Classic "Nord Stau" Storm

We have finally gotten a taste of winter here in Innsbruck with a storm that has lasted for a bit over 36 hours in the mountains and has provided a steady snowfall even on the Inn Valley floor.  I had a beautiful walk to the office this morning following the walking path from our flat above town and then across the Inn River.  

Explosions from avalanche mitigation work on the Nordkette ridge above town are shaking the windows of my office currently.  Skies are still overcast, so I can't see the results.  I've been here when you can watch the avalanches from town.  

The snow was produced by a cold-frontal passage Wednesday evening followed by a period of northerly post-frontal flow, or what is sometimes referred to as "Nord Stau" in which northerly flow impinges on the Alps and experiences blocking and orographic lift.  This is the eastern Alps equivalent of northwesterly flow in the Cottonwoods, although the snowfall is much more expansive in area.  Below is the ECMWF HRES analysis for 0000 UTC Thursday 26 March during the Nord Stau period of the storm showing a deep upper-level trough over Germany, Switzerland, and Austria at 500 mb (hence cold and unstable) with moist north-northwesterly flow impinging on the Alps at 700 mb.  

The European radar composite from 1630 UTC late yesterday afternoon was a classic with convective cells upstrea of the Alps over Germany and France.  These were moving south-southeastward toward the Alps where the convection became more continuous over then northern Alpine Rim of Switzerland, German, and Austria.  Note the lack of echoes over Italy, which was in the lee of the Alps.   This is all happening in the wake of a low-level cyclone (i.e., low pressure system) that was producing broader, stratiform precipitation over eastern Europe.  

The "Euroregion" comprised of the Austrian state of Tirol and Italian states of South Tyrol and Trentino collaborate extensively on snow measurements and avalanche warnings.  There is a dense array of automated snow depth sensors in this Euroregion operated by many groups.  These measure total depth and one can access the 48-hour difference in snow height from these sites athttps://avalanche.report/weather/stations.  While not strictly equivalent to new snow amounts, in this case they provide a reasonable estimate of snowfall amounts given the well-consolidated snowpack before the start of this case. 

As is typically the case in Nord Stau, snowfall from this storm was greatest in what is known as the Northern Alpine Rim, which in western Austria is north of the Inn Valley and includes the snowy region near and around the Arlberg Pass (simply called the Arlberg).  There are a number of stations with 48-hour increases in snow height over 50 cm (20 inches).    

48-hour difference in snow height for the period ending ~0730 UTC 27 March. Source: https://avalanche.report/weather/stations. 

Snowfall decreases as one moves southward into the Inner Alps of Tyrol.  For example, in the Alps around the Paznaun valley, snowfall amounts are genreally less than 45 cm and in some areas less than 20 cm.  One area of the Inner Alps with greater snowfall is in the Tux Alps just west of the Ziller Valley, which I've circled in the right of the diagram.  Not shown here are areas farther east in the Kitzbuhel, Zell am See, and Hohen Tauern that also saw more than 50 cm where storm penetration into the inner Alps is often a bit stronger than in the Innsbruck area.  

The Austrian-Italian border (and farther west the Swiss-Italian border) represents the Main Divide of the Alps, which is the hydrologic divide.  Although the highest peaks near the Main Divide are quite high, snowfall is more limited.  There are a couple of sites just north of the main divide with > 30 cm but many other sites have lesser precipitation.  This is not uncommon as Nord Stau storms tend to dump their loads on the Northern Alpine Rim with less snowfall over the Inner Alps.  

Once south of the Main Divide, snowfall decreases further into the lee and South Tyrol.  There are some light amounts in the Dolomites, but those were actually produced during the passage of the cyclone rather than in the post-frontal Nord Stau period.  In situations like this, you have your pick of powder on the northern Alpine rim or dry weather for hiking or biking in South Tyrol.  Just take the regional train from Brenner Pass on the Alpine Rim until you find the weather that you want.  

During this an many other storms, there can be a good deal of variability in the change in snow depth in any Alpine region.  In part, this reflects they large contrasts in the elevations of stations, but also the fact that there is a good deal of snow redistribution by the wind above timberline in the Alps, both prior to deposition on the ground and after.  I'm still trying to learn what sites are generally representative of the immediate surrounding area.  

The good news here is that after a break later today and tomorrow (Saturday), there's another storm coming in.  Unlike what has happened in Utah, this should enable many resorts to make it to their target closing dates.  

Heat Wave Numbers

It is snowing today (Thursday) in Innsbruck, the first valley snow since we arrived in late February.  It's just above freezing so that the snow is sticking on cold surfaces, but sidewalks and roads are snow free.  Below is the view from my office. 

I haven't thought about the weather in Utah in a few days.  I knew it was going to be hot, but now that I'm checking the numbers, I'm pretty blown away.  Multiple days at or above 80, including an 84(!) on   Saturday March 21. 

Let's put those numbers into historical context.  During the 20th century, the highest March temperature recorded at the Salt Lake City International Airport was 78°F, reached on 24 March 1956 and 26 March 1960.  During the 21st century, we have tied or topped that number 14 times.  This includes reaching 80°F for the first time on 31 March 2012 and reaching or exceeding 80°F five times in the current heat wave, including the mind-boggling 84°F.

Let's dig a little deeper.  For the 8-day period ending yesterday (Wednesday, March 25), the average maximum temperature was 78.3°F.  The previous March record for an 8-day period was 74.4°F set in 2017.  The 20th century record, 70.0°F, was set in 1960.  So, the average maximum temperature for this stretch is an astounding 8.3°F higher than anything observed in March during the 20th century.  

How about average temperature?  For the 8-day period ending yesterday (Wednesday, March 25), the average temperature was 64.2°F.  The previous March record was 61.6°F set in 2017.  The 20th century record, 57.8°F, was set in 1910.  Thus, for average temperature the current 8-day stretch is 6.4°F warmer than anything observed in March during the 20th century.  

I just pulled up the Alta website and noticed they are closing Wildcat and Collins Gulch early due to unseasonable warmth.

Source:Alta.com

We are deep in uncharted territory.  There is no historical analog for the current March heat wave.  Nothing is even close.    

You Were Warned

Mind boggling temperatures from the western United States currently.  Even watching from a distance here in Austria, they blow me away. 

As I write this, it is Friday morning in Austria and some of the numbers for Thursday in the US are not in yet.  Thus I'm going to use observations from Wednesday to illustrate the scale and intensity of this event before boring into what data I have access to from Thursday.  

Below are the rankings for high temperatures on Wednesday relative to prior March 18ths.  Wide spread records for the date across the southwest US but even all the way up into Montana (asterisks indicate a tie for the highest temperature of the date).  It appears every western state had at least one station that tied or set a record temperature for the date.  Washington was the "coolest" western state, but even there, Chelan tied their record high.   

Source: https://sercc.oasis.unc.edu/Map.php

Departures from average were impressively high.  Many sites were more than 20°F above average, and this is likely the 1991-2020 average so departure relative to the now old and obsolete 20th century average would be even bigger.  Some sites were at or above 25°F above average.  I couldn't find a +30, but maybe it's in there somewhere.    

Source: https://sercc.oasis.unc.edu/Map.php

Wednesday's highest temperature was 108°F at a location near North Shore, CA, which is not on the Pacific Ocean but instead the Salton Sea.  Yesterday (Thursday), Palm Springs hit 107, Thermal 108, and Indio 108.  I believe those 108s are all time monthly maximum temperature records for March and possibly all time for the entire US.  Adding to the misery a bit further east is 106 in Yuma and 105 in Phoenix.  

Records in the Palm Springs Area go back to 1922.  In 1938 they hit 100 in March for the first time.  In 1966 104.  In 1988 103. And now this year 106 (Wednesday) and 107 (Thursday).  In Thermal, records go back to 1951.  They hit 102 in 1966 and 1988 and now 107.  

Meanwhile in Salt Lake City, yesterdays 79 was a record for the date but not the month.  The monthly record is still 80, set on 31 March 2012.  Don't worry.  We'll likely set a new record on Friday and/or Saturday.  

Utah ski areas are suffering.  Eagle Point and Cherry Peak are closed.  Snowbasin's last day is Sunday.  That's a major Utah ski resort, ranked #1 in the US by some surveys and rankings, with a substantive snowmaking system, packing it in on March 22nd.  I looked at the webcam from the base of Wildcat yesterday and I simply could not believe it. It doesn't even seem possible.  

https://www.snowbasin.com/the-mountain/web-cams/

My heart goes out to the resort, which moved heaven and Earth for us this winter for our field campaign.  Despite a slow start to the season, we actually got some great data and will learn a lot, but never in my wildest dreams did I expect to see such a sparse natural snowpack in mid March.  

Here are a few SNOTEL observations based on data from Wednesday, the most recent data that I have available as I write this. There is no snow at Ben Lomond Trail. Median for March 18 is 17.6".  The snowpack at Ben Lomond Peak (7690 ft) appears to be ripe (i.e., it has warmed through depth to 0ºC) and has declined 3.3 inches from its peak and sits just above it's all time low for the date.  Snowbird is not at an all-time low, but it also appears to have declined some from its peak, although that site is a little flaky so I'm not going to fully endorse that as reality (maybe someone can comment).  That said, all other SNOTEL sites in the central Wasatch have seen declines in total snowpack water equivalent in the past few days.  Not necessarily a lot, but some.  

My view of these events is that they are not the new normal, but they are the new extreme, at least for now.  We should expect natural climate variability to still give our winters and snowpacks ups and downs in the coming years, including some good or even great snow years (as we just had in 2022/23).  But, we are seeing an emerging trend to warmer conditions, meaning more frequent, more intense, and longer duration heat waves, more precipitation falling as rain instead of snow, more mid-winter snowmelt events, etc.  These trends, caused by human-caused global warming, will have the biggest impact on snowfall and snowpack in the lower elevations, as we have seen this season, but will also bring change to the upper elevations.  

The reality is that you were warned.  Some of you took it seriously.  Others have called it a hoax and even today are working to dismantle the outstanding US climate-science enterprise, such as breaking up world-class research institutes like the National Center for Atmospheric Research (NCAR).  Still others are pushing fossil fuels and delaying a transition to a lower-carbon world.  

Due to the slow response of the climate system and socio-economic change, we are already committed to more warming in the next 20-30 years (maybe longer).  Will the powers that be continue to resist change and pursue a high carbon, fossil fueled future?  Good luck with that.  

My "Run of Fame"

Call it a guilty pleasure given the industrial-scale nature of the resort development, but I absolutely love skiing from valley to valley and village to village in the Arlberg region of western Austria where lift-served skiing extends from St. Anton to the south to Warth to the north, a distance of 16 km as the crow flies and much farther as the winter-sports enthusiast skis. 

I've skied the Arlberg on several days over the years, but yesterday, for the first time, did the full trip from St. Anton to Warth and back.  It was a good day for it with mainly clear skies, a good hard freeze allowing the groomers to hold up well except on south aspects, no lift lines, and relatively uncrowded slopes (by Arlberg standards).  I had enough time to not only get to Warth and back, but also to do some side trips to other lifts and villages.

I caught the first Galzigbahn tram at 8:30 and followed the following village-by-village route: St. Anton -> Rauz (not really a village but a place) -> Zurs -> Zug -> Lech (really above Lech) -> Warth -> Lech -> Zurs -> Rauz -> Stuben -> Rauz -> St. Christoph -> St. Anton.

It was one of the biggest days of skiing I've ever had.  When I got back to St. Anton, I had covered in total about 97 km, including lift distances.  I ended up skiing a bit more to get that over 100 km.  In the end Strava suggested a total distance of 103.8 km, total skiing distance of 62.4 km, and total vertical of 12,003 meters.  

Strava has its accuracy limitations, but those number sound good to me so I'm sticking with them.  

There is actually a ski route in the Arlberg known as the Run of Fame that extends from just south of St. Anton to Warth.  What I did was a bit different than that so I'll call it "My Run of Fame."  The actual Run of Fame is 85 km long with 18,000 vertical meters of skiing.  Based on my experience yesterday, one would probably need no lift lines, no breaks, and no turns to accomplish that.  I won't be giving it a try.  

I didn't waste time taking pictures until I got to the top of the Trittkopf II Bahn above Zurs.  I wanted to be at the "tip of the spear" of skiers leaving St. Anton as they can really clog up the liftlines.  However, it was when I got here that I realized it was not going to be a busy day and I could take some photos.

Descending to Zurs. 

One of highlights of the Arlberg, if it is not crowded (and this is rare), is skiing from the top of the Madlochbahn above Zurs to the village of Zug.  There are no lifts near this route so if there aren't many skiers around (a rarity), it has a bit of a quiet feel.  About half way down you can look northeastward down the upper Lechtal to the village of Lech. 

Once above Zug, there's great views of the ski terrain above Lech.  The Steinmahder lift services the attractive but south facing terrain in the photo below.  I did a side excursion to check it out.  

I think did some more skiing and road a bunch of lifts to get to Warth.  

Warth is in the wet northern rim of the Alps and is considered one of the snowier ski areas in Europe.  It also has a predominantly northern aspect.  It felt a bit more like winter here.

At this point I'd been skiing non-stop for three hours, so I stopped for some skiwasser and strudel mit vanillasauce at a mountain hut.  

I've had better, but the calories were appreciated.  

Getting from Lech to Warth or Warth to Lech involves taking a gondola that traverses some flat and convoluted terrain between the two resorts.  The photo below is taken from the top of the lifts above Warth looking back toward the ski terrain above Lech.  I've indicated the gondola with a line labeled "Lech-Warth."  It actually turns to a chondola with interspersed detachable chairs for the last bit of the route (after the bend).  One can also see the upper part of the ski area above Lech, the route from the Madlochbahn to Zug (approximate with Zug blocked by terrain), the lift-served terrain above Zurs, and the route of the Rufikopfbahn cable cars from Lech to the top of the Rufikopf from where one can ski back to Zurs.  

On the gondola ride back to Lech, I was on with a group speaking an unknown language.  The lift stopped for a long time.  At some point someone from the group asked me where I was from in English.  I said Utah.  They then responded "Ah, Alta." Lol.  They were from Sweden, where apparently there is a chapter of Altaholics Anonymous.  We had a good chat.  

After some more skiing I descended into Lech, pictured below.  The valley at center right goes to Zurs.  The Rufikopfbahns ascend the steep avalanche fence covered slope above Lech and then more open terrain to the top of the Rufikopf.  Look closely for the towers.  

From the top of the Rufikopf you ski some of the flattest terrain on the face of the Earth, but you don't care because the scenery is spectacular.   The groomed tracks in the center of the photo are for snow hikers, but the ski trail on the far left is also low angle.  

I did more skiing and rode more lifts.  Eventually I got to Stuben.  This village is less visited and I had long runs to myself there,.  Below is the view from the summit lift looking back toward Zurs, which is in the valley near the center of the photo.  

I then decided to get back to St. Anton to go home, but before doing that I thought I would ski down to St. Christoph so that I visited all of the villages in the Arlberg.  St. Christoph also has sentimental appeal because I stayed here with others from the Salt Lake Olympic Organizing Committee during the 2001 Alpine World Championships.  I'd love to stay there again, but its is well outside of my price range.  

And finally, the descent to St. Anton.  

Another neat thing about this day is that I took the train from Innsbruck to St. Anton.  It's about an hour and fifteen minutes each way and it puts you within about a 5 minute walk of the lifts in St. Anton.  So, from my apartment in Innsbruck to Warth without a personal vehicle.  Very nice.  

Mid-Slope Cumulus

The deep valleys of the Alps are great places to learn mountain meteorology. The have somewhat regular thermally forced valley and slope flows when the large-scale flow is weak and fascinating terrain-forced flows when the large-scale flow is strong.  Clouds are frequently present and are useful for understanding local flow patterns.

Saturday night bought valley rain and mountain snow to western Austria.  Sunday morning I went for a hike above our apartment to a mountain hut.  On the return, I noticed shallow mid-slope cumulus clouds on the south side of the valley, beneath a more layered stratiform cloud that was hovering at higher elevations close to ridgeline.  

The local time was about 1200 so I suspect that surface heating was leading to upslope flow that generated those shallow clouds.  In the wake of the storm, the airmass over the valley was relatively moist and reached saturation with a little ascent to generate the clouds.  Given their shallow nature, the cumulus clouds suggest that the low-level upslope flow was not penetrating all the way to the ridgeline, but was confined to the lower valley atmosphere. 

That's the hypothesis anyway, although it's hard to evaluate with observed data in this case.  

Astounding Forecasts for March

The models are putting out some remarkable height and temperature forecasts for Utah and the southwest US for March.  I'm even a little late getting to the party given that the NWS issued a statement at 2 PM MDT on March 12th for potentially record-breaking temperatures by the middle of next week. 

The synoptic setup is the development of a high-amplitude upper-level ridge over the southwest.  As an example, below is the ECMWF HRES foreacast valid 0000 UTC 20 March (6 PM MDT Thursday) with 500-mb heights above 5940 meters over Arizona and 700-mb temperatures of 10°C over Salt Lake City. 

For the southwest, these are exceptionally high 700-mb temperatures.  The highest March 700-mb temperature every recorded in an upper-air sounding over northern Utah is 8.0°C.  We may be above that for a few days later next week and into the weekend.  The 700-mb temperatures over southern Utah and the desert southwest are also at record levels.  

The seasonal snowpack in the southwest is already on life support.  As of March 12, watersheds in southern Utah, southern Colorado, Arizona, and New Mexico were at or below 50% of median snowpack for the date.  Along the Mogollon Rim, they were below 10%.  

For northern Utah, another perspective is provided by the wet-bulb 0.5°C plumes for Alta-Collins in the lower left of the plot below.  Dramatic warming occurs early next week and in most of the ensemble members this level is above the elevation of the Alta-Collins site (9600 feet) for several days thereafter.  

I saw some online claims of a "miracle March" in Utah because we got some snow to start the month. In reality, there was no miracle.  We got some snow, but not an unusual amount for what we used to call "winter" and now we are going to see the heat big time with a late March sun.  Its not May, but the sun angle is high enough now to do significant damage.  

The mountain snowpack, spring runoff, and Great Salt Lake do not care about hope or wishful thinking.