Thursday, December 21, 2017

Complicated, Messy Christmas Weekend Weather On Our Doorstep

Here's what the National Weather Service in South
Burlington, Vermont is thinking for snow accumulation
Friday. The most will fall in southern Vermont. Click on
the image to make it bigger and easier to see. 
If you want a day to travel or finish your errands here in Vermont before Christmas today's your day.

Sure, it's kinda chilly out, but there will be a fair amount of sun. Roads are pretty clear. The only
chance of precipitation is maybe, just maybe a flurry over the mountains or near Lake Champlain.

Then it's a mess for days. At least I think so. Christmas Day remains a HUGE iffy wild card. More on that in a minute.

Let's get through the first wave of storminess first. This first wave, due Friday and early Friday night here in the North Country will almost exclusively come in the form of snow. It's a repeat of this past Monday, except more snow will come down in most places than on Monday.

Expect a general three to seven inches of new snow. The most will come down in south central Vermont, especially in the mountains roughly between Rutland and White River Junction. The least amount will hit near the border with Canada.

It's all enough to prompt a winter weather advisory for Friday. The morning commute might be tricky in southern Vermont. It'll be a slow mess region wide Friday evening, so get ready for that.

That's round one, which will peter off to scattered freezing drizzle late Friday night.

Round two comes Saturday, and that one will be a real mess. Before I get into it, do understand that temperatures will be pretty marginal on Saturday - right near the freezing mark - so things will probably not work out exactly as forecast then. But it's enough in the general sense to be prepared for some rough travel, and some extremely icy conditions in some areas.

As it stands now, mixed precipitation will probably change to a cold rain over western Vermont and  most of eastern New York during the day Saturday. Messy, and an icy morning, but perhaps not the end of the world.

I'm definitely worried about the St. Lawrence Valley of New York, the eastern half of Vermont, especially the Northeast Kingdom and a large chunk of central New Hampshire. In these areas, precipitation has a really good chance of staying in the form of freezing rain and sleet.
Here's one computer model's take on the freezing rain
potential Saturdau. The deepest pinks are where
the thickest accumulation of ice is expected -
a quarter inch or more. 

That's because cold high pressure is going to keep feeding low level cold air down from the north into this region. Meanwhile, a surge of very warm air will ride up and over this cold low level air. A perfect recipe for freezing rain, even an ice storm.

It's possible that ice could accumulate to a thickness of a quarter to a half inch in a few places in the colder areas I just outlined. Not only is that enough to make the roads dangerous, it's also beginning to get into the territory where the weight of ice could bring down trees and power lines.

On the bright side, one storm on Saturday will come up into New York State and weaken, while a second storm forms along the New England Coast. Neither will really fully get their acts together, so precipitation won't be quite as heavy as it otherwise could have been.

Still, I'm certain new winter weather advisories or other winter weather alerts will go up for the region on Saturday. They haven't yet only because the National Weather Service doesn't want to confuse people because they already have advisories up for Friday's snow.

Back here in Vermont, the cold rain will likely change back to snow Saturday night, then taper off, but not before accumulating at least some. Plus all the water will freeze back up, and the ice from the storm will stay put.

Definitely dangerous underfoot for walking beginning Saturday and lasting into the foreseeable future.

On Sunday, it looks like we'll be between systems, so that might be the time to sneak off to your destination. It won't be perfect. I imagine there might be sone snow showers around, plus we're all have that remaining ice on the ground to deal with.

Then we get to Christmas Day, and there's still a huge number of question marks surrounding the potential for maybe, just maybe a substantial snowstorm. The American computer models don't develop much of anything, and push whatever forms well south and east on Vermont. Translation: The American models aren't forecasting any major snows for Vermont on Christmas Day.

The European Model, however, brings a nor'easter along the New England coast and dumps a lot of Christmas Day snow on Vermont. However, the European model did trend a bit east this morning, which would cut back on the snow here in the Green Mountain State. We'll see if that eastward bump is a trend, or just a blip.

The bottom line is it's still anyone's guess as to what will happen with the weather on Christmas Day.

Elsewhere in the nation, bitter cold air is surging into the northern Plains and will gradually spread south and east. Parts of North Dakota and Minnesota won't get above zero from Sunday evening to at least Wednesday.

That cold air will arrive here in Vermont starting next Tuesday, which means a round of subzero nights for us next week.

In southern California, unbelievably, the fire risk continues amid strangely dry conditions. The highest threats are today and Sunday, when winds are forecast to be strongest.

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