Friday, April 19, 2024

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.  

Tuesday, April 16, 2024

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. 

Wednesday, April 10, 2024

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. 

Tuesday, April 9, 2024

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.  

Saturday, April 6, 2024

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.  

Thursday, April 4, 2024

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.