Colder, snowy pattern evolving coast to coast…

As we hit the holiday season, the weather pattern is changing to one that will soon be dominated by colder than normal air.  Cold air has been in relatively short supply for a couple of weeks now, but in the past week, a series of troughs have descended into the West, leading to several sizable snow events that have given the season a badly needed jump-start in the coastal ranges with lighter but helpful snow further inland.  Elsewhere, snowmakers have had to pick their spots for cranking out crystals, and trail counts have been creeping upward in the Midwest, Northeast, and central and southern Appalachians.  What is needed is a jet stream pattern change that taps more cold air from Canada and thankfully, here it comes.

Here’s the current state of the jet stream…

There are several features of note on this map, which is valid on Friday the 17th.  First, there is the broad ridge over the eastern U.S., with the center of the feature the closed circle that you see north of the Bahamas.  This ridge is a common feature in a La Nina winter…when it is strong, as is the case now, mild air spreads north.  When it is suppressed, cold air penetrates further south from Canada.  There are two troughs over the western half of the country…one over the Dakotas and the other over Baja California.  Both were responsible for snow earlier this week.  The northern feature will help to break down the ridge and produce a light to moderate snowfall over the interior Northeast this weekend.  The last item is the ridge over Greenland and the trough south of it, over the waters of the Atlantic.  This couplet forms a classic “Negative NAO”, or North Atlantic Oscillation.  When the NAO goes negative, it blocks the progression of jet stream features over much of North America.  Typically, a negative NAO leads to a persistent trough over the eastern half of the U.S. and that is where we are headed.

Here is a forecast for the jet stream on Christmas Eve, which I generally agree with…

You can see the negative NAO ridge/trough couplet top right.  The troughs over the east coast AND west coast hold the promise of colder weather and natural snow in both regions.  The ridge over Alaska, with its clockwise circulation, will tap into the very cold air stored over the northwestern part of the continent and send it further south.   As the holiday week progresses, the Yukon connection will bring about a trend toward colder temperatures from the upper Midwest into the East, all the way down into the mountains of North Carolina.  The jet stream setup that you see on this map is just about perfect for benefitting resorts coast to coast…those trail and lift numbers should be on rise from this weekend right through the holiday week.  Here’s a look at snowfall predicted through Christmas Day…              

During the holiday week I expect the snowfall numbers to increase in the East and spread down the Appalachians, in anticipation of the presence of the trough that will enhance snowfall opportunities.

Here are regional highlights…    

Northwest U.S./Western Canada:  Pattern favors a trough offshore for a while…leads to frequent episodes of moderate/heavy snow.          

Sierra:  Quiet weekend but significant snow returns Tuesday-Thursday next week.  Another storm around Christmas Day           

Rockies:  Northern resorts in a good position for snows in the next week…south of I-70 best chance will come late next week 

Midwest:  Upper trough, Clippers, lake effect, and snowmaking keep trail counts growing through the holiday period 

Mid Atlantic/Southeast:   Productive snowmaking next week…natural snow a good bet Christmas Week.        

Northeast/QB:  Moderate snow this weekend north of I-90 in NY/NE.  Snowmaking and natural snow push trail counts up going forward through the holiday 


  1. Paul Forlenza says:

    Great description of weather coming our way (NE). Would be useful to know what the colors mean in the last graphic. Thanks.

  2. Paul Forlenza says:

    Also, that white space in central Vermont has been a pattern for several years. I live just to the west of the green mountains (to the west of Sugarbush which is on the other side of Lincoln Mountain from me). This is an area we call the “snow desert”. Snow seems to fall north of Route 2 and south of Route 4 (both run east to west across the state). In between is the “snow desert”. Any thoughts why?

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