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. 

Saturday, March 30, 2024

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.

Wednesday, March 27, 2024

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.