Thursday, December 19, 2013

Messy, Icy, Icky Weekend In Vermont, But Just How Bad?

The only thing we can say for certain is the weekend's weather in Vermont is definitely going to be on the unpleasant side.
This map shows the probability of ice accumulations
of a quarter inch or greater between Saturday
and Sunday (click on the map to make it bigger)
A quarter inch or more of ice starts to bring down
branches and power lines.  

How exactly that plays out is up for grabs.

The overall scenario is that a boundary between cold Canadian air and unusually warm, springlike air to the south will set up somewhere over or near Vermont.

A series of storms will move northeastward along the front, the strongest of which will arrive Sunday.

There will be plenty of moisture to work with, so whatever comes down from the sky could come down pretty hard. Especially late Saturday night and Sunday.

The question is, what kind of precipitation will be get?

The National Weather Service in South Burlington lays out their thinking in this weekend's forecast, but of course they, and everybody else know the forecast could be a bust, given the tricky weather pattern.

The problem is, there will be a sharp temperature gradient on either side of the front, with temperatures in the 20s in southern Quebec to the 60s around New York City.

Where the front is at any given moment will determine which type of precipitation will fall at any given location in Vermont and surrounding states Friday through Sunday.

Overall, given the colder air to the north, it's more likely to be mostly rain in the south and mostly an icy mix in the north.  That part is obvious.

But as the front wavers back and forth, when will it be snowing and sleeting and icing and raining and when will the precipitation change from frozen to wet and back again?

Tricky, but overall, just plan on difficult driving conditions at any time Friday through Sunday, with the liklihood of trouble increasing the more north you go.  It seems that the best chances of ice and bad roads are early Friday, Friday evening, Saturday morning, Saturday night and again Sunday night.

But don't take that as gospel. Again, it depends on where that pesky weather front is.

The $64,000 question is whether enough ice will build up on trees and powerlines anywhere in the North Country. That's still possible.

The areas that have the best chance of seeing some damaging ice accumulations are in the St. Lawrence Valley in New York, the far northern Champlain Valley in New York and Vermont (most likely north of Plattsburgh, N.Y and Milton, Vermont) and in parts of the Northeast Kingdom of Vermont.

The intensity of the precipitation will vary from time to time and place to place, too. Much of Saturday will probably only feature light precipitation. Saturday night and Sunday morning look to have the heaviest.

In fact, most of Vermont will end up with more than an inch of rain (if you melt down the snow and ice that will be included in this) Some places could get more than two inches. That's pretty heavy for December.

Places that get mostly rain, especially in southern zones, there could be some flooding with this storm.

The storm which might also bring tornados to the Deep South and flooding rains to parts of the Ohio Valley, will move on Sunday night. It'll turn drier, and colder by Monday.

Your best bet if you're traveling this weekend, or wondering if the ice is going to snap your power lines, is to keep looking for forecast updates. The forecasts for up to 12 hours beyond the time your looking at them will probably be pretty accurate.

The forecasts for a day or two out might not be totally right, but will at least give you some hint of what to expect, even if it doesn't turn out exactly as planned.

If you're in Vermont looking for a white, snowy, winter wonderland this weekend free of trouble or ice or rain, though, you're kinda out of luck.

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