Evidence of Top Down Mixing

The pollution layer over the Salt Lake Valley remains today (Saturday) but clearly shallowed over the past few days.

The photo below was taken at 0743 MST Tuesday.

 You can compare that with the one below taken at 0745 this morning.

So, some temporary relief in some upper-bench areas.  

On the valley floor, there was also some improvement, with PM2.5 this morning at Rose Park being lower than it has been in a few days.

All of this is evidence of top-down mixing with the pollution being mixed out from the top down.  Sadly, it has not all been removed on the valley floor. 

What remains after today we will probably be stuck with again for a while.

Stirred Not Shaken

As discussed in the previous post, a weak upper-level trough was expected to move over northern Utah yesterday, but it was unclear if it would crack the inversion (I was skeptical).  Indeed, looking at things this morning, I'll call it "stirred not shaken." Impacts on the pollution are varied.  In the Avenues foothills, there was clear improvement and evidence that the pollution is shallower, as sometimes happens in a weak partial mixout event in which things are eroded from the top down.  

On the other hand, a look at satellite imagery shows evidence of fog or low clouds in portions of the Salt Lake Valley, Tooele Valley, and the area from Bountiful to Layton.  Instead of being bright like the mountain snow, the fog and low clouds look grey, which may reflect that it is thin, patchy, or simply mixed with all of the smog that is still stuck on the valley floor. 

Source: College of DuPage.  Image from 1611 UTC/0911 MST 16 Jan 2026.

As I worked on this post this morning, some of these low clouds moved over campus.  

Air quality during this episode has varied considerably during the day.  At Hawthorn Elementary, one can see the PM2.5 levels peaking each afternoon.  Peak values worsen each day through the 14th (Wednesday).  There was slight improvement yesterday.  

Source: MesoWest

At Rose Park, one sees this same behavior, but peak values are somewhat higher and the nighttime declines are not as large. PM2.5 concentrations this morning are just a smidge lower than the previous two days.  

Source: MesoWest

The question now is what will happen this afternoon.  Temperatures this morning are actually several degrees C cooler above the valley floor than they were yesterday.  At about 7000 ft elevation, for example, it's 1.8°C this morning, whereas it was 5.0°C yesterday.  Thus, the inversion is weaker.  This makes it more susceptible to surface heating during the day.  One possibility is that with a bit of surface heating we start to vent the valley floor and we mix out some of the gunk.  A best case scenario is we vent everything.  I think that's unlikely, although perhaps some areas see some improvement.  

Perhaps more likely is that the pollution remains very stingy over and near the Great Salt Lake.  The lake is a bit colder than the surrounding land surface in situations like this and there can be a lens of cold, polluted air that remains entrenched over it.  That cold and polluted air tends to move into the Salt Lake Valley during the day.  Sometimes it mixes out for a bit only to have the polluted lake air push in during the day.  

We will see how this pans out.  Definitely a tough forecast.  Hope for a full mix out.

We Could Be Screwed

Just another day in the paradise that is the Wasatch Front.  The latest west-facing image from the University of Utah shows a blanket of smog over downtown Salt Lake City.  

Source: https://horel.chpc.utah.edu/camera_pages/wbbw.html

It's tough to get above it without going to the mid elevations.  I hiked this morning to the top of the Avenues foothills and it was unclear if I was completely out of it even at 5700 feet.  

Recent station (filled squares) and mobile (filled circles) PM2.5 observations show values in the valley generally between about 28 and 45 ug/m3.  

Source: https://utahaq.chpc.utah.edu/

The threshold for unhealthy for sensitive groups is 35.5 ug/m3, so we are seeing values that are near or above that.  The DAQ sensor at Hawthorne Elementary is at 41.3 ug/m3 as of 2 PM.  

Is there hope for a mix out?  The best chance is probably on Thursday and Friday.  On Thursday there is a weak upper-level trough moving over Utah late in the day in the ECMWF HRES forecast.

In the wake of that system, the northerly flow increases and crest-level temperatures drop to perhaps -2°C.  Perhaps the cooling aloft combined with the increased flow can at least give us a partial mix out, but other models are less optimistic than the Euro and it's possible we're screwed.  The GFS forecast for Friday afternoon, for example, still has a capping inversion based at about 825 mb.  In that case, we probably remain exiled in hell.  

Assuming we don't or only partially mix out, we could see the development of fog and eventually stratus that's elevated above the valley floor.  That will make for even more depressing conditions, but in some of those situations cloud base raises with time and produces a deeper mixed layer at low levels.  There's still pollution, but there's a bit more dilution that helps to moderate the PM2.5 levels (although they can still be hazardous).  

Hope for that partial mixout on Thursday and Friday.  

LCC Is Back (Temporarily)

January 8 marked the first day this season with an above median snowpack water equivalent at the Snowbird SNOTEL.  Hooray.  LCC is back, at least temporarily. The recovery from the storms over the past week in upper Little Cottonwood Canyon has been remarkable.  The skiing yesterday for a non-powder day was really great, with great groomers you could carve the hell out of and an open and well covered (or as covered as it ever gets) High-T providing access once again to "real skiing."  

Although deep powder is the pinnacle of skiing, I always pinch myself on sunny groomer days like yesterday because I didn't know weather and snow like that were even possible when I was a kid in upstate New York. 

Looking down Mambo and remember my roots

Sadly the forecasts are dismal.  I don't know if I've ever seen the Utah Snow Ensemble completely flatlined for a 10-day period, but it is.  

Actually there may be a couple of members in there that produce a skiff of snow here or there as I see a couple of whiskers poking up just a bit in the middle panels, but for all intents and purposes it's over for at least the next week.  The good news is that it's January and between the low sun angle and cool forecast wet-bulb temperatures, Mother Nature won't be spoiling the snow on upper-elevation aspects on the north half of the compass.  The skiing should hold up about as well as it can without a refresh.  

And, given the conditions this year and my plans to be in Austria in a few weeks, I'm looking for a front-side all-mountain ski for groomers and off-piste skiing when it isn't deep.  Although I'm a reasonably proficient technical skier, given my advancing age, I appreciate a ski that doesn't require huge energy input.  If you have suggestions, add to the comments.  

Evidence of a "Warm" Snow Drought

The latest snow observations show very clear evidence of a "warm" snow drought, one in which the snowpack has been strongly affected by abnormally warm temperatures, resulting in a majority of precipitation falling as rain and periods of snowmelt or loss at low to mid elevations.  

Evidence of this warm snow drought is especially clear if one looks at the yesterday's percentage of median 1991–2020 snowpack water equivalent at SNOTEL stations as a function of elevation.  As shown in the plot below, stations below 7600 feet are at 30-49% of median and, as indicated by the red bars, are all at all time minimums for their periods of records (which vary in length but extend back at least 27 years).  

Source: NRCS

In contrast, the percentage of median at higher elevation stations is higher and anywhere from 69–111%.  Yes, incredibly, both the Snowbird and Brighton SNOTELs are now sitting above median.  It's good to be at high altitude in the upper Cottonwoods.  As meteorologist S. D. Green said in 1935: 

"Skiers will eventually find that the…heads of the [Cottonwood] canyons…offer the best skiing to be found in the Wasatch Mountains.”

But if he were alive today, he might instead say:

"Skiers will eventually find that the…heads of the [Cottonwood] canyons…offer the best skiing to be found in the Wasatch Mountains and their advantages over other lower elevation regions of the Wasatch are growing as the climate warms."

But now lets add insult to injury and turn off the precipitation.  The latest model forecasts are pretty much a disaster.  A massive high-amplitude ridge is setting up along the Pacific Coast and looks to starve Utah of moisture.  I am electing not to show the forecasts due to their graphic nature, which some readers might find disturbing.  

SNOWSCAPE2026 Begins

I'm supposedly on sabbatical this academic year, but the reality is that I've been working a ton with colleagues at the University of Utah and institutions planning, preparing, and now executing the SNOWSCAPE2026 field campaign.

SNOWSCAPE is an acronym for the Seeded and Natural Orographic Winter Storms and CAtchment Processes Evaluation Project, with 2026 indicating that it is being held during the 2026 water year (we hope we may be able to do this in future years too).  This is the largest field campaign examining winter storms in northern Utah since the Intermountain Precipitation Experiment (IPEX) in 2000 and also includes a major snow hydrology component.  

SNOWSCAPE is specifically examining winter-storm processes and the impacts of cloud seeding on snowfall, snowpack accumulation, snowmelt, and runoff in Utah's northern Wasatch Mountains and the lower Weber and Ogden basins.  We have established a one-of-a-kind transect of observing sites from the eastern end of the Antelope Island Causeway, over Snowbasin, to Huntsville to document changes in storm characteristics from the Wasatch Front lowlands to the mountain valleys.  Along or near this transect we have weather cameras, precipitation gauges, lidar ceilometers (which measure cloud base and precipitation characteristics), microwave radiometers (which provide profiles of temperature and cloud liquid water), profiling radars, snow-energy balance stations, and streamflow gauges.  We also have an aerosol sampling system at Powder Mountain that is measuring the characteristics of small particles in the atmosphere that can serve as the seeds of cloud droplet formation or ice crystal formation in clouds.  

Below is some data from the lidar ceilometer and microwave radiometer at Snowbasin from yesterday.  The lidar helps to identify cloud base and even snowfall below cloud base (top image).  The microwave radiometer provides profiles of the amount of supercooled liquid water in the cloud (bottom image).  In this case, the cloud was comprised of both ice crystals (some of which grew large enough to fall out as light snow at times) and supercooled liquid water droplets, with high concentrations up to about 3500 m MSL (11,000 ft).   

We have also positioned scanning Doppler on Wheels (DOW) radars on the Antelope Island Causeway and in east Huntsville to examine in fine detail the structure of storms across the Wasatch Range.  Compared to most weather radars you are probably familiar with, these radars are more sensitive, higher resolution, and can be programmed to scan vertically.  Below is a radar image from yesterday from the Huntsville site showing light precipitation in the Ogden and Morgan Valleys, areas where the National Weather Service Radar on Promontory Point is blocked by the northern Wasatch.  

We're super excited now to really dig into some storms, but Mother Nature is not being cooperative.  After today's snowshowers, the forecast is dry with a "death ridge" along the west coast for at least the next few days and in many ensemble forecasts beyond that.  So, I have both personal and professional reasons for hoping we get a needed pattern change.  

I hope to share some exciting observations at some point in the future.  

A Pretty Good Storm

Mother Nature brought the goods over the past two days.  Here are 48-hour water equivalents for the period ending at 11 AM 5 January:

Ben Lomond Peak Snotel: 2.8"
Snowbasin Boardwalk: 2.42"
Brighton Snotel: 2.6"
Alta-Collins: 3.73"
Snowbird Snotel: 4.0"

The trace of accumulated precipitation at Alta-Collins for the period snows that most of this fell in the past 24 hours.  In fact, the water-equivalent precipitation for the 24-hour period ending at 11 AM this morning was 3.03".  I'm always impressed by storms that produce 3" of water in 24 hours.  

Source: MesoWest

It's worth noting that this was a storm period characterized by southerly to southwesterly flow that shifted to westerly during the trough passage this morning.  Below is the wind speed (red line), gust (green plus signs), and wind direction (blue circles) on Mt. Baldy for the same period as above.  Note the predominance of southerly to southwesterly flow until around 0300 MST when the flow veered to westerly.  

Northwesterly flow gets a lot of attention, but southerly and southwesterly flow can bring the goods to Alta too, typically in the form of big water.  Snowfall amounts in these events are typically "subdued" due to the low snow-to-liquid ratios, as was the case in this storm.  Out of the 3.73" of water, the total snowfall was only 21", which represents a snow-to-liquid ratio of only 5.6 to 1 (a whopping 18% water content).  Although not the Greatest Snow on Earth, that's some of the Greatest Base Builder on Earth and just what we need.

The snow depth at Alta-Collins is now 64" and we have eclipsed 10" of water equivalent at the Atwater (13.5") and Snowbird (13.2") SNOTELs.  Thus, I am officially declaring the start of "good early season ski conditions)" since I often use 60" of snow or 10" of snowpack water equivalent for that threshold.  

This may be hard to believe, but as of last night the Snowbird and Brighton SNOTELs were at 95% and 93% of median snowpack water equivalent for the date, respectively.  Elsewhere things are worse, even much worse at lower elevations, but the upper elevations continue to claw their way to respectability.  

An Upward Trend

 Despite recent posts grumbling about warmth and a lack of snow at low elevations, the reality is that the skiing at upper elevations has been incrementally improving and all elevations should see gains in snowpack over the next several days.  

The upward trend began on Christmas Eve, which was likely the worst day of skiing I've ever had in the Wasatch.  Simply an abomination.  I've been out 3 days since, all at Alta, and each day things have improved.  Groomers today were just fine and we should be happy about that given where we were several days ago.  

And the forecast for the coming work week looks pretty good.  Mean Utah Snow Ensemble SWE for Alta Collins through 12Z 10 January (5 AM MST Saturday) is a around 3" and snow close to 40".  The driest ensemble member is about 1.5" of water an 17" of snow.  

More importantly, temperatures are falling.  Tomorrow remains unseasonably mild, but temperatures (and snow levels) decline gradually Sunday night and Monday.  During the day Monday, snow levels look to fall to near bench levels and remain near or below that level through the work week.  

Let's hope Mother Nature bings further improvement to ski and snowpack conditions.

Pity the Low Elevations

There's some healthy precipitation numbers in the Wasatch from this storm including as of about 11 AM this morning (Jan 2nd):

Sundance: 4.29"
Tibble Fork: 2.48"
Collins: 1.82"
Mill D North: 1.40"
Farmington SNOTEL: 2.2"
Snowbasin Boardwalk: 2.84"
Ben Lomond Peak SNOTEL: 3.50"

That's the good news.  The bad news is that snow levels have been high (reaching as high as 9000 feet late yesterday in the central Wasatch) so this is yet another storm period in which the lower elevations got skunked.  The base of Park City, for example, remains free of natural snow.  

Source: https://www.parkcitymountain.com/the-mountain/mountain-conditions/mountain-cams.aspx

Thoughts and prayers to the Wasatch Back.

At mid elevations, where there is snow, its DENSE and water logged.  At the Ben Lomond Peak SNOTEL (7600 feet), there's currently 8.2" of water packed into a snowpack that is only 22" deep.  That's a water content of 37% or a density of 370 kg/m3, as one might find in a maritime snowpack.  

Meanwhile, in the Salt Lake Valley, we finally cracked the smog or fog at around noon today.  Yesterday afternoon there were some great views of the valley fog from the Avenues.

Paraphrasing Albus Dumbledore, "pity the low elevations and, above all, those elevations without snow."

Good Riddance to 2025

Happy New Years from the Wasatch Weather Weenies.

2025 is now in the rearview and I'm not sad to see it go.  It was a tough year for science, higher eduction, the climate system, and at least for the start of the 2025/26 ski season, snow.

Let's begin with the Murderer's Row of climate statistics for Salt Lake City.

First, 2025 was the warmest year on record (since 1875) with an averge temperature of 57.9°F.

The last 3 months of the year and the first 3 months of the 2026 water year (Oct-Dec) were also the warmest on record, with an average temperature of 48.9°F.

And of course December was the warmest on record with an average temperature of 43.7°F.

Shifting gears to the mountains and focusing on the past three month, water-year-to-date precipitation (water equivalent) is actually not all that bad.  Many stations are within 90 to 109% of median (green) and those that are lower than that are withing 90 to 89% of median.  

As shown for Snowbird, a big contributor was the early October rains.  Those were followed by a long dry stretch in late October and November.  December precipitation though hasn't been all that bad.  

The problem, however, is warmth. The early October precipitation was mostly rain.  Even at upper elevations, it didn't add up to much.  Then the precipitation we have had this month has occurred with exceptional warmth for December.  Natural snow cover below 8000 feet is currently scant due to a significant fraction of December precipitation falling as rain instead of snow.  Even above 10000 feet you can find a rain crust in the central Wasatch from the post-Christmas storm.  Snowmaking conditions have been limited.

And today snow levels will eventually get to about 8500 feet. 

So, the story of 2025 in northern Utah was warmth, warmth, warmth.  Good riddance. Let's hope 2026 is better.