Friday, December 20, 2013

Icky, Icy Vermont: Ice, Rain To Continue Through Weekend

Well, it's certainly unpleasant in Vermont's Champlain Valley late this Friday afternoon. As expected, some cold air at low levels is bleeding into the valley, causing temperatures to drop below freezing.
This National Weather Service map
shows a high probability of at least a quarter inch
ice accumulation in northern Vermont.
(Click on the map to make it bigger,
easier to read)  

Meanwhile, it's still warm a few thousand feet overhead, so we've got a nasty mix of freezing rain and sleet out there.

It's not coming down particularly hard, but it's more than enough to ice up the roads. It's slow going out there. If you don't have to drive this evening, don't bother.

This is Round One of icy, rainy big storm I've been advertising.

I'm sticking by my prediction this could, maybe, be the Champlain Valley's worst ice storm since 1998. However, I do want to emphasize it won't be nearly as bad as the 1998 disaster. 

It's still kind of uncertain who will get the most freezing rain and how long it will last in one particular area. Southern Vermont is pretty safe from the ice. There might be brief mixes, but it will be mostly rain.

The northern Champlain Valley looks to have the best chance of a big ice accumulation in Vermont. It could well be enough to bring down trees and power lines by Sunday.

But it's still extremely unclear how much of the Champlain Valley might sneak above freezing for a time during the storm. It would be good if it does, because it would minimize the ice accumulation.

New York's St. Lawrence River valley seems to be even more at risk than areas near Lake Champlain for a big ice storm. Areas near Massena, New York might end up being the bullseye for worst of the ice.

It's really tricky to judge whether Vermont's Northeast Kingdom will get much ice. Cold air seeping south from Canada will easily drain into the Champlain Valley, undercutting the warm air aloft so that freezing rain can form. But in the Northeast Kingdom, it's unclear how much cold air will come down.

Mountainous areas of Vermont and New York will poke up into the warm air sitting atop the subfreezing air in the deeper valleys. So up in the mountains, I do expect quite a bit of rain but not all that much ice.

No matter what comes out of the sky --- rain, freezing rain and/or sleet,-- there's going to be a lot of it. This storm has incredible amounts of moisture with it. One computer model has the Burlington area getting the equivalent of three inches of rain in three days.

Normally, less than three inches of rain or melted snow falls in Burlington the entire month of December.

All this rain could lead to some flooding, especially across southern and central Vermont.  This will by no means be any kind of Irene-style flooding, but we could see some closed roads, flooded basements, that kind of thing.

It still looks like there's going to be an extreme temperature contrast across Vermont. Temperatures on Sunday could range from near 30 around Alburgh, Vermont to near 60 in Bennington, Vermont, a distance of only 145 miles as the crow flies.

The temperature difference between the two towns is usually not much more than 10 degrees.

This all clears out Sunday night, and we go back to pretty average weather during Christmas week.  Christmas Eve will be the coldest day of the week with highs only in the teens and lows near 0.

It's kind of iffy whether much of Vermont will get a white Christmas. In southern Vermont especially, most of the snow that's now on the ground will melt by Sunday, and prospects of a replacement snowfall by Christmas are kind of dicey.

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