Overexuberant Starting Dates and Splitting Storms

Delays in starting dates for ski areas are in the news.  Brianhead was scheduled to open on November 7 and has pushed their starting date back to November 21.  Solitude was scheduled to open on on Friday (Nov 14), but has pushed it's starting date back to next Wednesday (see this Trib article).  

In my view, this is much ado about nothing.  November is a fickle month.  Sometimes resorts can open, even as early as late October with natural snow as Brighton did in October 2004.  Sometimes we get a cold spell that enables sufficient snowmaking to get some terrain open with limited natural snow.  And sometimes we get a nothing burger.  We're getting the latter this year.  If you get a warm, dry stretch in February, you get a suntan while doing groomer laps.  When one happens in November, you get a delay to the start of the ski season.  

It is true that temperatures so far this November have been warm, with an an average for November 1-12 of 51.7°F at the Salt Lake City airport.  That is the 2nd warmest on record, but sometimes a ranking hides subtleties.  If we look at records since 1929 when observations were first collected at the airport, there have been 8 other Novembers with average temperatures at or above 50°F.  So, this year is warm, but to some degree it is cooked into the cake of weather variability.  Warm dry stretches in November can happen.  

The plot above also shows a great deal of variability as one might expect for a relatively short 12-day period in the late fall.  The coldest November 1-12 was in 2000 when the mean temperature was 32.6°F.  Holy cold surge Batman!  

The linear trend line is consistent with a warming trend as we might expect.  We will see more warm spells in the future and the resorts will find it more and more difficult to open early season terrain with current snowmaking capabilities. Opening a resort in Utah in early November has always been a crap shoot, but the odds will be decling in the future without advances in snowmaking capabilities.  

Looking to the future, the pattern over the next several days is dominated by splitting storms.  Split is a four letter word around here (yes my math is bad), but the reality is that many of our storms split.  The analysis below shows the average 300-mb (jet-stream level) winds during winter in the Northern Hemisphere.  On average, the Pacific jet is strongest in the western North Pacific.  The western United States is at the end of the Pacific jet in what metorologists call the "jet exit region".  On average, the jet level flow over the western. United States is actually relatively weak and this is consistent with the jet-level flow decelerating and splitting.  This is essentially a consequence of the distribution of continents and oceans in the Northern Hemisphere, the distribution of sea-surface temperatures in the North and Tropical Pacific, and the topography of western North America, among other factors.

So, many of our storms split.  The Wasatch Range gets a lot of snow because northern Utah still manages to get some snow from splitting systems, the split sometimes weakens and storms are able to penetrate directly into Utah, and the topography around here, especially around Little Cottonwood Canyon is just damn good at squeezing every dendrite out of winter storms.  

A textbook case of splitting storms is on tap for the next several days.  The GFS analysis for late yesterday morning [1800 UTC 12 November (11 AM MST Wednesday)] shows a full-latitude trough off the west coast (upper left panel) with and accompanying cyclone centered off the coast of Oregon and California (upper right panel).  

Instead of progressing to Utah, the upper-level trough amplifies through 1200 UTC 14 November (5 AM MST Friday), resulting in split flow with one branch of the jet moving across southwest Canada and the other taking a circuitous route around the upper level trough and into southern California (upper left panel).  As a result, the precipitation system moves into western North America in two pieces, one over central and southern California, the other near the Canadian Border (upper right).  

But the GFS forecast calls for things to get worse, at least temporarily for Utah. By 1200 UTC 15 November (5 AM MST Saturday), the southern storm has continued to dig southward.  SoCal is getting the goods, but we're left high and dry.  

Whether or not all is lost with this storm depends a lot on what it does as it drifts downstream and moves across the interior west.  By 0600 UTC 16 November (11 PM MST Saturday), remnants of the system are moving into Utah.  

Forecasts out to 10 days show a lot of splitting storms.  Our snowfall future depends strongly on the track of these storms and their remnants.  Sometimes we can really get a lot of snow from upper-level patterns that meteorologists from other regions think are fairly innocuous.  However, such details are hard to predict and this is why the Utah Snow Ensemble is a junk show for Alta (and northern Utah locations) with enormous spread in total water equivalent and snowfall over the next 10 days.  And that spread is not because there are one or two extremely high or extremely low outliers.  That's actually a fairly even distribution of members producing a total accumulated snow total through 0000 UTC 23 November between 15 and 50 inches.  

So, a lot of uncertainty, but we might frame that a little differently.  75% of the members produce 1.93" of water and 16" of snow through that time and 50% produce 2.5" of water and 32" of snow, the latter on the cusp of rock-ski skiability (I know some of you go out with less).  

So one way to think about this is there's a 50/50 chance we'll have marginal early season skiing next weekend.  I'll let you decide if you want to be a pessimist or optimist about which side we will land on. 

And if you are wondering, yes, this is one of those blog posts that I start and when I get to the end I realize I bit off far more than I can chew!