falling trees get tangled in wires.

One thing to keep an eye out for is something called a bow echo.  That's when a line of storms arranges itself to look like a backwards "C".  At the apex of the "C" winds can get awfully intense and destructive. It's a possibility to look out for. 

Flooding

Flooding is a greater threat, as mentioned. Any storm will be able to drop an inch of rain or more in a short period of time.  Under normal circumstances, this is enough to cause perhaps some minor flash flooding but not enough to create chaos.

However, everything is so unstable and so wet, so that will magnify the problems posed by any heavy storms.  

Once again, Vermont is one of the main
trouble spots for possible flooding today. 

NOAA's Weather Prediction Center has all of Vermont in at least a slight risk of flash flooding today and tonight.  They've upped the chances to "moderate" in the state's southern four counties. That's just a a step below the high risk we were in Monday.  Moderate also means that some flash flooding is inevitable, and there could be pockets of substantial flash floods.

Part of the reason for the added concern in southern Vermont is that line of storms that's expected might slow down and linger in that part of the state. That would set up the risk of the dreaded training storms, you, know, the boxcars going over the same spot repeatedly that I keep bringing up. 

Most of the flash flooding will come from small creeks, brooks and streams. It doesn't look like this new episode will put main rivers like the Otter Creek, Winooski and Lamoille rivers back into flood. The rivers will probably start to rise again after today's rain, but stay within their banks and not cause new damage.

That said, we'll still need to watch the capacity of Wrightsville Dam above Montpelier and southern Vermont dams as well. 

Timing

Some isolated rogue thunderstorms could fire up in advance of the main show, but those will probably be few and far between. 

The National Weather Service in South Burlington projects the line of storms to begin firing up over central New York by mid-afternoon. This growing line storms would then start to move into western Vermont around 4 or 5p.m., give or take. 

The line will then plow west to east through Vermont in the late afternoon and evening.  Again, I am worried about this line lf storms slowing down, especially in eastern and southern Vermont. 

Still, this batch of storms should move out of Vermont by midnight at the latest.Of course, run-off from the storms would continue after that. 

NOT OUT OF THE WOODS

The same stuck weather pattern will keep Vermont and surrounding areas in flood peril beyond today and tonight.

More thunderstorms will fire up tomorrow, and possibly Saturday in Vermont.  The biggest risk again is southern Vermont. However, Friday and Saturday will represent a bit of a lull. Any new flash flooding will probably be fairly isolated and localized.

Another surge of deep moisture Sunday could create new issues. Yet another surge next Tuesday could get us in trouble again.  Details on those events are TBA.  It's too soon to get into specifics. 

Long term forecasts into the end of July -admittedly not very reliable forecasts - don't really seem to get us out of the wet pattern. 

This could stick around for awhile.