Joe Lundberg

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Cold and Snow for the Traditional Coldest Week of the Year

January 21, 2013; 9:12 AM ET

Monday, 11:15 A.M.

If you examine the average temperatures across the country, you'll find that the lowest average temperatures generally occur this week. After that, the averages slowly but surely start to rise. So even though we've gained more than 30 minutes of day light since the winter solstice, the radiation balance is such that the lowest annual temperatures occur about a month after the solstice. And look what's coming this week.

Perhaps you may have heard of this old 17th century English proverb: "As the day lengthens, so the cold strengthens." Last winter, you really couldn't say that, as it was mild most of the winter season. This year, not so much. After a mild weekend in the East, the arctic air is just now starting to move in. It's already in place across the Dakotas and Midwest, where most places were well below zero this morning:

This air mass is by far and away the coldest so far this season, or will be as it reaches the East tomorrow. Yes, there was a cold front that rolled through the Northeast and mid-Atlantic states yesterday, wiping out the springlike warmth as the day wore on. But the air mass in the mid-Atlantic states is not that cold. Temperatures for highs today across Maryland, Virginia and Delaware will be pretty close to average for Jan. 21. But the real cold is coming.

An upper-level disturbance is cross the Lakes and Ohio Valley right now, spreading clouds into the mid-Atlantic and New England:

There will some light snows with this across portions of the Ohio Valley into New York and Pennsylvania, but snow amounts will generally be an inch or less in most places away from the influence of any kind of upslope flow or lake effect. There will be more, of course, on Long Island and into southern and eastern New England. This has been expected for days, and is of no surprise. Some places on the eastern New England coast will get more than 6 inches of snow, and it will be accompanied by some pretty gusty winds to blow that snow around tomorrow.

Once this feature passes, then the really cold air moves in. If you examine a temperature map of the Ohio Valley, you'll find that current temperatures run form the 20s in most of Ohio to the upper teens in the northwest corner of the state, to the single digits north and west of Chicago. That's the impact of this disturbance. Temperatures tomorrow will be in the 20s around Washington, D.C., rather than near or even above 40 today.

The bitter cold lasts about three days in any given location. It will be slower to retreat from New York and New England, as the next storm coming along in the pattern will be unable to eradicate it completely Friday and Friday night into Saturday. Modify it, yes. Eliminate it, no.

That late-week storm is still on track to come farther north than you might think. Part of the reason for that is the storm that'll be developing off the mid-Atlantic and New England coasts tonight. By Thursday morning, that same storm will be near the southern tip of Greenland:

Before we get to Thursday, there will be another little disturbance zipping across the Northeast later Wednesday and Wednesday night that will be starved for moisture, so about all it will manage to accomplish is to generate clouds and scattered snow showers, and then reinforce the cold going into Thursday. It will set the stage for the resistance that it will offer up going into Friday as that storm you see in Kansas develops and comes eastward.

The models over the weekend have begin to converge on a storm track that will take the primary low into the Ohio Valley, where there will be less resistance to warming. That means areas to at least the I-70 corridor, and probably somewhat farther north, are likely to see a mixed bag of precipitation. That includes snow and ice, and may include plain rain, especially in southern Ohio and Kentucky.

What's less certain is how far north that warming gets east of the Appalachians. Eventually the presence of that big storm southwest of Greenland will force the storm to go around it. But does that allow the surface low to get to the southern New England coast, as the Canadian model suggests?

The JMA remains farther north, while the European has trended south since Friday. The GFS has maintained some degree of consistency, amazingly enough, though its 6z run not only trended south, but vastly weaker, largely sparing the Northeast of any meaningful snow with that event. I'm still of the opinion that warm air will make enough inroads to the north aloft to at least threaten the southern New England coast with a changeover to ice or perhaps even plain rain. It's much more of a concern around Philadelphia, and it's all but certain, in my opinion, around Washington, D.C. I would like to see a stronger block around to force this storm farther south before I'd take those options off the table, but there's not enough evidence to fully support that idea.

Even with that as a concern, there should be enough cold air in place ahead of the storm and ahead of the warming for snow for at least part of the storm in New York and Boston, and probably even Philadelphia, if not Washington, D.C., but the duration of the snow and the timing of any changeover will determine who ends up with more snow in the end.

Regardless of how that is fleshed out in the end, it will turn very cold again right behind the storm. However, this time the cold won't be anywhere near as impressive in the Midwest and Great Lakes into the Ohio Valley, and may end up a little weaker in New England, too. Furthermore, the length of the cold air influx behind the storm will be shorter by a day, allowing much milder air to sweep across the country from the Rockies onto the Plains states this weekend, and then all the way to the East Coast by early next week.

The views expressed are those of the author and not necessarily those of AccuWeather, Inc. or AccuWeather.com

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About This Blog

Joe Lundberg
Joe Lundberg, a veteran AccuWeather.com forecaster and meteorologist, covers both short and long-term U.S. weather on this blog.