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    Snow for Some, and a Storm off the East Coast - The Devil Is in the Details

    11/08/2013, 7:31:54 AM

    Friday, 11:40 a.m.

    Some people have seen their first flakes of snow of the season in the past 24 hours around the Great Lakes and interior Northeast. There has been a couple of inches of snow a few of the more persistent bands off Lake Ontario, and this is in a modestly chilly air mass, not an exceptionally cold one!

    The makings are still there for a storm next week, and one that could bring accumulating snows to parts of Appalachia, the mid-Atlantic states and New England, not to mention more bands of lake-effect snow. Now the million dollar question on the minds of everyone is this: WILL the storm happen and bring accumulating snow to a wide swath of the East? The answer, unfortunately, remains elusive.

    Let me approach the problem this way today and break it down into two categories. One is 'what has remained the same?' and the other 'what has changed?' I think going through this exercise will prove instructive and may give us some insights as to how this can all unfold next week.

    What has remained the same?

    1) Two cold fronts will move from the Upper Midwest to the Northeast in the next four days. The first of these is tied to the area of low pressure that is moving through southern Saskatchewan at this hour. There are a couple of other low centers farther south, one over western North Dakota and the other in central South Dakota, with a cold front moving across Montana at this hour. This front will move off the New England and mid-Atlantic coasts later Sunday. Here's the 12z Nov. 8 NAM model surface forecast:

    There will be a slight surge of milder air into the Ohio Valley and mid-Atlantic states with and ahead of this front, and a slight bit of cooling behind it, more so back across the Midwest and Great Lakes into the northern Ohio Valley.

    If you look at that same map, you'll see the second front moving into Montana and North Dakota later Sunday, and it means business. By Monday evening, this front will have made considerable progress southeastward:

    By this time, arctic air will be drilling into Kansas and Missouri, and the colder air will also be building into the Great Lakes. This front should be reaching the East Coast Tuesday.

    2) There will be some snow behind the front. This has been my thought all along, that there will be some sort of streak of snow as moisture is pushed up and over the cold air drilling in at the low levels. Look at the 12z Nov. 8 GFS model 24-hour precipitation totals from Monday morning to Tuesday morning:

    It may not be a heavy snowfall, but it is quite conceivable that a few inches can accumulate, especially in some of the higher ground of the central Appalachians.

    3) There will be a storm off the East coast Wednesday into Thursday. That has not changed. It may be close to the coast, or it may not be, but there will be a storm! Now, if it forms farther offshore, then the idea of accumulating snows anywhere in the East can be pretty much tossed out the window! But should it hug the coast, as the European has been insisting, then there can be a snowstorm!

    What has changed?

    1) The very same European model has, as of its 0z run, shifted the storm farther east. It would pretty much leave the mountains high and dry AFTER the initial event on the back side of the cold front Monday night into. Here's a look at its total precipitation forecast (again, based on the 0z run) from Tuesday evening to Friday evening:

    Compare that to the current 12z GFS forecast:

    Just a little difference!

    For comparison's sake, the Canadian model is pretty much in the same camp as the GFS, as is the Navy NoGaps model.

    2) The attempt at downstream blocking appears to be minimized. Note carefully that any downturn in the NAO is well AFTER the potential storm!

    The lack of downstream blocking means the upper-level troughs should have a more progressive look to them, and, therefore, force storm development offshore.

    With all of that said, the door is still clearly open for a storm and the potential for a significant snowstorm. Remember from earlier posts this week, the pattern upstream in the Pacific is very amplified, and that means there is a lot of extreme undulations in the atmosphere. It would not at all be surprising to find the atmosphere downstream over the eastern U.S. in some way 'compensates,' or 'reacts,' to what is happening over the Pacific to the West Coast, by digging some sort of system so much that the low that does form off the East coast can't easily escape, thereby threatening the mid-Atlantic and New England with heavy precipitation - and yes, that means snow.

    From yesterday's standpoint, the snowstorm potential is diminished, but there will be snow for some, and there will be a storm off the East coast next week.

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


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