A bit of a false start…

In the past week, some significant early season snow has fallen over portions of the western U.S. and far western Canada.  The season is off and running…at least for now…as Wolf Creek Pass in southern Colorado will open this weekend with limited terrain.  I wish I could say that it is a sustainable plan going forward, but unfortunately, the weather pattern that brought the early snow is breaking down and not locking in.  Here is a look at the jet stream pattern that lead to much of the western snow earlier this week…

On this map from Tuesday morning, the dark blue feature in the west is a deep upper level trough where cold air pooled after travelling south from Canada.  The counter clockwise flow around the center of circulation over northern Arizona dragged the cold air southward and mixed it with moisture pulled off the Pacific to provide the ingredients for Wolf Creek’s snow.  The high elevation of the ski area (10,000+ feet) in the San Juan Mountains helped, too. The result was 14 inches of snow…enough for the groomers to work with so some early turns will be possible this weekend.  The other notable feature on the map is the strong ridge that covers much of the eastern half of the continent.  Ridges are warm and late September and the first half of October have been a classic case of “endless summer” east of the Mississippi.  Heck, I haven’t even heard of any frost yet, let alone snowflakes.  

The pattern is going to change this weekend, however.  First, it is going to become more progressive.  That is, the troughs and ridges will be moving along across the continent.  For the most part, the jet stream has been in a stagnant mode for the past several weeks.  I would love to tell you that the ridge is going to break down and go away, but unfortunately, it is going to migrate northward in Canada.  That will allow troughs to cut underneath it and move across the U.S., with each trough bringing along a shot of cooler…not colder…air with it.  When the troughs pass through the West, the air will be chilly enough for high elevation resorts to pick up some additional snowfall, but the air masses just won’t be cold enough to generate snow or snowmaking temps further east.   And that is where the position of the migratory ridge becomes important.  As I indicated earlier, ridges support warmer air masses, and with warm anomalies headed for central and northern Canada, the process of stockpiling early season cold will become more difficult to start.  This map of 5,000 foot temperature anomalies, valid on the 24^th, illustrates this issue.

The temperatures at 5,000 feet are an effective proxy for surface temperatures in the forecasting world, and you can plainly see that Canada is projected to be blanketed with (relatively) warm air later this month.  You can also see a cool swath over the East where a trough will be passing through, but again, it won’t be cold enough to jump start the season.  This is not a long term issue, though.  We just have to give the increasingly longer nights a chance to cool things down in the prime source region for U.S. cold and we will be starting the process from a warmer baseline this season.  I am still bullish on November, based on analog years I have identified.  I will delve into those in my next installment.  Until then, patience is a virtue.