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    Strong Storm With Conflicting Model Forecasts

    2/11/2014, 7:25:01 AM

    Tuesday, 11:55 a.m.

    We're 24 hours closer to the unfolding of a major winter storm, and there are still some significant differences on the models as to how it will play out. On the one hand, the North American Models, namely the NAM and the GFS, are insistent on this storm crossing the Outer Banks of North Carolina during the middle of Wednesday night and never really slowing down as it moves steadily north-northeast to northeastward from there to a point near or just south-southeast of Nantucket early Thursday night. The precipitation is held within check, with the 1-inch precipitation line running from near Greenville-Spartanburg to Dulles to Philadelphia to Boston on the NAM model. Here's the 12z Feb. 11 run, and its 48-hour precipitation forecast from 12z tomorrow morning (7 a.m.) through 12z Friday morning (7 a.m.):

    The latest GFS is even lighter on the precipitation forecast on its western flank across Virginia. Here is its 48-hour precipitation forecast through Friday 12z:

    If the GFS ends up being more 'correct' with its forecast, then central and western Virginia into much of Maryland would probably get something on the order of 6-10 inches of snow, with locally a foot - a disruptive storm, no doubt, but not one that would be a record-setter. Closer to the coast, specifically from the Chesapeake Bay to Philadelphia to New York City to at least Boston and points east, snow amounts would definitely be cut into by a change to rain. Interior areas of southern and eastern New England would wind up with maybe 8 to 14 inches of snow with locally higher amounts, though in these areas it may qualify as a blizzard for a time as the storm winds up east of New England and generates strong winds that will cause some blowing and drifting snow.

    Meanwhile, the other camp is for a somewhat slower, more amplified storm that throws more moisture back through Virginia into West Virginia tomorrow afternoon and tomorrow. The European has been insistent on this idea, and the Canadian is aboard that train, as well as the UKMET and Japanese models. To give you an example, look at the 12z Feb. 11 RGEM model (regional Canadian) of 700mb heights and relative humidity, valid Thursday morning:

    The European 48-hour precipitation that would mirror the earlier NAM and GFS model forecasts looks wetter and farther west with its heavy precipitation shield. The scale colors are different, but you can clearly pick out the bullseye of precipitation in central, northern and western Virginia that the American models do not have:

    So, what do you want to believe? Well, let's go with the things we're most confident of:

    1) There will be a major snow and ice event across the northern Gulf Coast region into the Southeast. So far, it has all been north of Atlanta, limited to northern Alabama, and affecting portions of South Carolina. This is only with the first impulse coming across the Southeast. The real storm will develop south and east of New Orleans tonight, with a heavier band of precipitation growing north of the track of the low. Much of this will be rain for a while tonight, but as it expands across northern Mississippi into parts of Tennessee overnight and tomorrow morning, there will be some snow and sleet as well.

    The real problems, though, will come late tonight and tomorrow morning in northern Georgia and into central and upstate South Carolina, spreading into central and western North Carolina tomorrow morning, then across Virginia tomorrow afternoon. As the storm heads for the Southeast coast late tomorrow night, the snow will continue for a while over the western Carolinas before ending Thursday morning.

    2) There will be snow in most areas north and west of I-95 to the Appalachians. The core the snow will be in the northern and western suburbs of Washington, D.C., to Richmond to northwest of Charlotte, and it will also extend toward the Shenandoah Valley and up into the middle and lower Susquehanna Valley. Within the core of that area, there can be more than a foot of snow.

    3) East of the big cities, it will go to rain and cut down on accumulations. The closer to the coast, the warmer the air will get, and the more rain versus snow there will be, plain and simple, and that includes areas all the way to eastern Massachusetts.

    4) A deepening storm means strengthening winds and blizzard potential behind it. This is most likely across New England.

    5) Coastal flooding is likely along the northern mid-Atlantic and New England coasts. As the storm deepens, the winds will strengthen, and the onshore pounding will work at high tide when the tide cycle is already abnormally high. There will also be considerable beach erosion.

    6) The storm will take out the worst of the arctic air. It will not be warm behind the storm, but the deep arctic air in place now will exit. There will be a sloshing back of some of the colder air going into the weekend behind another upper-level trough that will generate some snow, but that weekend cold won't be as penetrating nor as widespread as the current frigid air mass is.

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


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