Wednesday, January 8, 2020

Still Watching Dangerous Weekend Storm In Eastern U.S.

Forecast national map for Saturday. Note the very
strong high pressure off the East Coast pumping in
lots of very warm, wet air from the Gulf of Mexico. Storm shown
centered over Arksans will produce severe storms
and tornadoes south and east of it and ice to its northwest.
The storm moves into our area Saturday and especially
Sunday, with a risk of heavy ice or rain, and
possibly snow. 
Ingredients continue to come together for a dangerous storm in much of the eastern United States Friday through Sunday.

While forecasts will undoubtedly change somewhat as more updated data comes in, here's a quick broad brush of what the nation should expect, followed by effects here in Vermont.

Friday:  A line of severe thunderstorms and possible tornadoes develops in eastern Oklahoma and Texas and moves into Arkansas and Louisiana. Strong, damaging thunderstorms and a few tornadoes along this line.

Ahead of the squall line, a few supercells with possible tornadoes, might well develop, with the risk of a very big, strong tornado or two.

Heavy rain will develop in the Tennessee and Ohio valleys later in the day. There will be a freezing rain risk from about Nebraska to southern Wisconsin.

Saturday: The threat of severe storms and tornadoes will shift to the central Gulf Coast and lower Tennessee valley. Overall this two-day severe outbreak might resemble one of the stronger outbreaks more common in the spring and early summer.

Meanwhile, heavy rain and the threat of flooding will develop from the Gulf Coast through the Tennessee and Ohio Valleys and extend as far north as Michigan. There's a risk of a good amount of freezing rain in a broad band from Kansas, through Missouri, into northern Ilinois, Michigan and into Ontario.

Near record warmth will affect the East Coast.

Sunday: The heavy rain shifts to eastward a bit and then diminishes, except north. . Heavy precipitation moves into northern New York and northern New England, and southern Ontario and Quebec. These areas will turn colder and there is a risk of heavy icing in some of these areas. Another day of record warmth is likely along the immediate East Coast.

Lets look at the next few days in Vermont:

Today: Snow showers with a cold front. Sharply falling temperatures this afternoon with the snow showers could cause a flash freeze on roads.

Thursday: Quiet and cold.  Lows a few degrees either side of zero, highs in the teens. At night, south winds start blowing, becoming strong in the Champlain Valley.

Friday: Windy and warm, with patchy light rain. A little ice possible east of the Greens in the morning.

Saturday: Now we're getting into the meat of the storm.  It'll be warm, unless the cold front comes in sooner than forecast. A few record highs possible. Rain is likely, especially north.  Turning sharply colder, especially north and west Saturday night with possible mixed precipitation.

Sunday: A wild card, with a complex thermal profile and questions about the position of cold air. There's a risk of significant, damaging icing, especially north. If it's a little warmer than expected, rain could be heavy enough to produce flooding. If it's a little colder than now expected, more snow would work into northern areas.

Overall, it looks like one to two inches of rain and/or melted snow and ice will come down northern Vermont Sunday. That's a lot for January. Somewhat lesser amounts of precipitation will probably hit southern Vermont.

The bottom line is, we don't know exactly what will be falling from the sky Sunday, but I'd consider postponing travel. And pay attention to those iee forecasts. If we got a lot of ice, we could lose quite a few trees and power lines.  If the forecasts for ice become more certain, stock up on supplies during the warmer weather Saturday morning and afternoon.

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