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

Just Past Peak Upper Elevation Snowpack

The statewide snowpack water equivalent, based on an average of all stations in Utah, peaked on April 1-2 at 18.8 inches and after fluctuating just below that value for about 10 days, has been steadily declining and now sits at 15 inches. 

Source: NRCS

The peak of 18.8 inches was 117.5% of the median peak of 16 inches, so it's been a decent snow year statewide.

The situation though varies depending on region and elevation.  We'll focus here on the Wasatch Range.  The lowest elevation SNOTEL site in the Wasatch is Ben Lomond Trail in the North Ogden Valley, which is at 5971 ft.  The snowpack at Ben Lomond Trail also peaked on April 1–2.  This is a snowy location, so the peak snowpack water equivalent was 28.4", more than 10" higher than the state average, despite the low elevation. 

Source: NRCS

After April 8, the snowmelt at this site began in earnest and it has since shed a bit more than 10" of water, or a bit over a third of the snowpack.  

Above this site at the Ben Lomond Peak SNOTEL site, which is at 7688 ft, the snowpack peaked at 53.4" where it sat at from April 8–11.  It has declined only slightly since.  

Source: NRCS

Here, energy from the sun and atmosphere in recent days have been warming the snowpack, but have not warmed the snowpack enough to produce much meltwater.  At this point, I suspect the snowpack at this location and elevation is close to "ripe" or near 0°C through its entire depth, so continued warm sunny days will likely yield a more rapid loss of snowpack.  

In the central Wasatch, the snowpack at the Parley's Summit SNOTEL at 7584 ft, however, is ripe and has been releasing meltwater.  Snowpack water equivalent has dropped from 19.2" on April 10 to 12.5" yesterday.  In a few days, the snowpack at this site will be about 50% of peak.  

Source: NRCS

The Snowbird SNOTEL at 9177 ft looks a lot like Ben Lomond Peak.  It maxed at 48.6" from April 8–13 and has declined just a smidge.  Here too energy from the sun and atmosphere have been warming the snowpack but have not warmed it enough to release meltwater.  Note that due to high elevation and a northern aspect, the median peak for snowpack at this site is actually in late April.  

Source: NRCS

Given that forecasts look pretty dry for at least the next few days and mild to warm, I suspect it is safe to say that we are well past peak snowpack now in the mid elevations, are probably past peak on upper elevation south aspects, and are likely past peak on upper elevation north aspects.  

It's a shame we can't save about half of this snow for next season.  

The Fate of Alpine Glaciers

In the previous post, Climate Change Case Study: Austria, we examined recent trends in snow measures and potential impacts of future warming on skiing in the eastern Alps.  Declines in snow and snowcover are evident in the recent past and expected to continue in the next few decades in low- and mid-elevation areas.  High-elevation resorts in Tyrol, where resorts more commonly extend above 2000 meters, are the most "climate resilient" but will still feel the effects of climate change.  Ski area viability declines with ongoing greenhouse gas emissions and future warming.  One estimate suggest that with 2°C of warming relative to 1961–1990, only 64% of Austrian ski areas will be snow reliable.  With 4°C of warming, this number drops to 16%.  

In this post we look at the fate of glaciers in the Alps.  Glaciers are large masses of land-based, perennial ice, and they exist at upper-elevations throughout the Alps.  The map below shows the Alpine glacier coverage circa 2010.  Small glaciers are found from the far western to far eastern Alps, with the greatest concentration of large (5–100 square km) glaciers in the highest Alpine terrain from roughly Mt. Blanc to Zermatt (between about 6.75°E and 8°E).

Source: Huss (2012)

Large glaciers exist elsewhere in the Alps, however, including the Swiss Jungfrau (southeast of Bern), where the Aletsch Glacier glacier, the largest and longest in the Alps is found, the Ötztal and Stubai Alps of Austria's Tyrol, the Ortler and Rhaetian Alps of Italy southwest of Bolzano, and the Hohe Tauern in eastern Austria (between 12°E and 13°E).  

Monte Rosa and the Gorner Glacier above Zermatt

Glaciers in the Alps have been losing mass and retreating in recent decades.  This reflects what is happening across the globe.  The graph below shows the cumulative mass change in mass balance for reference (i.e., well-monitored over decades) glaciers (in cumulative meters of water equivalent) illustrating the downward trend.  Central Europe (blue) includes trends from Austrian (6), Swiss (5), French (3), Italian (2), and Spanish (1, Pyrenees) glaciers. 

It is not unusual for people to argue that these trends in the Alps are due to emergence from the Little Ice Age However, since 1990, a majority of the glacier loss, which is accelerating, is due to human-caused climate change. 

A sad reality for Alpine glaciers is that if we could stop global warming right now, they would probably still lose a substantial amount of volume.  Zekollari et al. (2019), estimated that if the 1988–2017 climate predominated through the 21st century, almost 40% of the glacier mass in the Alps would be lost.  They referred to this as committed loss.  

Source: Zekollari et al. (2019), with annotations added.

This is because the Alpine glaciers are currently out of equilibrium with the rapid warming that has occurred in recent decades.  Given time, even in a stationary climate, they will continue to retreat and shrink.  Not surprisingly, mass losses increase with emissions and warming.  In moderate and high emissions scenarios in which global temperatures increase by 2–4°C, more than 70% of the glacier mass of the Alps is gone.  In the csae of the latter, the only glacier remnants remaining in the Alps are in the high terrain from Mt. Blanc to Zermatt and the Swiss Jungfrau.

Source: Zekollari et al. (2019), with annotations added.

Last week, the Austrian Alpine Club released it's annual glacier survey and report.  They have been surveying glaciers in Austria for over 100 years, but this one got a lot of coverage because they warned that Austria will be largely ice free in 45 years.  In other words, perennial ice will largely be gone.  This is generally consistent with my scientific understanding, although I hope that perhaps some high-altitude glacier remnants may survive in the Austrian Alps if we can get our act together. 

Climate Change Case Study: Austria

It was a great ski season here in northern Utah, but the situation at low elevations in the Alps this year was dismal.  The photo below was taken on March 3rd at Brixen im Thale, part of the SkiWelt Wilderkaiser – Brixental megaresort in the eastern Tyrol of Austria.  Despite it being early March, the natural snowpack was non-existent and artificial snow was scant.  

This is a low elevation area.  The photo is taken at 800 meters and much of the skiing in this region is is below 2000 meters.  At these elevations, snow is especially vulnerable to temperature, and this winter was remarkably warm in the Austrian Alps.  Geosphere Austria, the state meteorological and geophysical science service, reported that February was the warmest on record, with a mean temperature in mountainous areas an incredible 5.9°C (10.6°F) above the 1961–1990 average. The impacts can be seen above.  This was followed by a March that rated as the warmest in history in the Austrian lowlands and the ninth warmest in the mountains.  Basically, this winter was a disaster for lower-elevation skiing.  

On the other hand, March snow depths at upper elevations of the western Austria states of Vorarlberg and Tyrol were 10 to 20 percent above average, whereas in the central Austrian States they were near average.  Basically, it was a tale of two altitudes.  That said, does this represent the future of skiing in the Austrian Alps?  Let's take a look.

Recent Trends

Austria has an extensive snowpack observing system.  For the 2nd edition of Secrets of the Greatest Snow on Earth, Marc Olefs of Geosphere provided me with long-term trends of seasonal mean snow depth (top figure below) and snow cover duration (bottom figure below) in Austria from 1961–2021.  No observing sites in Austria show positive trends in either of these variables. Roughly 67% exhibit statistically significant declines in average snow depth and 80% show statistically significant declines in snow-cover duration (i.e., the length of time with at least 1 cm of snow on the ground).  These trends tend to be largest at lower elevations.

Source: Steenburgh (2023).  Data from Olefs et al. 2021 and updated through 2021.

Note that with one exception, these sites are below 2000 meters.  In western Austria, there are resorts that go to well above that elevation, including a few places where lifts extend to more than 3000 meters, such as Stubai Glacier, Hintertux Glacier, and Sölden.  These resorts have upper-elevation glacier skiing and typically long seasons.  Hintertux Glacier is currently the only ski area in the world with year-round operations (Zermatt attempts to do this, but has not been able to the past two years due to poor glacier conditions).  

It is well documented that glaciers in the Alps are loosing remarkable amounts of mass.  One of the most studied glaciers in the world is the Hintereisferner in the Ötztal Alps about 15 to 20 km from Sölden as the crow flies.  The annual mass balance of the Hintereisferner has been negative every year since 1983 and losses have been accelerating.  

Source: https://wgms.ch/products_ref_glaciers/hintereisferner-alps/

There are no "good" years for glaciers in the Alps anymore.  Oh, you might hear that they had a good winter (this winter might have been a decent one at upper elevations), but the insidious influence of temperature is simply too overwhelming.  Hintertux Glacier goes to extreme lengths to enable summer skiing operations, which I suspect are not going to continue much longer.  

Source: Steenburgh (2023), from 80-20/Shuterstock.com

Future Snowfall Trends

I often tell people that global warming is not an equal opportunity offender.  The snow climate of the Alps will suffer at all elevations, but the percentage declines in snowfall and snowpack will be largest at low elevations and smallest at upper elevations.  Let's have a look at some projections. 

In 2018, Prisco Frei and coauthors from ETH Zurich and MeteoSwiss used regional climate modeling to estimate trends in September to May snowfall across the Alps relative to 1981–2010. Their paper (Frei et al. 2018) is one of the best deep dives into future snowpack trends in the Alps, but very useful for understanding what may happen in other regions.  They used multiple simulations from regional climate models to do this.  

For brevity, I will show one figure showing estimated trends in mean September to May snowfall from 1981–2010 to 2070–2099 under a moderate emissions scenario (known as RCP4.5) in which climate models produce an average warming of global mean temperatures of about 2˚C during the 21st century [Ed: this was corrected from 20th century in the original version of this post] and a high emissions scenario (RCP8.5) that produces almost 4˚C of warming (warming in the Alps would be greater that the global average temperature increase).  The slide below summarizes the estimated trends with the medians in each elevation band indicated by triangles and the range produced by the models by the color-filled area.  For both scenarios, declines are largest at lower elevations and decrease with elevation.  For the 1000–1250 m elevation band, the snowfall declines are 15–40% under the moderate emissions scenario, but at 2250–2500 m, they are 1–18%. 

Source: Frei et al. (2018)

The primary cause of these declines is a greater fraction of precipitation falling as rain instead of snow.  Note that the declines increase with higher emissions and greater warming.  The decisions we make today and in the immediate future do matter and do make a difference. 

Impacts on Skiing

How will this affect skiing and ski area operations?  This is a critical question for Austria because winter tourism generates about 6% of their GDP through direct and indirect effects.   Despite having a population of under 9 million people, Austria is 2nd in the world (to the United States) with over 40 million skier days per year at ski resorts.  Roughly 66% of these skiers are foreign tourists.  For comparison, Utah had a record breaking 7.1 million skier days last year.  

In 2011, Robert Steiger and Bruno Abegg of the University of Innsbruck examined the natural snow reliability of 228 Austrian ski areas.  They defined snow reliable as having at least 100 days with at least 30 cm of natural snow in 7 out of 10 winters at the midpoint of the ski area.  This is a simplistic approach, but we will use it here to illustrate some regional and topographic differences in ski resort vulnerability.  They also used some simple modeling to assess reliability with snowmaking.  

Results for the 228 Austrian Ski Areas are presented below.  I have added some annotations.  Their baseline period was 1961–1990.  During that period 97% of Austrian ski areas were snow reliable with snowmaking.  80% were snow reliable with natural snow.  As temperatures increase above what was observed during that 30 year period, the number of snow reliable ski areas declines.  For 2°C of warming, only 40% of Austrian Ski Areas are naturally snow reliable and only 64% are reliable with snowmaking.  

Source: Steiger and Abegg (2011)

They also broke these estimates down by region.  The figure below shows versions of the graph above for each Austrian State with the baseline being the left-most bar and 4°C of warming being the right-most bar. I've used an arrow to indicate the 2°C of warming estimate. 

Source: Steiger and Abegg

In Lower Austria, where most resorts are at lower elevations, no ski resorts are naturally snow reliable with 2°C of warming and only 1 is snow reliable with snowmaking.  That contrasts with all 13 being naturally snow reliable from 1961–1990.  In contrast, higher-elevation regions with higher elevation ski areas are more resilient to warming.  This is especially evident in Tyrol and Salzburg where a greater fraction of resorts are naturally snow reliable or reliable with snowmaking than in Lower Austria, Upper Austria, and Styria where resorts are lower.

This doesn't mean that resorts in Tyrol and Salzburg are unaffected by warming.  We began this long post with a photo of Brixen im Thale in eastern Tyrol showing a disastrous situation for skiing.  Resorts with high-elevation terrain but large vertical drops will see more rapid declines in snow reliability at low elevations than at upper elevations.  For instance, a resort like Sölden, which has more than 6000 feet of lift-served vertical, may be more snow reliable at upper elevations, but find low elevations increasingly unreliable. The photos below were taken on the same day in March. 

Many villages in the Alps are in deeply incised valleys and at low elevations.  Snowmaking is already essential, but will become increasingly so in the future.  At some resorts, new lifts may be needed to increase the capacity for up and downloading to and from areas that are more snow sure. 

Summary

We are now in the early stages of what Brian Fagan called The Great Warming.  The snow climate of the 20th century is gone forever.  Some regions are more vulnerable to the initial wave of global warming than others and lower elevations of the Austrian Alps is one of those regions.  There are other great snow climates that are also highly vulnerable, including low-elevations of Japan's heavy snow region near the Sea of Japan where historically most of the snow fell at temperatures near or even a bit above 0°C.  A small amount of warming in those areas is the difference between rain and snow.  

Skiing in some low-elevation regions of the Austrian Alps may already be doomed.  That said, there is still time to save skiing in upper-elevations of the Austrian Alps.  If we were to contain global warming, skiing will survive in those areas, albeit with some major changes, such as a major decline in lift-served ski terrain with glaciers, more rain-on-snow events, and a shorter snow-cover duration season. 

It's Over

I'm calling it. Spring is here.  Powder skiing chances now will be increasing intermittent. 

The final powder weekend was a good one.  It was ideal for April powder skiing with a goldilocks dump that covered much of the buried crusts, a remarkably cold airmass, and enough cloud cover to limit the caustic effects of the now high-angle sun.  

Forecasts for this week are not hopeful if you are hoping powder.  Below is the 7-day GFS.  Mt. Baldy (11,000 ft) tempeatures rising the next few days into the 30s.  Near 50 at Alta Collins.  Maybe a shower or two, but not enough to enable real powder skiing.  

At some point a cold trough will push in here and we'll see snow again. This is after all spring in Utah.  You might even get another deep powder day or two in.  It happens.  But for all intents and purposes, it's over.  Hope you enjoyed it.  All in all a pretty good season.  Enjoy the corn.  

Alta 600

Alta went over the coveted 600 inch mark today thanks to ongoing showshowers that for a time in the morning featured a bonafide mid-lake band.  It has been a long time since I can remember a solitary, well-developed mid-lake bands taking aim at the Cottonwoods.  The image below is for 1329 UTC (7:29 AM MDT). 

Rumors are it was a hell of a day of skiing.  Good for you if you were up and enjoying the early April freshies.  

It's still stacking up as I write this at a bit after 5 PM.  Total snow depth is now up to 181", or a bit over 4.5 meters for the rest of the world.  

Some more snow showers through tomorrow.  My thinking is a few more inches for Alta, mainly this evening, but Mother Nature seems like she wants to keep it coming these days so who knows.  Tomorrow the sun could make some appearances, which might complicate matters for powder preservation, although it is a pretty cold airmass, which will help on some aspects and at upper elevations.  I liked this quote from today's Utah Avalanche Center forecast:

"Will the new snow be stable or unstable? I do not know. Therefore, you have to be your own avalanche forecaster."

I'll use that for inspiration.  Watch the radar and be your own weather forecaster.  

Winter Returns Again

Our spring roller coaster ride continues this week.  Yesterday we cracked 70˚F for the first time this calendar year at the Salt Lake City International Airport.  It also hit 50˚F at Alta-Collins (9662 ft).  Today we will add high clouds and wind to the mix, but will remain mild.

The weekend though will be colder.  Much colder.  The change happens on Friday with the arrival of a deep closed low and cold front. The latter looks to sweep across Utah during the day, putting is in cold, southwesterly flow tomorrow afternoon.  You read that right: cold, southwesterly flow.  This is a trough that digs southward along the California coast, bringing cold air with it.  As a result, as seen in the GFS forecast below, the cold air initially moves into Utah with southerly and southwesterly flow at 700-mb (crest level) tomorrow.  

It takes a while, but we eventually see cold westerly and northwesterly flow once the trough has moved downstream late Saturday.

For Alta-Collins, the GFS has two major periods of precipitation, one during the day tomorrow roughly with the frontal passage, and then during the day Saturday and Saturday night with and in the wake of the upper-level trough.  There are a few dribs and drabs between those two storm periods.

Overall, the GFS generates 1.3" of water and 21" of snow for Alta-Collins.  I took a quick look a the Euro and the downscaled SREF and the GFS is on the wet side of the model runs.  The downscaled SREF mean is around 0.75" of water and 13" of snow.  

I suspect this will be a situation where patience is a virtue.  It will take time to bury the frozen coral reef that will setup tonight and tomorrow.  If things come in heavy tomorrow, perhaps Saturday morning will ski well, but more likely it will take some time to bury things.  Hopefully we end up with a GFS-like solution with over an inch of water and something close to 20" by Sunday.  My best guess is 12-24" for Alta-Collins. 

Winter Continues

It's a great pattern for late March with snowfall continuing today.  Overnight, Alta-Collins picked up 6 inches (as of 7 am) and the radar looks pretty filled in as I write this at 7:20 AM.

Snow today from 7 AM to 5 PM should add another 3-6" to the stake.  The HRRR says morning will be more active than afternoon, whereas the GFS keeps it going for most of the day.  Let's hope the latter verifies as that might push us above my forecast range.  

Periods of snow will continue through Sunday night, with perhaps some snow showers on Monday.  I'm not sure if it will stay cloudy and snowy enough on Monday to help preserve the snow, or if we will start to see the caustic effects of the sun.  After Monday though, warmth and sun return this great powder run will come to an end.

The Goods on Graupel

Ski conditions in the Wasatch backcountry continue to be excellent with cold weather and cloudy skies enabling pretty good snow preservation despite it being late March.

Over the past couple of days, a lot of the snow that has fallen has been in the form of graupel, which is an opaque, white snow pellet that sometimes takes a lump, hexagonal, or conical form. Graupel often causes the snow surface to have a dippin' dots appearance.  

Catch some on your sleeve and take a close look you'll find that graupel particles are aggregates of a bazillion tiny frozen cloud droplets.  

Graupel forms in strong updrafts when supercooled cloud droplets freeze on falling snowflakes.  Supercooled means that the cloud droplets are unfrozen, despite being colder than 0˚C.  These droplets freeze on contact.  This process is sometimes called riming or accretion.  If the riming is light, you can still distinguish the original snowflake.  However, at the extreme, the flake is completely coated and you get graupel.  

One of the reasons why we have had so much graupel the past few days is that it's been very unstable.  Graupel requires strong updrafts to suspect a snow crystal until it is fully rimed.  Snowflakes typically have a fall speed of about 1 meter per second.  Graupel is about 3 meters per second.  So, if you want big graupel, you typically need updrafts of at least 3 meters per second.  

Graupel is important for thunderstorm electrification.  In thunderstorm updrafts, smaller ice crystals are often carried upward by updrafts, whereas the larger graupel particles can fall out.  This contributes to the charge separation process within the cloud and in some cases lightning and thunder.  This happens even in summer thunderstorms, which extend well above the freezing level, although in those small hail can also form and be a contributor to electrification).  This has been happening some in Utah the past couple of days.  Snowbasin closed early yesterday due to lightning.  

People are often surprised by thundersnow, but the process is the same as in summer thunderstorms. It's just less common because you need strong updrafts and those are less common in many winter storms. Lake effect snowbelts see thundersnow more frequently because lake-effect storms often have strong updrafts.  In northern Utah, the daytime heating if post-frontal cold airmasses in the spring can also lead to strong updrafts and thundersnow.  

Because graupel is dense and has a higher fall speed, it can penetrate farther below the melting level than most snowflakes.  Thus, sometimes you see graupel falling at higher temperatures than snowflakes.  

Graupel should not be confused with sleet.  Sleet is a translucent ice pellet.  Unlike graupel, which is opaque and typically a bit pliable if you squeeze it, sleet is hard.  Sleet also forms through a different pathway.  Sleet forms when snow falls into a warm layer aloft with temperatures above 0˚C and melts into rain or droplets that are predominantly water with perhaps a small particle of ice in it.  It then falls into a colder layer near the surface that is below 0˚C and freezes.  

Sleet is basically a frozen raindrop.  Graupel is a snow particle formed by riming.  Very different processes.  Graupel skis much better than sleet.  You would definitely notice the difference.  Sleet is exceptionally rare in northern Utah (I'm not sure if I've ever seen it here). 

Enjoy the graupel skiing while it lasts. 

Just What the Doctor Ordered

The Saturday night frontal passage seemed to provide just what the doctor ordered for transitioning from spring skiing back to proper powder skiing.  I found good skiing yesterday with just a hint of bottom feeding at mid elevations if you kept the slope angles reasonable.  

Storm totals per the Alta-Collins site are now over two feet.  Elsewhere, a healthy lake band developed overnight, but raged over the western Salt Lake and Utah Valleys.  

It has since broken up some but scattered lake-effect snowshowers continue this morning, albeit a bit farther west than central Wasatch skiers would like. 

The unsettled post-frontal weather will continue through Tuesday evening.  Although not in the lake-effect now, expect periods of snow showers throughout this period in the Cottonwoods and perhaps even a thunderstorm or two in the afternoons.  For the period from 6 AM MDT this morning through 6 PM 12 AM MDT Wednesday March 27, the GFS produces .79" of water and 14.7" of snow at Alta.  The HRRR was less excited (.44"/7.6").  Regardless, it will come in fits and starts, which is my new phrase for the week.  It's great skiing for late March.  Hopefully the sun will not do too much damage when it appears at times.  

Enjoy.

Storm Update

Pretty good delivery of the white in the upper Cottonwoods yesterday afternoon and last night. As of 6 AM, Alta-Collins is already at 13 inches with 1.32" of water.  That's a mean water content of 10%, although I suspect it's right side up.  We need some high density snow to bury the coral reef anyway.  All in all this is good news.  

Radar early this morning showed a fairly active northwesterly flow pattern.    

Expect periods of snow in the northwesterly flow to continue today.  The HRRR really lights it up with .66" of water and 11.1" of snow at Alta from 7 AM to 5 PM MDT today.  The GFS is not as excited puts out .19" of water and 3.6" of snow.  A big reason for this discrepancy is the HRRR really gets things going in the northwesterly flow, including some lake effect, as illustrated by the forecast radar image for 2000 UTC (2 PM) this afternoon.  

And for the 6-h period ending at 0000 UTC (6 PM MDT) the HRRR is generating 7.5" of snow for Alta and even higher amounts along the Alpine ridge to the west in the Lone Peak area.  

A real question is how much to buy into the HRRR forecast?  I'm inclined to expect another 4-8" at Alta-Collins for 7 AM this morning through 5 PM this afternoon, which sits between the GFS and HRRR.  I'd put the odds of going above that higher than below.  How bout we throw in the chance of a T-storm too?  Welcome to spring.

Winter to Return

After about a week of splendid spring weather, winter will be returning to the Wasatch Range today with the arrival of a cold front this evening.  

Although there will be some periods of high-elevation snow and low elevation rain ahead of the front, the main action will be associated with the frontal passage which will bring a few hours of steady snowfall overnight.  

The cold-front is very apparent in the latest HRRR run with an abrupt drop in the wet-bulb zero height at between 7 and 8 PM.  

We base the wet-bulb zero level estimate on the model forecast from the airport (if we used data from Alta we would not be able to estimate snow level most of the winter since there's no data below ground), so expect that drop to be more like from 8-9 PM in Little Cottonwood.  Snow levels are usually a bit below the wet-bulb zero, so expect them to be in the area of 7000-7500 feet today, possibly higher in the afternoon with heating, and then drop to near bench levels after the frontal passage.  

The HRRR is calling for about 0.85" of water and 8.6" of snow at Alta Collins through 9 AM Sunday.  A bit less than half of this is high density snow that falls in fits and starts ahead of the front, including this afternoon, and the remainder is with the frontal passage.  Densities will be decreasing behind the front.  

The HRRR then shuts things down late tonight through tomorrow afternoon when things begin to pick up again.

The GFS is less enthused about the pre-frontal precipitation today but is in rough agreement on the frontal passage.  It's also a bit more active during the day tomorrow.  Through 9 AM Sunday it's at .55" of water and 7.6" of snow.  

So, expect some fits and starts of wet snow at upper elevations today and then steady snow with the frontal passage this evening and tonight.  I'm inclined to go close to the model water numbers on this with 0.5 to 1" of water and 6-10 inches of snow at upper elevations through 9 AM tomorrow.  

Given the warmth of the past week, I'm not overly optimistic that the frozen coral reef will be buried by tomorrow morning.  Things will need to go above those numbers probably to prevent a lot of bottom feeding.  If that doesn't happen, the better skiing tomorrow morning will probably be in lower angle terrain where the snow surface is currently fairly smooth.

That said, behind the front, unstable northwesterly flow looks to predominate through at least Tuesday and possibly Tuesday night.  The GFS time-height section shows this well.

Thus, expect more periods of snow Sunday through Tuesday, with the coral reef becoming more and more submerged and a return to more winter-like ski conditions in the upper Cottonwoods.

Beautiful Spring Weather

If you look carefully, you can see a couple of clouds in the Mt. Baldy web cam from Alta Ski Area this morning.

Source: Alta Ski Area

Those are not enough, however, to mar the incredible run of beautiful weather we have had since the demise of the easterlies on Saturday.  

Indeed, that run will continue today with clear skies and temperatures into the upper 60s in the valley.  If we can't have powder, this is a pretty good alternative.  

A weak short-wave trough will come through tomorrow and bring in a few more clouds and maybe a spritz of a shower or upper-elevation snow shower for the mountains tomorrow.  Significant weather will hold off until the weekend when a cold front is expected to push across northern Utah on Saturday.  Current forecasts suggest that the front will arrive in the afternoon.  Below is the ECMWF forecast valid 2100 UTC 23 March (3 PM MDT Saturday) with the front approaching Salt Lake City.

A real question mark for skiing will be whether or not that storm produces enough snow to bury the coral reef from the warm sunny weather this week.  We shall see.

I used the ECMWF above because I just upgraded the graphics produced for it on weather.utah.edu.  While I was in Austria, ECMWF opened up more of their data for free access.  We are now getting higher resolution data (0.25 degrees instead of 0.4 degrees), radiation fields that allow me to put together a synthetic cloud image (see upper right), vertical velocity (see upper left...smoothed to show the large-scale vertical motion), and additional wind and humidity information that allows me to better calculate integrated vapor transport (lower right).  

Sastrugi

Along with graupel, sastrugi is one of my favorite weather-related words and I saw plenty of it ski touring yesterday.  

Sastrugi is defined by avalanche.org as "heavily wind eroded snow with wavy textures." Sometimes it looks rough or pockety.  In the photo below, it appears there is avalanche debris on this slope, but in reality it is all sastrugi.  

In some areas, the sastrugi was dense wind board and generally supportive of a skier. 

In others, it was actually somewhat soft and didn't ski to bad on the descent. Each turn was a mystery!

Although I like sastrugi as a word, it's not my favorite snow surface to ski.  We can blame the sastrugi in this case on the multiday easterly wind event that has been affecting the Wasatch Range and Front since Thursday.  Observations from Alta's Mt. Baldy show the winds veering (turning clockwise) from southwesterly just prior to 1200 MCT 12 March (Tuesday) to north by 0000 MDT 14 March and then locking in with easterly flow with gusts reaching over 50 mph on the 15th (Friday) when most of the damage was done. 

The large-scale setup for these winds was something that meteorologists call anticyclonic wave breaking in which a high-amplitude ridge develops in the high latitudes and leads to the formation of a closed low downstream and to the south.  Below is the GFS analysis for 1200 UTC 15 March during the period of stronger easterly flow on Mt. Baldy.  Note the ridge off the Pacific Northwest coast and the deep closed low centered along the CA-MX border, resulting in strong easterly 700-mb (crest-level) flow over the Wasatch. 

This is the same pattern that produced heavy snowfall along the Colorado Front Range. Basically, this is a complete reversal of the climatological westerlies.  They get upslope and we get downslope.  

The pattern has been very persistent and this morning enhanced easterlies ares still being observed along the east bench of the Salt Lake Valley north of Holladay, although they are weaker than at the peak.