Isolated danger spots: small, easily recognized snowdrifts

Isolated danger spots: small, easily recognized snowdrifts
 
For backcountry skiing and freeriding tours, in most parts of the countryside there is still not enough snow. Only along the Main Alpine Ridge are we receiving reports of high-altitude, mostly shady slopes where conditions are acceptable.

Wintery conditions on shady slopes at high altitude as above, south of the Venediger Group. (Photo: 28.11.2018) 

Far less snow on south-facing slopes (Photo: 28.11.2018) 

Powder snow good enough for skiing is found on shady slopes at high altitudes, and practically nowhere else. Most often it was deposited on top of an old snowpack capable of bearing loads stemming from the last rounds of snowfall, e.g. 19.11, 23+24/11 and 27/11.2018.

Precipitation and development of snow depths last week in Kühtai.

The snowfall on 27.11 was to a greater extent in North Tirol, on 23.11 more in South Tirol.

Powder snow in the vicinity of the Stubai Glacier (Photo: 28.11.2018) 

Powder snow deep in the Ötztal (Photo: 28.11.2018) 

View towards Galzig, Arlberg region, before the snowfall of 27.11 (Photo: 26.11.2018) 

View towards Galzig, Arlberg region, following snowfall of 27.11 (Photo: 28.11.2018) 

View towards Galzig, Arlberg region: rising temperatures plus solar radiation amplify snowmelt (Photo: 29.11.2018) 

As the weather fronts passed through, winds from varying directions prevailed, sometimes blowing at strong velocity.

 A wind-exposed spot: the Patscherkofel, south of Innsbruck. Initially, southerly winds prevailed, shifting to northerly on 26.11 as temperatures dropped. Then another shift to southerly.

Small, rather isolated snowdrifts accumulated at high altitude, some of which can be triggered (on steep, shady slopes). With experience, these drifts can be easily recognized and circumvented.

Studying the snowpack a bit more closely, the words from the last blog still apply: weak layers exist, it is currently possible but unlikely that they will unleash.

A sequence of crusts and unbonded layers near the upper surface is currently not a problem, but we have to keep an eye on it. Stubai Glacier. (Photo: 28.11.2018) 

Thus, in the regions with ample snow, favourable conditions still prevail. The danger from rocks and stones is more threatening than from avalanches. Otherwise worthy of mention: last week was used for technical snow production.

Snow cannons full throttle in Kühtai. Skiing operations will be launched this weekend. (Photo: 28.11.2018) 

After a roller-coaster week, winter draws nearer

After a roller-coaster week, winter draws nearer

Highly variable conditions have prevailed during the last week. Repeated bouts of rainfall or snowfall occurred The snowfall level lay between 2000 and 2800 m. At high altitude, the winds intensified measurably, blowing from westerly directions.

Example of variable weather conditions at the Nachtweide-Palinkopf station (Silvretta Group)

Alternating sunshine and clouds on the Grossglockner

Most of the snow fell in the western regions, e.g. here in the vicinity of Nauders (Photo: 03.12.2018)

Wind map of 04.12.2018; winds were blowing predominantly from the west

The high-altitude powder snow referred to in the last blog became a rarity as a consequence of the wind. The snowpack surface turned erratic, and the frequency of snowdrift accumulations increased incrementally. These snowdrift accumulations were generally small-sized, but in isolated cases could be triggered by large additional loading.

A skier triggered a small mass of drifted snow on the Stubai Glacier The weak layer was the covered powder snow. (Photo: 03.12.2018)

A heavily wind-impacted snowpack surface on the Rettenbachferner glacier (Photo: 05.12.2018)

The current situation in North and East Tirol permits backcountry skiing tours only to a very limited degree. Most of the snow which has fallen was deposited on the Main Alpine Ridge between the Ötztal Alps and the Hohe Tauern. A cohesive area-wide snowpack is evident predominantly above approximately 2200 to 2400 m. In the remaining parts of the land, there is still not enough snow for skiing tours in outlying terrain away from secured and marked ski runs.

The snow situation along the Main Alpine Ridge above approximately 2200 to 2400 m is quite good...

...but away from the Main Alpine Ridge there is still only a little snow, like here in East Tirol (Photo: 04.12.2018)

Particularly where as a consequence of the intensive precipitation at the end of October there was a large amount of snowfall, a solid snowpack base is evident. Crusts and unbonded weak layers are found only near the upper surface, by and large. Whereas in other regions the snowpack is often unfavourably layered due to the shallow snow and the faceted snow crystals generated by expansive metamorphosis, leading to pronounced weak layers.

Snow profile Vordere Schwenzerspitz in the Gurgler Group from 05.12.2018; west, 2800m, 30°. A compact snow base with a few crusts in the upper part of the snowpack. All in all, a very solid structure for future loading in the form of fresh snow (© Nicolas Metz).

 

Snow profile on Hoarberger Kar in the eastern Tux Alps from 02.12.2018; north, 2400m, 30°. A snow profile distinguished by ongoing switches of warm and cold: the crusts were formed through the impact of high temperatures and rain. During clear, cold days and nights, the expansive metamorphosis generated weak layers at ground level between the crusts. To date, a relevant amount of snow is still lacking to form a “slab” for the triggering of a slab avalanche. (© Florian Wechselberger).

What happens next?
On Friday night, a cold front will reach us from the northwest which will be accompanied by storm-strength winds and bring the first snowfall. The snowfall level will drop to nearly 1000 m. In the following days, snowfall over widespread areas will spread throughout Tirol, with steadily dropping snowfall levels. The major area of precipitation will be in the typical northern barrier zones. In East Tirol, especially in the southern parts, significantly less snowfall is anticipated.
As a result of snowfall and wind, the avalanche danger levels will increase over widespread areas.

Fresh snow forecast until Tuesday morning, 11 December

A first analysis of the snowpack

The winter to date

At this juncture of the season, winter has been launched only at high/high-alpine altitudes in the southern regions of the land. It was generated by intensive precipitation at the end of October. As we know, this precipitation was accompanied by thunderstorms which led to mudslides, flooding and far-reaching windstorms in southern regions.

A glance at the high-altitude automated weather station on the Pitztal glacier in the Ötztal Alps helps to encapsulate recent weather events: the first bouts of snowfall significant for the snowpack occurred on 24.09, 01.10 and then from 24.10.2018. Extensive periods of fine weather starting at the beginning of October stand out, as do inordinate amounts of precipitation, including storm-strength winds, at the end of October.

Ground-level weak layer

To achieve a penetrating snowpack analysis it is always important to follow developments immediately following the first snowfall in autumn. The mountains turned white for the first time on 25.08.2018 (a cold front terminated the fifth-warmest August in measured history). This snow swiftly melted, which in many places also happened after the bouts of snowfall which followed on 01.09, 07.09, 24.09 and on 01.10.

Briefly dusted with snow, rapidly laid bare. View from Nebelhorn in Oberstdorf towards the SE on 02.10.2018  (© foto-webcam.eu) 

In far-ranging parts of Tirol there was no autumnal snow to be seen (following a three-week long period of fine weather). View from Nebelhorn in Oberstdorf towards the SE on 26.10.2018 (© foto-webcam.eu) 

However, this was not the case in high alpine, particularly in glaciated and, further, shady terrain. There the snow remained on the ground, despite the unusually sunny and warm month of October (10th-warmest October in measured history). On the surface, a more or less thick melt-freeze crust frequently formed. Beneath that, the snow began to metamorphose, i.e. it become loosely-packed, forfeited its bonding. Upshot: at the fundament in several snow profiles there are loose, faceted snow crystals, depth hoar in other words, potential weak layers for slab avalanches.

Snow profile on Kraspesferner glacier in the Stubai Alps on 04.11.2018; north, 2935m, 22°. The ground-level, loose layer is recognizable. The ice film stems from the period of snowfall before 02.10,  was generated during the following 3-week period of fine weather. (© Lukas Ruetz)  

Snow profile on Hintertux Glacier in the Zillertal Alps on 15.11.2018; NW, 3070m, 38°. Similar to the previous profile, beneath the hardened crust, the loosely-packed ground-level depth hoar is visible. (© Stephan Mitter) 

In isolated cases, this ground-level weak layer triggered slab avalanches.

Slab avalanche which was unleashed from a ground-level weak layer (atop glacial ice) during the storm-ridden period of precipitation at the end of October, below the Grundschartner in the Zillertal Alps. (Photo: 18.11.2018) 

Sequence of crusts and loosely-packed layers near the surface

Also significant are the developments in the layers near the uppermost surface starting at about 2500 m altitude. Within the first 10-30 cm a sequence of crusts and loose crystals can be found. The crusts were generated by rainfall frequently extending up to 2700 m, from place to place as high as 3000 m. They were formed on sunny slopes, and also through the impact of solar radiation and warmth.

Snow profile at Tuxerfernerhaus in the Zillertal Alps on 15.11.2018; north, 2660m, 25°. The sequence of crusts and loose crystals resulted from fluctuating temperatures accompanied by snow and rainfall during the period of bad weather starting on 27.10, along with the snow metamorphosis process which immediately followed. (© Walter Würtl)  

Snow profile on Riepenkees in the Zillertal Alps on 15.11.2018; east, 2810m, 33°. Also here, the sequence of crusts and loose snow crystals is evident in the layers nearest to the surface. The lower snowpack is compact (© Peter Bletzacher)  

In isolated cases, stepping onto a snowpack with that layering caused glide cracks to become visible or else settling noises could be heard.

A loosely-packed layer about 10 cm beneath the surface bordering on a crust was disturbed when one stepped on it. The result: settling noises and glide crack formation. This was observed increasingly in flattish and sunny terrain at altitudes between about 2500 and 2800 m. Southern Ötztal Alps; 14.11.2018 (© Hugo Reindl) 

During a stability test near the Hintertuxer Glacier, this superficial mass of snow was triggered (Photo: 16.11.2018) 

Viewing automated weather station graphs aids interpreting these superficial layers:

Three weather station graphs from disparate locations: Jamtal refuge on Main Alpine Ridge, Hochfilzen in the northern regions and Assling in the southern regions. We focus primarily on the two upper graphs of the Jamtal refuge: the up and down of snow depths corresponds to the rise and fall of air temperatures. Rainfall on 27.10, then snowfall on 28.10, which turned to rain (snow depths diminished). Then on 29.10 and 30.10 a new round of snowfall and rain. What stands out is also the north-south gradient in the amounts of precipitation (for purposes of comparison, the various scales need to be given due consideration).

First avalanches involving persons

On the Rettenbachferner glacier in the southern Ötztal Alps the first avalanches involving persons were registered. Twice (on 31.10 and 03.11) persons triggered avalanches, but were not swept along.

Avalanche unleashed on Rettenbachferner glacier on 03.11.2018. The avalanche fractured all the way down to the glacier ice. (Photo: 03.11.2018) 

Snow profile of the avalanche Rettenbachferner glacier on 03.11.2018, NE, 2980m, 34°. Complex sequence of layers. (© Lukas Ruetz) 

Weather station graphs from Rettenbachferner glacier. Significant for the avalanches was the snowfall starting on 27.10 (the prior snowfall, which brought super-powder to high altitudes, is also visible).

Nonetheless, at the present time predominantly favourable conditions all in all

Even though at certain altitudes and in certain aspects, potentially weak layers for slab avalanches occur, a quite favourable situation prevails in general. There are two reasons for this:

The ground-level weak layers are frequently covered over by compacted layers, so that a disturbance by winter sports participants appears unlikely.

On the other hand, in the uppermost layers of the snowpack the minor blanketing of snow has little impact. What matters for the “slab” of a slab avalanche is a sufficiently large amount of snow atop the weak layer. And that is currently lacking.

In high alpine regions the snowpack has often been massively impacted by winds and is thus hardened, e.g. here on the Daunkoglferner glacier in the Stubai Alps. (Photo: 14.11.2018) 

Sand-dust from the Sahara

Whoever digs down into the snow cover will often bump into a yellow layer. This is sand-dust from the Sahara which was massively deposited by the precipitation around 29.10.

Sand from the Sahara which spread northwards

The yellow layer at the edge of the ski run in Hochgurgl was tinted by Sahara sand. (Photo: 15.11.2018) 

Snow cannons

The first half of November has once again proved to be unseasonably warm. Only when the temperatures receded starting on 17.11 did the snow cannons get a chance to operate. According to media reports, for example, currently 1,240 snow cannons are currently operating in the Silvretta Skiarena in Ischgl. To date they have generated 800,000 m³ of snow, requiring 300,000 m³ of water as raw material. Today, on 22.11, the ski season is being launched there.

Snow cannons are operating at full throttle in Tirol. View from Rofan towards the south. (Photo: 18.11.2018) 

Technical snow also in neighbouring Bavaria (Photo: 21.11.2018) © foto-webcam.eu

A few additional impressions…

Launch of the ski-touring season in East Tirol for all those willing to carry their skis up to about 2300 m altitude. (Photo: 14.11.2018) 

Corn snow in early winter, East Tirol (Photo: 12.11.2018)

Powder from 19.11. in the southern Ötztal Alps (Photo: 20.11.2018)

Surface hoar near ridgline on a shady slope above Serfaus (Photo: 12.11.2018) 

A not unusual sight: snow-padded summit cross on the Main Alpine Ridge (Photo: 08.11.2018) 

The main reason for this snow-padding: moist air masses and stormy winds. It’s not at all unusual that winds at the weather stations reach 150 km/hr in gusts, in some cases, as at this station in the southern Ötztal Alps, velocities of nearly 200 km/hr have been measured.

(This report was compiled with the assistance of apprentice Michael Reisecke.)