Cold air supply growing…

Before I look forward in this discussion, let’s look back. October was a very warm month relative to normal across the country, in large part because a sizable upper level dome of high pressure stretched across Canada and the northern states. Early snow cover over northern Asia and Canada are typically harbingers of a fast start to our winter sports season, and although Russia stocked up with snow early and often, the upper ridge over Canada meant that a buildup of early season snow cover there was a non-starter. Now that doesn’t rule out a quick start to the season, but it does make it tougher. The good news is that the pattern in the high latitudes has been changing, and snow cover is accelerating. That has led to a rapid buildup of the cold air that we need for snowfalls and snowmaking. Forecasters use temperatures at 5,000 feet as a proxy for predicting surface temps and just a couple of weeks ago, there was a warm anomaly at that level spread out from the Canadian Rockies to the Maritimes. But take heart, the supply of cold is growing and the jet stream mechanism for delivering the cold…upper level troughs…have started to appear. Here’s proof. First, the jet stream setup for 11/13…

That large blue ball of yarn centered over the western Great Lakes is a deep trough that has delivered snow to the northern Plains this week, and it will generate lake effect and mountain snow showers as it pivots east this weekend. It has the goods in terms of cold air, as you can see on this map of the temperature anomalies at 5,000 feet.

In November, we find smaller “chunks” of cold air than we will a month or two from now, and that is why you see orange to the west and east of the cold shot in the middle of the continent. That tells me that the pattern will be rather changeable through the end of the month, with the cold shots alternating with brief warmups…very typical for a transitional month like November. As time goes on, the supply of sufficiently cold air for snow will grow, and we can see that if we look at the 5,000 foot anomalies for the Sunday before Thanksgiving…

Notice that is appears as though the Lakes and East will be well supplied with cold air and the next cold air mass will be linked to the piece over the eastern third of the continent. The purple color you see over NW Canada suggests that the cold will be deepening, as well. So, it appears to me that the resorts in the Great Lakes and East will have opportunities for snowmaking leading up to Thanksgiving, and the air masses will, at times, be cold enough to support natural snow. In the West, more of an upper ridge will be in place and that will limit the opportunities for significant Pacific storms to lend a hand. The northern Rockies will catch a glancing blow from the NW-SE push of cold air masses, and that could generate some snowfall in the next couple of weeks. Let’s break it down by region…

Northwest U.S./Western Canada: Best shot at snow in the next week is higher elevation slopes in B.C. NW U.S. prospects very limited for now.

Sierra: West coast upper ridge keeps it mild and dry until further notice
Rockies: Glancing blows from systems diving into central/eastern U.S. trough brings light snow every few days to northern resorts. Central and south quiet for now.

Midwest: Upper trough, cold shots, and lake snow become commonplace up through Thanksgiving. Solid prospects for early openings.

Mid Atlantic/Southeast: Enough cold air penetrates from the north to get snowmaking started at times over the next couple of weeks.

Northeast/QB: Good snowmaking opportunities will develop leading up to Thanksgiving. Several shots at mountain snow, as well.


  1. Thanks to Herb for his input. From a west coast slider that also started in the early 1950s

  2. Richard Kavey says:

    Herb, Thanks for your most excellent forecasts!

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