Alpine Storm Update

As we sit mired under a ridge in Utah, we look once again to the Alps for interesting mountain weather. 

The storm discussed in prior posts has had quite an impact on the southern Limestone Alps of Austria and northeast Italy.  The Tyrolean newspaper Tiroler Tageszeitung reports level 5 (highest possible) in the East Tyrol, with power outages and mudslides in other areas. 

Source: https://www.tt.com/artikel/30766028/wetterchaos-in-tirol-lawine-auf-haeuser-in-osttirol-strassen-in-nordtirol-gesperrt?slide-id=1

The Tirol Avalanche Report shows level 5 avalanche hazard in the East Tirol and portions of the Dolomites.  Heavy snow also fell along the Carnic Alps further east and south of Villach, Austria, not covered by the Tirol Avalanche Report.

Source: https://avalanche.report/bulletin/latest

In fact, one of the more impressive meteograms I could find was from the Porzehütte, an Austrian Alpine Club hut on the Carnic main ridge south of Obertilliach (red dot below) where the height of the snowpack (HS) climbed from about 20 cm to 199 cm in less than 2 days.  That's a snowfall rate of about a meter (40") per day.  The water equivalent of that snowfall is around 250 mm (10"), so this is some high-density base builder.  

Source: https://www.lawis.at/station/

A look at avalanche reports for mountain areas around Cortina and elsewhere not covered by the avalanche reports above shows level 4 (high) danger.  Snow levels in that area were fairly high.  Observations from Seiser Alm Zallinger at 2055 meters above Val Gardena show temperatures for much of the event hovering near 0˚C.  Snowpack height observations are spotty, but show an increase of about 100 cm.  

Source: https://avalanche.report/weather/stations

At lower elevations, rain and wet snow has fallen.  An example is the village of Castelrotto at about 1000 m.

Source: https://www.seiseralm.it/en/webcams.html

It would be great if we could get a good base builder storm like that.  How about a multi-day storm with 40-70 inches of high density snow and a snow level of around 6500 feet so we can continue COVID hikes in the foothills?  

One can dream.

Contrasts Across the Alps

In the previous post (An Optimistic Snow Forecast) we discussed a developing storm in the southern European Alps, with snowfall developing in the southern Limestone Alps today and becoming heavy through Saturday.

It's worth taking a closer look at the contrast that exists across the Alps during these situations, as when the southern Alps have great upslope, the northern Alps have downslope winds, known as Foehn.

I'm going to use images from two web cams from the great https://www.foto-webcam.eu/ web site. The first is from San Cassiano near Alta Badia in the Dolomites.  The cam faces roughly westnorthwest.  The other is from Seegrube in the Nordkette range above Innsbruck.  The cam faces roughly south and looks toward Brenner Pass and the crest of the Alps.   

Source: maps-for-free.com

With flow from the southern half of the compass, San Cassiano is on the windward side of the Alps for this storm.  Prior to the storm, on December 1st. there was little to no natural snow evident in the area.  

Things are beginning to change, however, and snowcover is evident today, with more on the way.

Meanwhile to the north of the Alps, downslope foehn is developing.  The series of images from Seegrube shows significant change from yesterday when cloud cover filled the Inn Valley and also lingered on the Alpine crest (top photo below).  Overnight, the low clouds cleared out as downslope Foehn developed.  Clouds on the Alpine crest deepened with the increasing southerly flow.  By today, snow was falling on the Alpine crest and spilling over into the mountains and Wipptal (the Wipp Valley, which descends from Brenner Pass), but one can see some sun in Innsbruck. 

This is a very common occurrence in the Alps with stark contrasts from one side to the other during storms.  It does work both ways.  There are situations when the north side gets heavy snow and the south side is dry (see Stau Storm).  In some seasons, one side of the Alps sees more storms than the other, and a quick trip across or under the Alps can lead to better (or worse) snow. 

Knowledge is power, but weather knowledge is powder power.  

An Optimistic Snow Forecast

I knew that headline would get your attention, but sadly it doesn't apply to northern Utah, but instead the European Alps near and south of the Alpine crest.  

The large-scale setup is related to the high-amplitude flow pattern that is dominating the northern hemisphere.  Over the next couple of days, this pattern features an amplifying ridge over the north Atlantic and a deepening trough over western Europe, as depicted in the GFS dynamic tropopause (upper-level) flow forecast for 1200 UTC Saturday 5 December.  

This is a very slow moving pattern that leads to intense water-vapor transport toward the Alps from the Mediterranean and Adriatic Seas.  Such vapor transport is strongly influenced by flow interactions not only with the Alps, but also with the Apennines of Italy and the Dinaric Alps of Croatia and the Balkan States.  This can be seen in the GFS forecasts of 925-mb (roughly 750 meters above sea level) wind, moisture transport (color contours), and 3-hour accumulated precipitation (color fill).  At 1200 UTC 4 December, strong moisture transport is occurring from the south-southwest over the Gulf of Genoa and, due to flow blocking by the Alps, up the Po Valley.  This often leads to heavy precipitation in the region around Lago Maggiore region of northeast Italy and southern Switzerland (white dot).  

A day later, at 1200 UTC 5 December, as the storm shifts eastward, south-southeasterly flow up the Adriatic leads to strong moisture transport toward the Southern Limestone Alps, including the Adamello Alps (blue circle), Ortler Alps (orange circle), and Dolomites (white circle).  These areas will see very heavy precipitation.  

A meteogram for the Dolomites near Canazei shows 184 mm (7.2 inches) of precipitation by 0600 UTC Sunday, most falling since 1200 UTC Friday, with an increase in snow depth of over a meter.  

Enjoy watching a storm in another part of the world if we can't have one here. 

Pathetic Start to December

As "Covember" ends, it's now a lock that July to November was the driest on record in Salt Lake City with only 1.52 inches of precipitation.  It is now one of only three years with less than 2 inches of precipitation during the period, joining 1958 (1.66 inches) and 1933 (1.72 inches).  

Source: NOAA Regional Climate Centers

As far as temperature is concerned, July to November was the 5th warmest on record with an average temperature of 66.7˚F, just a shade behind 2013 (66.9˚F), 2017 (66.9˚F), 2012 (67.1˚F), and 2016 (67.3˚F).  

Source: NOAA Regional Climate Centers

Record low precipitation and excessive warmth is a bad combination and, not surprisingly, the US Drought Monitor has all but far northern Utah in exceptional or extreme drought.  

The trend continues to start December.  believe it or not, there's a cold frontal passage tonight and for that we can be grateful as it will stir up the inversion.  On the inversion, precipitation looks to be scant.  The GFS provides just light amounts in the northern mountains and Uintas.  

The downscaled SREF is actually a bit more optimistic than I am, with 8 members producing 1 to 2.5 inches.  Whoot whoot!  The remaining 18 call for an inch or less.  Sobering reality.  

The forecast beyond that is a complete disaster.  If you want some technical mumble jumble, the large-scale pattern is one characterized by a strong Pacific storm track across the western and central Pacific, with frequent ridge development and anticyclonic wave breaking over the eastern Pacific and Western United States.  For us, that means weak large-scale flow, persistent ridging, and some meandering closed lows over at least the next 8 days.  

Pathetic.

Deflection to Weather West

I'm starting to get lots of questions again about western drought, persistent ridging, and "the blob", the anomalously warm ocean waters in the northeast Pacific Ocean.  

If this is something you are interested in, please see the Weather West blog post "New insights into the Ridiculously Resilient Ridge & North American Winter Dipole" as it should answer most of your questions.  

Time to Ride Again!

For outdoors time, ride is an ambiguous word.  It could me snow riding, the favorite form of recreation for most of the readers of this blog this time of year.  Or, it could mean bike riding, which is also a great activity, but perhaps not the activity of choice in late November or early December.

Unfortunately, the models continue to favor just weak systems moving through the area and forecasts that give us limited mountain snowfall for the next several days.  I'll show a couple of examples.  The GFS forecast below, valid at 1200 UTC 2 December, has a dreaded "Rex Block" parked over the western U.S.  A Rex block features an upper level ridge to the north of a closed low, sometimes referred to as a "high over low block" by those with a Northern Hemisphere bias.  

The Euro isn't much better.  For the same validation time, the ridge/trough amplitudes and positions are a bit different, but overall the pattern is fairly similar.  

As a result, the 6-10 and 8-14 day precipitation outlooks from the Climate Prediction Center are deeply disturbing.  

For skiers, brown means frown.  Thus it's time to ride (bikes) again! 

Addendum at 9:35 AM:

A quick comment that I glossed over tonight.  We might see a bit of mountain snow, maybe a few inches.  Not a game changer, although it might freshen things up a tad.