Tag Archive for: US weather

Herb Stevens

The Skiing Weatherman-January 21, 2022

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East stays stormy…snow returns to the West

As we approach the approximate halfway point in the skiing/riding season, the slopes in all regions of the U.S. and adjacent to Canada are in good condition, with the western half of the continent still benefitting from the astounding amounts of snow that fell in late December.  This season got off to a roaring start in the West and a sluggish one in the East, but the jet stream pattern that delivers cold and storms has favored the Midwest and East for a couple of weeks now.  A western ridge/eastern trough couplet has dominated, and that setup will remain in place much of the time for the rest of this month.  In early February, a subtle change will lead to a turn to milder weather in the East.  If we look at the jet stream map as this forecast gets underway, we see strong ridging that stretches up to Alaska where the clockwise flow around that ridge can tap deep cold air over northern Canada. 

In that position, the ridge is far enough west to allow small packages of jet energy to slide down its eastern flank and bring some snow to the inland ranges of West.  Not major snow, due to the lack of a direct tap into Pacific moisture, but after lots of bluebird days of late any new snow is very welcome.  The coastal ranges from B.C. down through California will be kept rather dry by the eastern flank of the large upper ridge sitting offshore.  The jet level flow along the coast is nearly northerly right now, so the disturbances will be able to dive all the way to the Mexican border, which would bring the resorts south of I-70 some light snow this weekend…the fast movement will limit the input of Pacific moisture, but the “freshies” will do a nice job of softening the surfaces a bit.

As has been the case for the past couple of weeks, the real forecast challenges will come over the eastern half of the country, where the interaction of the northern and southern branches of the jet stream determine the track and intensity of surface storms.  In the Rockies, the track of the storm determines who get heavy snow and who gets light snow.  In the Midwest and East, it determines much more, with sleet, freezing rain, and plain rain often part of the landscape.  If we look at the Monday morning 1/24 jet stream, we can see a good example of the forecast challenge. 

The systems that swings through the Southwest is headed out to the southern Plains, where it could join forces with northern stream energy moving into Minnesota.  If they phase into one larger trough, another substantial winter storm would impact the Midwest and East.  Just where the two branches of the jet combine will determine whether the surface low goes up west of the Appalachians, just east of the mountains and along the coast, or it stays off to the south.  All three have vastly different outcomes in terms of “who gets what”.   Right now, I favor the two streams staying separate with light snow in the Lakes and Northeast.  This busy pattern will persist until the trough eases west at the end of the month, perhaps supporting a “cutter” low into the Lakes at that time.

weather diagram
Herb Stevens

The Skiing Weatherman-November 12, 2021

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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.