Saturday, January 17, 2015

New England Storm Forecast Update: Damn Tricky Business Here

The National Weather Service in South Burlington,
Vermont has taken an initial stab at forecasting
how much snow is coming, but this map is
BIG Time subject to change. (Click on the image to
make it bigger and easier to read.)  
Up here in Vermont, the National Weather Service in South Burlington has this evening opted to hold off on upgrading a winter storm watch for Sunday night and Monday into a warning.

They have good reason to be hesitant. This storm has a super high forecast bust potential. Vermonters hoping for a good dump of snow better not start celebrating yet.

There's still a very good chance of four to 10 inches of snow in Vermont, but there are a lot of complicating factors.

The National Weather Service forecast discussion is illuminating as to why the entire staff in South Burlington will be bald by Monday because they're pulling their hair out over this one.

Here are the problems:

1. Temperatures will be margional for snow, especially during the first part of the storm. It looks like many areas will start off as rain. But will the precipitation change over to snow as soon as the heavier precipitation comes in?

If not, who gets rain, and which areas stay cold enough for snow?  The higher elevations, of course, would be more apt to get snow, but what about the Champlain Valley? The valleys around Rutland?
How far do you have to go east of the Green Mountains before you encounter mostly rain?

A degree or two off in the forecast for any layer of the atmosphere, not just the surface, and current forecasts would be wrong.

2. Where will the heaviest precipitation be? There's a sharp cutoff expected between heavy snow or rain to the east, and very light precipitation to the west. Right now, it looks like the heaviest precipitation will be from the Champlain Valley east.

Even if forecasters are off by as little as 20 miles as to how far west the heavy precipitation will get, some areas will miss out on the heavy snow, or, in the case of eastern New York, unexpectedly get dumped on.

By the way, a 20 mile error in this regard is practically inevitable at this point.

3. These kinds of storms often form what is called a deformation zone, which is an area of heavier precipitation on the western edge of a storm that stays put for a few hours. Will a deformation zone set up? If so where?

4. Will mountains block the moisture feed in some areas? That's especially a risk west of the Green Mountains and even more so in Vermonts Northeast Kingdom, where New Hampshire's White Mountains could block the moisture.

You can see why Vermont is still under an uncertain winter storm watch. Who the hell knows what this storm is going to do?

The going forecast now, definitely subject to change, calls for about a foot of snow in the high-ish elevations in far north central Vermont, especially around Jay Peak.

Northwestern Vermont, especially areas at least five miles east of Lake Champlain, are pegged to get 6 to 10 inches of snow.

The Champlain Valley south of Franklin County, and central Vermont are up for four to eight inches.

Southwestern Vermont would get 1 to 4 inches of snow, and only an inch or two will come down in the Connecticut River Valley south of St. Johnsbury

As I noted, this snow forecast is BIG TIME subject to change.

By the way, things are just as uncertain in northern New Hampshire. They might get a big snowstorm, they migh not.

Down in Massachusetts, the NFL Patriots vs. Indiana Colts game, scheduled to start at 6:40 p.m. Sunday, promises to be a really unpleasant slog in the weather department.

Rain could come down pretty hard, and temperatures will only be in the low 40s. There's even a chance of thunder. However, there's still a chance the heaviest weather could wait until after the Patriots game. We'll wait and see on that one.

After the storm, the weather looks very easy to forecast, at least by comparison. It'll be a little colder than normal through most of next week, with just chances of light snow here an there across northern New England

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