Snow Report

I was able to get up this morning for a quick lap on the Collins glacier to check out the snow situation.  

My ideal first tour of the year is a mild, bluebird powder day.  That's not what I found this morning.  For a while, skinning up above the Watson Shelter, it was snowing hard, the snow guns were blasting, and the wind was roaring down the mountain in my face.  I found myself skiing up with the hood of my shell up and fully zipped.  Welcome to winter!

The wind was primarily a blessing, as it smoothed things out and made for good skiing in places.  It was a curse in a few others, but one can't complain.  The snow situation is better than I expected a few days ago before the weekend storm. 

Automated observations from the Alta Collins observing site suggest 4" of low-density snow fell this morning.  The gauge measured water equivalent is almost surely too low as is often the case when there's strong wind and low-density snow, but using the gauge measurement yields a water content of just under 3%.  

There will be a few snow showers this afternoon and possibly in the early evening.  Then we have a break until late Friday night or early Saturday morning when the next front approaches.  The early part of the storm Friday night looks to be a good producer for the northern Wasatch, although everyone will be getting something.  Mean water equivalent and snowfall from the SREF for the Friday night-Saturday storm is around 0.75"/13".  As was the case for last weekend's storm, the NAEFS is more enthusiastic, with a mean of about 1.75"/24".  The GFS is around .78"/10".  

Let's keep expectations low and hope for another overproducer.  Low expectations are the key to a happy life.  

A Well-Deserved Overproducer

After months of below-average precipitation, extreme heat, coronavirus, earthquakes, and political stress, Mother Nature finally delivered an overproducer for Utah skiers. 

Observations from the Alta-Collins site were a little flaky yesterday, but total snow depth peaked at 23", which is a reasonable guess for new snow amount.  Water amounts, which include the period prior to the one presented below, were around 1.75".  

I suspect we did better than that as the Collins gauge typically exhibits undercatch and underreporting of precipitation.  The Snowbird SNOTEL is up about 2 inches since Saturday afternoon, for example.  Despite my forecast, people were out skiing, with one report to the Utah Avalanche Center as I write this early Monday morning.  

Most impressive to me was the productivity of the storm from early Sunday morning through Sunday afternoon.  There was a lot going on, so it is impossible to generalize they day meteorologically.  I will, however, cherry pick one period from yesterday morning during which things were lighting up nicely in the southwesterly flow over Mt. Timpanogos and Lone Peak.  During this period, the Salt Lake Valley was dry (that changed eventually).  

I remain encouraged by the forecast with some periods of snow possible this week and then the potential for a more significant storm next weekend.  

Keep your fingers crossed and your friends socially distanced. 

Changes Are Coming

Forget about the Presidential election.  Changes are coming to Utah weather, so start looking at forecasts instead of vote counts.  Indeed, there's plenty to hope and argue about in the forecast below.  

I'm having some software problems this morning, so apologies for the garish colors in the loop below which shows either radar or modeled precipitation and the 500-mb (upper-level) flow pattern from 1200 UTC 5 November (5 AM MST Thursday) through 0600 UTC 8 November (11 PM MST Sunday).  The pattern is one that features what we call a "digging" upper-level trough.  That's a trough that instead of moving eastward, moves equatorward and amplifies.  

Really, that's not a best-case scenario for snow in the Cottonwoods for a few reasons.  One is that the "dynamics" associated with the upper-level trough pass to our south.  Another is that the flow stays more southerly or southwesterly.  

However, this is a deep, cold, unstable trough.  Although it's not an ideal situation, it is going to give us more precipitation than we've seen around here in some time.  

In the interest of time, I'm going to summarize the situation through the weekend using a time-height section (see Forecast Tools: The Time-Height Section for more information).  The one below shows how wind (barbs), relative humidity (color fill), freezing level (blue line), and a thermodynamic quantity known as equivalent potential temperature that combines temperature and moisture (back contours) evolve over time.  By convention, time increases to the left not right.  I've identified four key periods with colored boxes.

In the first (brown box), strong southerly flow predominates with low relative humidity at low levels, high freezing levels, and high relative humidity at upper levels.  This period, which will predominate today and tonight, will be windy and mild with dangerous fire-weather conditions (the National Weather Service has issued a Red Flag Warning for this period for all of western Utah including the Salt Lake Valley).  

Tomorrow morning and early afternoon (blue box) will be a transition period with perhaps some fits and starts of precipitation at times.  Freezing levels will lower slightly, but snow levels will be fairly high., perhaps near 9000 feet at 5 AM and lowering to 8000 feet in the early afternoon.  

Precipitation will increase and temperatures will lower later in the afternoon or in the early evening as cold air moves into northern Utah (purple box).  Expect some stronger showers and there's even the chance of a thunderstorm.  Wouldn't that be exciting! 

Later Saturday night and Sunday (red box) we have a period of post-frontal instability.  Unfortunately for the Cottonwoods, the flow never comes around to northwesterly, but remains predominantly southerly to westerly.  Still they will get some snow.  

Let's look at a few numbers for Alta-Collins (9700 feet).  Through 5 PM Sunday the NAM is producing 0.67" of water and 6" of snow.  The GFS, which is typically wetter (and often too wet), is much more enthusiastic and produces 1.77" of water and 23" of snow.  I don't have precise numbers from the ECMWF, but it's around 1.2" for the same period.  

If we look at the SREF ensemble, 5 PM Sunday equates with 09/0Z in the plumes below.  The range for snowfall by that time is from light accumulations up to about 20".  That's a big range, which reflects uncertainty in the track of the upper level flow and the areas of precipitation accompanying it.  

In contrast, the NAEFS ensemble members are skewed to higher numbers.  Again, looking through 00z 09-Nov, they are putting out 0.5 to 2.5 inches of water and 9-40" of snow (I've thrown out the highest and lower members for the snow range range).  

My view of all this based on the large-scale pattern and potential for instability is that the SREF is probably too pessimistic and the NAEFS is probably too optimistic.  I would probably throw out the lowest SREF members and the highest NAEFS members and lean toward 0.5-1.0" of water and 6-12" of snow at Alta-Collins for the period ending 5 PM Sunday.  I think to do better we will need something exciting to happen, like a really strong period of precipitation as the cold air moves in or behind the front.  

Thus, I'm not expecting to be skiing this weekend.  However, if you look at the NAEFS forecast above, there are chances for more precipitation later in the forecast period and the extended beyong that is suggestive we will continue to see action.  

Keep your fingers crossed and hope that this transition to a colder pattern also delivers the goods.  

More Wavering on Storm Certainty

Here we are again with a potential weekend storm in the future.  Assuming the apocalypse doesn't happen in the wake of the election, will you be skiing this weekend?

Well, people are skiing now on the lower portion of the "Collins glacier", but will there be enough natural snow to ski this weekend?

My view is probably not, although we're likely to get more snow than we've seen from the disappointing storms of recent weeks.

The situation this weekend is different than those storms which passed largely to our north.  For this weekend, we are dealing with a trough that is going to "dig" into the western United States and possibly the southwest United States.  Additionally, there is a second trough that moves into the western United States behind it, leaving much of the western United States in the grips of a deep, cold, upper-level trough.  This can be seen in the GFS forecast below.  

The good news is that it's going to get cold and it is going to be unstable.  The tough part about this situation is the "dynamics" of the storm could bypass us to the south, the flow might not be optimal for enhancement in the central Wasatch, or we simply might not get a juicy piece of the flow while the trough is overhead.  

One the other hand, we could get one or more of those things.  

If we're talking about building a snowpack, the water equivalent of the snowfall is far more important than the snowfall amount, so let's start by looking at the the downscaled NAEFS water equivalent forecast for northern Utah through 0000 UTC 10 October (5 PM Monday).  The average water equivalent produced by the 52 NAEFS members is between 1 and 2 inches for most of the upper-elevations of the northern and central Wasatch (top left), with >70% of the members producing at least an inch (middle left).  A relatively small number of members go for more than 2 inches in the central Wasatch (lower right).  

If we convert to snowfall amount, the ensemble mean accumulations are around 18-25" in the upper elevations of the central Wasatch and more than 24" in a few places in upper Little Cottonwood and the northern Wasatch (center top).  Odds of > 24" are 30-40% in the highest elevations of the central Wasatch.  

Looking specifically at Alta Collins, 50 of the 52 members produce 0.5" of water or more for the entire period.  The bulk of the members are between 0.5 and 2" of water.  For snowfall, the range is large, with a mean of about 22 inches and most of the members falling between 10 and 30 inches.  

That sounds exciting, but the higher snow totals reflects the relatively high snow-to-liquid ratios (i.e., low density snow) our algorithm anticipates for much of the storm period (see grey region in lower right panel above).  My view is that the odds right now favor something in the 0.5 to 2.0" of water range, which is good, but not a game changer.  On the low end of that it's almost useless, on the upper end it starts to get me interested with a little help from the snowguns for a skin up Collins.  Although it is not out of the realm of possibility that we do even better, right now the models are sending too much of the dynamical part of the storm to our south.  We either need that to change or the post-frontal crap shoot to come through to give us a big orographic or lake-effect storm period.  That's not impossible, but I'm not counting on it.  

If we end up with some but not enough, don't despair.  There may be some more opportunities next week, although I don't like to place my bets on such long forecast lead times.  

25 Years at the U!

This week marks my silver anniversary at the University of Utah.  Twenty-five years ago we left Seattle Washington, drove across Snoqualmie Pass into the dry, western interior, and arrived in Salt Lake City a day later to a new home and a new life. 

The U has been a great home for me.  I was as inexperienced as they come as a new professor, having just finished my Ph.D. a few months earlier.  One has to wonder what they were thinking hiring me.  I didn't really know what I was thinking when I took the job either, but I got good vibes from John Horel, a professor in what was then the Department of Meteorology, that he would be a great mentor and indeed he has been for 25 years.  John was the best friend and mentor I could hope when I was as a young professor and and remains so as we age into obsolescence.  

There have been a lot of highlights and a few lowlights in those 25 years.  John and I contributed to weather prediction efforts for the 2002 Olympic Winter Games, John leading the development of MesoWest and observing systems at the venues, while I led the numerical weather prediction team.  As part of the effort, I attended and learned about weather support for the 1998 Nagano Winter Olympics and the 2001 Alpine World Championships in St. Anton, Austria.  

Utah Nordic legend Dave Hanscom and I at the Snow Harp Cross Country Venue,
Hakuba Valley, Japan, 1998.

I cannot tell a lie.  Skiing was involved, although there was some work too!  Following the 2002 Games, I've been able to contribute to some other Olympic forecast efforts, most recently traveling to Beijing to contribute to workshops and weather forecasting and monitoring efforts for the 2022 Winter Olympics.  

My extended forecast for those games.  Cold and windy, especially in the mountain venues, with little snow.  Heads up to journalists to pack warm if you're heading into the Beijing area mountains for outdoor events.  

I've also been able to participate in several field programs examining winter storms or mountain weather phenomenon.  In 2000, we somehow convinced NOAA to bring one of their P-3 Hurricane Hunters to Salt Lake City to fly through winter storms in the Wasatch Range.

More recently, I was able to have a homecoming of sorts to examine lake-effect storms on the Tug Hill Plateau during the OWLeS field campaign.  

Photo Credit: Ted Letcher

Of course, the best highlights of 25 years at the U are the people I've been able to work with.  This includes many great students, undergraduate and graduate, faculty, and staff, as well as friends and collaborators at the National Weather Service, especially Larry Dunn, who is now retired, but continues to question everything I do on the skin track or hiking trail.  

The job is not without its challenges.  My dream would be to do what I'm doing for a while longer, but without having to write another proposal.  If you can help, give me a call!

November 1st Ski and Hiking Report

 November has arrived and expectations for skiing are climbing rapidly.  

There's virtually no natural snow (more on this in a minute), but the hiking right now is fantastic.  Beautiful skies, few people, ideal temperatures.  Here's a view of Mt. Superior from Flagstaff around noon today.  

As far as skiing goes, the Collins glacier doesn't go continuously yet.  The lowest 500 vertical feet or so to about 2/3 of the the way up to the angle station was being skied by some today.  Above that, there are segments of man made.  

Although proposals for improving traffic in Little Cottonwood Canyon get a great deal of attention, UDOT has been making substantial changes to their avalanche mitigation infrastructure over the past few years.  Most recently, they've been installing Wyssen Towers in many of the avalanche paths above the Town of Alta.  

Here's a closeup of one on the Flagstaff face, with the remnants of the Albion glacier in the distance.  

The Wyssen towers reduce the number of Howitzer shots that are needed in the canyon.  They can be controlled remotely and lower a charge that detonates to trigger an avalanche.  Check out the youtube video below.

I'm quite grateful to have good hiking right now as I prefer that over purgatory, which is where we would be if it was colder and there was low snow cover.  With COVID running rampant, the warmth has also been a plus as we've been able to continue dining outside with family.

Things will, however, be changing late Friday or Saturday (there are differences in timing amongst the various ensemble members) as a deep trough moves through the western US.  It's too soon to start talking details, but it does look like at a minimum it's going to feel wintery next weekend with temperatures cold enough to support snow down to the valley floors.  

Stay tuned.