Weekend Storm to Deliver Cold Air, Snow | NECN

Weekend Storm to Deliver Cold Air, Snow

A storm next weekend will bring snow to some parts of New England, possibly heavy in the northern mountains.

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    In this post...

    • Blockbuster regional storm for the Northeast quite unlikely (not impossible).
    • Coldest air of the season quite likely.
    • Some snow quite likely, particularly in the North Country.
    • Heavy mountain accumulations possible.
    • Wide range of solutions - too early for exact accumulations to be responsibly given.
    • Some flurries or snow showers not impossible farther south into Central or Southern New England at some point this weekend, depending upon the setup.

    An intense upper level disturbance will dig out a large "trough" in the jet stream over the Northeast United States at the end of this week, thrusting the coldest air of the season into New England for both weekend days, when high temperatures are likely to remian in the 40s for many - and even the 30s for some of the North Country. Remember that the jet stream winds are the fast river of air aloft that steers storm systems and separates cold air to the north from warmer air to the south, so a trough, or dip southward, in the jet stream, implies a large shift of cold air southward, and this is what opens the door to cold air from Canada for New Englanders.

    With any passage of a large amount of energy and intrusion of cold air aloft, the meteorologically-minded must be mindful of mayhem, and this setup is no exception. Note, in the plot of atmospheric energy, below, valid Friday evening, the strong energy (represented by the yellow/orange coloring) moving southeast across Michigan and the Great Lakes region, while another bundle of energy scoots east of the Eastern Seaboard, over the Gulf Stream.

    Fb1

    The "northern stream" energy, dipping south from Canada, is providing the cold air, and as noted in Tim Kelley's blog post Sunday, is actually a piece of the remnant former Hurricane Ana, traversing Canada and grabbing a bundle of cold air along the path. The energy over the Gulf Stream is found in the "subtropical jetstream," and represents a substantial amount of available moisture. When the cold, the energy and the moisture phase together, a major storm results. That merger is expected to happen this weekend, but looks like it happens too far east for a big storm for most of New England, though the mountains may be an exception to that.

    First, on the big picture, note a comparison, below, of mean sea level pressure (barometric pressure), illustrating where low pressure (storms) and high pressure (fair weather cells) are located. The first image is an average plot of 21 different American guidance products, and the second is an average plot of 51 different European guidance products. Notice, first and foremost, how rather similar they are to one another:

    American (GFS) 21-member average sea level pressure:

    Fb2

    European (ECMWF) 51-member average sea level pressure:

    Fb3

    Neither of these solutions are the be-all and end-all of the weather forecast, and you can bet that each of the members averaged above includes widely varied solutions. That said, we surely can take away a major point that - at least as of this Tuesday morning post - there is actually tremendously good agreement on any big storm center cranking up well east of New England.

    While a storm cranking up well east of the region takes a region-wide blockbuster off the table of most likely possibilities, there are some points of interest. First, in the images above, there certainly is a difference in the position of the storm center forecasts, implying there is still some variability to where the strong low pressure center actually ends up. Next, notice that both solutions imply a strong, northerly wind flow. This particularly sets off these flags:

    1. Cold air will rush into New England next weekend, and looks intense enough to keep high temperatures in the 40s south and 30s north both Saturday and Sunday.
    2. A northerly flow with abundant lingering moisture in the atmosphere the the core of Northern stream energy moving directly overhead implies an excellent setup for "upslope" snow showers and squalls with the *potential* for significant accumulation in the high terrain of Northern New England Saturday into Sunday.

    In fact, check out the snowfall forecast through this coming Sunday night, from that same average of 21 different American (GFS) guidance products - amounts are fairly low, but at this stage of the game, that's to be expected with so much variance among each of the 21 members - the takeaway point is the North Country is targeted for accumulating snow:

    Fb4

    What starts to get really interesting is when you break apart individual members to examine the range of possibilities. "Operational" guidance assists in doing this - providing one, determined forecast of what may happen. The danger is that they can be wholly inaccurate. The benefit is they can help to identify the range of potential scenarios. Consider some of these, but please remember - I'm not actually forecasting any of them to occur - I prefer a general pattern of North Country snow outlined above, and maintain it's too early for exact amount forecasts, but the potential exists for half a foot in some mountains.  Nonetheless:

    The Operational GFS (American) guidance, with nearly half a foot in Western Connecticut:

    Fb5

    The Operational ECMWF (European) guidance, with half a foot in Vermont's mountains:

    Fb6

    The Operational GEM (Canadian) guidance, with a foot in the Maine mountains:

    Fb7

    And - the average of several versions of the above GEM guidance - wow. Notice that the average totally wipes that snow away when you consider all the possibilities:

    Fb8

    So, if we're going to be analytical, scientific and non-alarmist, steering away from hype, here's what we have:

    • Blockbuster regional storm for the Northeast unlikely.
    • Coldest air of the season quite likely.
    • Some snow quite likely, particularly in the North Country.
    • Heavy mountain accumulations possible.
    • Wide range of solutions - too early for exact accumulations to be responsibly given.
    • Some flurries or snow showers not impossible farther south into Central or Southern New England at some point this weekend, depending upon the setup.

    I'll keep you posted, online and on NECN.

    Matt

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