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    Nor'easter Winding Down, With Action Shifting West

    11/08/2012, 8:15:43 AM

    Thursday, 11:10 a.m.

    The nor'easter took a track off the mid-Atlantic coast and just southeast of Nantucket this morning. At last check, winds were still gusting over 50 miles an hour across the Outer Cape and to 40 miles an hour across much of southern and eastern New England. The track was one that meant two specific things with regard to what happened with the storm. For starters, it allowed the cold air to get right to the coast, which translated to all of the snow that was seen at the Jersey Shore, Long Island, New York City, and throughout most of southern New England, especially Connecticut. I completely underestimated the snow potential of this storm, a wild 'swing and a miss' on my part. The upward motion associated with this intense storm was more than enough to overcome what little warmth there was in the boundary layer from off the Atlantic, in large part because the dew points started out in the 20s ahead of the storm. Also, with the storm track that far away from the coast, the wind had more of a northerly component to it, more off land that water, enough to make that critical difference between a miserable, wind-whipped, cold rain and a heavy, wet snow.

    The other aspect of the storm that a farther east storm track directly contributed to was the lack of precipitation across most of Maryland and eastern Pennsylvania. In fact, in those areas, what precipitation occurred there was light enough that it did come down more as rain than snow, even though the air aloft was cold enough to support snow. Interesting stuff when you have the chance to sit back and analyze it in hindsight. Unfortunately, that doesn't help much going into it.

    With the nor'easter winding down this afternoon and tonight and speeding up on its exit from the New England coastal waters, our attention is shifting to the West. The week opened with record warmth throughout the West, and there were record highs throughout Arizona yesterday. Look at the highs from Wednesday:

    That 73 in Billings, Mont.? Good luck seeing that the rest of the year! It mat not get much above 40 this afternoon, and there will be snow at times tonight into early Saturday there, and when you add it all up, there could be more than a foot of the white stuff in parts of Montana. An early projection from here at AccuWeather.com:

    And not just snow, but wind also. Enough that when combined with what will end up as powdery snow, will lead to a lot of blowing and drifting snow and blizzard, or near-blizzard, conditions for a time going into the weekend.

    As this whole trough rolls down the West Coast this afternoon and tonight into tomorrow and progresses inland tomorrow night and Saturday, it may cause snow in the mountains outside of Los Angeles. Yes, it's that strong of an upper-level trough, and the air associated with it is that cold. It may not snow a lot, but considering how warm it was to begin the week, it will be complete culture shock.

    If you step back and look at the pattern as a whole for the next week, a couple of things quickly jump off the page. For one, the blocking that has been so prevalent and so strong the past several weeks flat out disappears. Look at the NAO chart:

    That block has directly contributed to both Sandy becoming the monster it was, and the nor'easter slowing down and deepening off the East Coast before being allowed to escape.

    With the blocking gone, the other thing that pops off the charts is that the program becomes a progressive one. That means the trough that blasts into the West doesn't stay there, as the trough that came into the East with Sandy more or less has for the better part of the past 10 days. Instead, that particular feature wastes no time moving through the Rockies and across the Plains. Now, with downstream ridging showing up over the East Sunday into the beginning of next week, and more upstream disturbances ready to carve out another trough for the West later next week, this trough will be forced through the pipeline, giving it few options. In other words, it will be forced to take the path of least resistance, which will be over the top of the eastern ridge. In the end, that means it will beat it down, but not necessarily replace it. Look at the projected height anomalies Saturday morning:

    Compare that to the forecast for Tuesday morning:

    The trough weakens considerably! That also means the very cold air diving into the West and Rockies this weekend will lose its punch coming east behind the front, with far smaller departures on tap for the mid-Atlantic and Northeast during the second half of next week.

    The other thing we'll have to watch carefully for with this weekend storm will be the threat of severe weather. There will be so much warmth ahead of the front, along with plenty of time to drag a lot of moisture from the Gulf of Mexico to meet the front, that severe weather is almost guaranteed. There may be a little Saturday night over the mid-Mississippi Valley and into the central Plains, but it should become much more prominent Sunday and Sunday night into Monday from Texas northeastward into the Ohio Valley. A prime example of this is the late Sunday night forecast from the GFS:

    Severe weather is less likely Tuesday east of the Appalachians but is not out of the question.

    After the front passes, we'll again shift our focus back to the West Coast for the next trough, one that doesn't look as if it will have nearly the same amount of cold air associated with it, but could still produce a decent amount of rain and possibly more severe weather for portions of the central and southern Plains all the way to the Ohio and Tennessee valleys during the second half of next week.

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

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