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    The Cold and the Friday Storm

    1/22/2013, 6:57:50 AM

    Tuesday, 11:35 a.m.

    From the northern Plains and Midwest to the mid-Atlantic and parts of the South, the arctic air is in place. The disturbance that brought some light snow across the northern mid-Atlantic into New England has helped drag the frigid air to the south and east. Now that it is in place, it will stay for a spell. There aren't many record lows, but we're not far from some, that's for sure. It's as cold of an air mass as we have seen in the past two or three winters, and there may be one coming for the beginning of February that's every bit as cold, maybe a touch colder. And that one has a better chance of drilling farther south, reaching into Florida. We'll deal with that more after we get to this weekend.

    In the meantime, we're back to a pretty dry weather pattern for a brief period of time. Even that system yesterday was somewhat of an underachiever. There was less snow from New York to Portland, Maine, than many had either projected, or hoped for, or both! Most of the accumulations were under 3 inches, save for parts of Long Island and Cape Cod. Even there, most places didn't get more than about 5 or 6 inches.

    Another relatively weak and moisture-starved, upper-level disturbance will streak southeastward from the Upper Midwest late tonight and tomorrow morning, then dart across the Great Lakes and Ohio Valley and through the mid-Atlantic states tomorrow into tomorrow night before streaking into the Atlantic. As far as snow is concerned associated with this feature, there won't be much. Most of it will be in and around the Great Lakes to the upslope areas of Pennsylvania and West Virginia. Truth be told, it will be hard to distinguish between the snow associated with the actual disturbance and the snow that would be falling because of the cold flow over the open lakes and into the higher ground of the Appalachians! Regardless, in most cases, it's not going to be a lot, and the amount of water within the snow will be very low.

    Then there will be a more important feature coming along in the flow that will cause more generous precipitation to break out over time Thursday night into Friday as it moves pretty quickly eastward from the Mississippi Valley. It's actually part of a system bringing some clouds into the Pacific Northwest right now. Eventually late tonight and tomorrow that will mean some rain from northern California into western Washington, with some snow in the northern Sierra and the Cascades.

    There will probably be two pieces to this upcoming storm. Take a look at the 12z NAM forecast for Friday morning, as an example:

    Of the two pieces, the northern one won't have much moisture to work with, but it will help pull more cold air back into the pattern behind it. Better yet, it will ultimately renew the cold, as temperatures on the back side of it won't be as low as they are right now, yet will remain below normal from the Midwest on Friday, then into the Great Lakes and Ohio Valley Saturday, and the East later Saturday into Sunday.

    The southern half of this equation will have the water with it. It will try to push into the pre-existing arctic air but will have limited success in doing so. In the end, the storm will 'feel' a storm well to its northeast and try to avoid it. That storm is the one speeding away from New England, the same one I've been talking about since Saturday that will blossom into a much deeper system and do an anticyclonic loop back across the southern tip of Greenland Thursday morning, then stall Thursday night and Friday between there and Labrador. The storm will effectively wipe out any blocking over the North Atlantic, but its presence will be enough for the system coming at the Ohio Valley and East Coast to find a way to go around it.

    The trick in figuring out the details of the forecast is to know how far north that storm will come before reorganizing off the mid-Atlantic coast. Since late last week I've been trying to give you a run down of what the various modeling is doing with the storm. Clearly the trend is farther south while the idea of a primary storm cutting into the Ohio Valley before a secondary low forms off the mid-Atlantic coast is losing support on the models.

    The GFS as of its 6z run has the weakest storm. It keeps the two entities separate and speeds the southern system out to sea Friday night, leaving much of New York and New England with little snow, and not an awful lot in the mid-Atlantic, truth be told. The 12z NAM has a somewhat similar idea, with a separation between the northern and southern stream features. It does, however, spit out more precipitation later Thursday night into Friday as the primary low gets to Kentucky, then reappears off the Delmarva Peninsula Friday evening. It would also mean the possibility of a changeover event limited to areas along and south of the Ohio River and all snow from central Virginia on north.

    The European model remains the most developed of all the models, as it feeds the energy from the northern stream into the southern storm, blowing it up along and off the mid-Atlantic coast. Of all the models, if you are a snow lover, this is the one you want to see verify! It would dump a foot of snow on New York, and more across much of southeastern New England where there's no mixing. That wouldn't be a large area if that exact model track were to work out precisely.

    The Canadian is actually pretty similar, when you get right down to it. And the JMA remains the farthest north, developing the storm much more quickly in the Ohio Valley and is the farthest north with the warm air.

    As you can see, the options remain varied. In a place like Washington, D.C., you could see anything from a few inches of snow to a couple of inches, followed by sleet and freezing rain or snow to ice to rain. In Boston, it might be little snow to a ton of snow, or even some snow mixing with sleet and freezing rain or even plain rain if the developing storm intensifies quickly enough to wrap enough warmth inland from off the Atlantic.

    More often than not, though, the middle ground ends up being the way to go. Model ensemble guidance leans toward a pretty deep trough moving off the East coast Saturday morning, which tells me the internal consensus of any given model is strongly in favor of phasing. That means with all of the arctic air around north of the storm, there could be some potentially deep snow, especially New England. This might be the way to get something akin to a classic nor'easter, though its origins won't be the southern Plains of the Gulf of Mexico.

    By the way, I just looked at the 12z GFS just in. It continues its own trend of keeping the systems separate and squashing the storm. My gut tells me that's not going to be right in the end.

    Once the storm departs, it'll be cold but mainly dry this weekend from the Great Lakes and Ohio Valley to the East Coast. Late in the weekend, though, a system coming out of the southern Plains will push the arctic air aside a little more forcefully going into next week. It'll lead to a three-day reprieve from the bitter cold, but that may be it. Looking even farther ahead, they might want to find some way of keeping the den of Phil artificially warm. Another blast of bitter arctic air may be waiting in the wings by Groundhog Day. Just sayin'...

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

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