Winter Continues

 It didn't take long yesterday after the front went through for precipitation to change to snow at my place (5,000 ft elevation).  The photo below was taken at 1:52 PM in the afternoon when lots of big aggregates (combinations of two or more ice crystals) were falling.

Aggregates are common in warm storms because ice is "stickier" at temperatures near 0°C.  

By evening the grass was covered, and by morning it looked like proper winter.  Fortunately, the roads are warm and driving to the office this morning wasn't too difficult despite the snow covered roads.  

As I write this, the radar looks quite active, so I anticipate we will see snow continue along the east bench for at least a couple more hours before the valley precipitation becomes more scattered.  

Meanwhile in the mountains, Alta is closed to uphill skiing. The automatic snow interval sensor at Alta-Collins has been a bit erratic for this storm period, but if I blink and throw out what I think is questionable data, it looks like they got 8" overnight Saturday and yesterday and then another 11 inches overnight through 6 AM this morning. So, we'll call it 19".  Total water is 1.6".  I suspect if you are ski touring this morning, you're getting the best of the best when it comes to May skiing.  

The models call for this initial cold trough to move downstream today with a weak ridge moving in this afternoon (emphasis on weak).  That will probably bring a lull to the action in the afternoon with rising temperatures in the valley likely resulting in the snow turning to rain at some point today, even on the benches by mid afternoon.  A wildcard is the possibility of a thunderstorm, which might push the snow levels down temporarily again.  

Then another short-wave trough comes in tonight and lowers snow levels again to near bench level, with another trough dropping down into northern Utah Tuesday night.  From 9 AM this morning to 5 AM Wednesday morning, the GFS puts out another 20" for Alta. 

Winter continues.  

A BIG MAY STORM

This is a blog post that deserves all caps.  The models continue to advertise a major May storm cycle that will bring substantial snowfall to the mountains of northern Utah. 

As I write this on Sunday morning, the south winds are blowing and temperatures in the Salt Lake Valley are in the 60s.  

But everything is about to change.  A look at the latest observations shows northwesterly flow and colder air to our west.  Along I-80 at at Knolls it's 43°F.  

The front will likely push through the Salt Lake Valley from about 9–11 AM this morning.  Precipitation will also spread across the area.  The coldest of the cold air arrives tonight.  The GFS shows unstable, northwesterly flow tomorrow morning with 700-mb tempeatures around -8°C.  In January, that would probably mean wet snow on the valley floor.  In May, it's probably down to near bench level.  Don't be surprised to see flakes late today or tomorrow.  

For the mountains, the models are putting out some big numbers.  The 6Z HRRR forecasts 19" of snow for Alta through 0600 UTC (0000 MDT) Tuesday.  

The GFS is locked in with similar numbers through that time.  Additionally, it keeps us in a cold pattern through Wednesday with a series of systems moving through and pushing the storm totals to about 3" of water and 40" of snow by Wednesday.  

These are serious May numbers.  I'll add that the forecast above also shows northwest winds on Monday on Mt. Baldy of over 40 mph.  Real winter, with real-winter avalanche conditions, and the possibility of a rapid change to wet-snow avalanches conditions should the sun appear.  

Let's be careful out there.

Good Skiing Early Next Week?

Forecasts for late Sunday and early next week are, how shall I put it, interesting.  Both the GFS (below) and the Euro are bringing a deep upper-level trough and strong cold front into northern Utah on Sunday afternoon.  

Then, in the wake of that system, there's a prolonged period of moist, northwesterly flow with a couple of weak disturbances thrown in to help juice things up.  Below is the forecast for 1500 UTC (9 AM MDT) Monday showing heavy orographic snow showers over the Wasatch.  

The forecast 700-mb temperatures at that time are also about -7°C, which could drop snow levels to near the benches.  

For upper Little Cottonwood, the latest GFS is going off and produces 3" of water and 35" of snow for Alta-Collins from around 11 AM Sunday through noon Tuesday.  

That is, however, an upper-end forecast, topped by only a few members of the downscaled NAEFS.  the NAEFS mean is closer to 2" of water and a bit over 20" of snow.  There's also a good deal of spread, indicating a wide range of possible outcomes. 

 

That said, it looks like cold air is coming and with it the potential for significant mountain snow.  We'll see if things come together for this early May storm.  

Some Oddities About This Deluge

Impressive rainfall numbers are coming in from this latest storm period.  Total accumulated precipitation since very early Friday morning (~5 AM MDT 26 April) is now over 1.1 inches at the University of Utah.

A look at accumulations for the Salt Lake Valley region shows the largest accumulations in the Tooele Valley and Magna areas and secondarily along the east bench of the Salt Lake Valley.  Water equivalent totals in the central Wasatch are actually lower than at the high precipitation sites along the east bench. 

If you are wondering, my guestimate for Alta-Collins based on automated measurements is about 6 inches of creamy snow from 0.85" of water.  I suspect snowfall amounts at the base are lower given that some of the precipitation may have fallen as rain yesterday.  

Let's talk about some of the oddities of what is happening this morning.  We operate profiling radars in the Salt Lake Valley (at Highland High) and at Alta.  Each peers up through the storm and we generate time-height sections with them showing the evolution of the vertical structure of the storm.  In the 3rd row below are profiling radar time-heights from Highland High showing nearly continuous precipitation over the three hour period ending at 16:40 UTC (10:40 AM). In contrast, at Alta, there was only a brief period of precipitation.  

So if you drove up to Alta expecting dumpage, I suspect you were disappointed.  Hopefully the cream on crust skied well.  

So, my back yard this morning looked like coastal northern California.  Foggy, rainy, and green.  The deer are laying low.

But up at Alta, you could actually see blue skies at times this morning.  The web cam image below was taken at 7:42 AM MDT.

Of course, the clouds appeared to move in and out and you could have been in the ping pong ball at times.  Still, a different world up there than in the valley.  

What also caught my attention was how shallow the radar echoes were above Highland High.  For most of the morning they have been below 2000 m above ground level or about 3350 meters above sea level.  That's just under 11,000 feet.  That makes it a very shallow storm, at least in the Salt Lake Valley (it may be deeper to the northwest where echoes in the KMTX radar are stronger.  Temperatures this morning at 11,000 feet were around -5°C.  At such temperatures, it is hard to get ice to form.  There is a decent chance that the rain this morning in the Salt Lake Valley was produced by warm-rain processes.  Instead of there being ice crystals that grow and then fall out and melt on their way to the ground, as often occurs when it rains around here, cloud droplets colliding and coalescing was likely the main pathway for generating rain drops.  This is hard to do over continental interiors.  It's the sort of thing that one typically sees in coastal areas (e.g., northern California) or the windward side of the Hawaiian Islands.  

Anyway, that's my hypothesis.  I can't rule out the possibility that the storm was deeper than indicated by radar, but my impression, based on the droplet characteristics, that we saw warm-rain processes predominating this morning.  I await additional observations from you readers.  

Big Ups for Atmospheric Sciences at the U

Faculty from the University of Utah Department of Atmospheric Sciences won two major University-wide awards this year with Dr. Kevin Perry Receiving the Presidential Societal Impact Scholar Award and myself a Distinguished Teaching Award.

Kevin's award stems from his work illustrating the climate and health effects of dust from the exposed lake bed of the Great Salt Lake.  This is a project born from intellectual curiosity and personal drive and in it's early stages was largely unfunded.  Kevin rose a fat bike across the exposed lake bed, collecting samples and illustrating the toxic composition of dust from the lake bed.  This has helped to identify a critical health issue and motivate efforts to save the Great Salt Lake.  

You can read more about the Kevin's efforts in this 2019 article from the Salt Lake Tribune.  

I was deeply honored to receive a Distinguished Teaching Award and would like to thank everyone who has read this blog, attended one of my public talks, or taken one of my classes for motivating me to try and become a more effective science communicator and teacher.  When I started this blog in 2010 (yes, it was a long time ago), I had no idea where it would lead.  It eventually led me to publish Secrets of the Greatest Snow on Earth and develop an online, general education science class of the same name.  That class now has almost 500 students.  Who knew so many University of Utah students were interested in snow?  Well, I confess that I had a pretty good idea that a science class built around snow and skiing might be popular, but it took a village to build a great online class.  Much thanks to the colleagues and consultants who I've worked with, University of Utah Digital Learning Technologies, University Connected Learning, Teaching and Learning Assistants, and many others.  

We've Created a Monster

Last Week, the Kem C. Gardner Policy Institute at the University of Utah released a detailed fact sheet highlighting the economic contributions of Utah's ski industry.  If it seems like the Utah ski industry has changed dramatically in recent years, this study largely confirms it.  A few interesting tidbits.  

Skier days have really taken off since 2020/21 with each year since setting a new record, reaching 7.1 million in 2022/23.  And that 7.1 million was reached with Little Cottonwood being closed by avalanche hazard for the latter part of the season.  If it seems like there are more people at the resorts than there used to be that's because there are.  

Where did all these skiers come from?  During the 2022/23 season, 44% were from Utah.  The rest came from all over the place.  Want to blame California?  They are the biggest non-Utah source, although they represent only 8% of skiers.  Colorado is good for 2%.  I think they come for the snow. 

One graph examined the relationship between annual snowfall (apparently at Alta) and skier days.  I look at this chart and I see the variability caused by seasonal variations in snow being somewhat small through about 2017/18 when growth takes off and dominates.  

There was no attempt to look at backcountry skiing.  Although the number of skier days is probably a factor of 10 or more smaller, I suspect the growth rate is even larger than the skier days at ski resorts. 

All is not rosy of course.  Access has changed.  Reservations and parking restrictions are now the norm.    Transit options remain limited.  As a friend of mine put it, "we've created a monster."  

Where do you think we will be in 2030?  How about in 2050 when Utah's population is projected to be 5 million compared to about 3.4 million today?  Remember, all of this will be happening in a warming climate.

You can access more at https://d36oiwf74r1rap.cloudfront.net/wp-content/uploads/2024/04/SkiIndustry-FS-April-2024.pdf