Dangerous conditions for winter sports enthusiasts. A skiers “high” !

Highly trigger-sensitive snowpack. Danger conditions for winter sports enthusiasts, with high risk of accidents. For that reason, please: exercise high restraint in the next few days!!!

The swift rise in avalanche danger referred to in the last blog  has now occurred. Reports from our observers and from winter sports enthusiasts confirm the very high trigger-sensitivity of the snowpack in wind-impacted regions and in general in regions where snowfall has been heavy. Fracture cracks, settling noises and the first naturally triggered slab avalanches are part of the daily agenda. As of the second bout of precipitation since the evening hours (on 13 January) snowfall amounting to 30-50 cm of fresh snow has been registered, less in the eastern regions and in southern East Tirol, plus storm-strength winds in the mountains, which will increase the frequency of naturally triggered releases.

For that reason, avalanche danger has been ranked at HIGH in many regions. This is a so-called skiers’ high, meaning that there are many avalanche prone locations with a high likelihood of triggering. Very large avalanches with risk of damages are not expected in the present forecast. But area-wide avalanches with deep fracture zones and large runout zones are to be expected.

Danger level map for 14.01.2021

Avalanche prone locations are found at very least above the timberline, but also in sparsely wooded zones wherever there is an area-wide snowpack. Only there, where there was snow before the current snowfall, conditions are better. For that reason, there is only Danger Level 2 at lower altitudes. But we must point out in this connection that danger level borders are flowing, not clear-cut, therefore, please be careful in the eastern regions of North Tirol.

Fresh slab avalanche in Ötztal Alps (photo: 13.01.2021) 

 

Fresh slab in sparsely wooded zone. Ausserfern (photo: (c) Stefan Zangerl)

A view beneath the fresh snow masses. Near the upper glove: weak layer of loose, faceted crystals; beneath that, a thin melt-freeze crust from 21-22 December, beneath that, a loosely-packed weak layer of faceted snow crystals. Stability tests snow that the snowpack is currently unbelievably trigger-sensitive. Initial fractures progagate very easily inside the test-block. Muttekopf region (photo: 13.01.2021) 

Sum of fresh snow, first round, on 12-13 January 

Snowfall and storm winds in the mountains, an unfavourable combination when the snowpack is weak. Ulmerhütte, Arlberg region

Massive snow transport. Thereby: numerous snowdrift accumulations generated, also here in the Kühtai, 13.01.2021 (photo: (c) Nicolas Metz)

The most perilous days of the winter so far!

Since we now face the most dangerous days of the winter so far, for all winter sports enthusiasts we would like to issue the following message: the current situation demands extreme restraint and highly precise knowledge of local terrain in backcountry areas.

Snowfall following long cold snap – a dangerous situation

An abrupt end to a highly favourable avalanche situation

 Right at the start an important message for all winter sports enthusiasts: as a result of the forecast snowfall between today, 12 January and Thursday, 14 January, including wind impact, avalanche danger levels will increase very swiftly. This is especially because of the effects the long period of cold had on the snowpack. Uppermost layers are expansively metamorphosed (faceted) over widespread areas and frequently consist of surface hoar, faceted and/or loosely-packed decomposed snow crystals. In addition, there is often a near-to-surface sequence of thin crusts and soft layers. In the northern regions there are also weak layers evident at ground level. All in all, we are burdened by a number of extremely weak layers which will get fresh snow and freshly generated snowdrifts on top of them.

 

Surface hoar on Hochzeiger (photo: 07.01.2021)

Surface hoar has been reported throughout Tirol

Backcountry tour in East Tirol: loosely-packed snowpack surface (photo: 07.01.2021)

Visible in the snow profile are several potential weak layyers: a slab in the form of fresh snow and drifts is the only thing lacking (Ausserfern, Jöchlspitze - profile from 10.01.2021)

Experience has shown that snowfall plus wind impact following a long period of cold weather is always particularly dangerous. That means we can expect over the coming days numerous naturally triggered, generally medium sized, in western regions of North Tirol also large-sized, slab avalanches as well as with a high likelihood of triggering avalanches by winter sports enthusiasts.

 

72-hr forecast of fresh snowfall

Winds are intensifying...

 

...winds are currently transporting snow at high altitudes, generating snowdrift accumulations which are increasingly prone to triggering (station Eselrücken-Kreuzspitze in central East Tirol)

 

Therefore: we advise great caution and a high degree of restraint!

The next update of the blog will be published at latest Thursday evening, 14 January 2021.

Caution in southern regions: weak near-surface layers

 Most of the current avalanche prone locations: in East Tirol and south of Gurgler Group

Snowpack analysis and reports from observers confirm that slab avalanches can currently be triggered by winter sports enthusiasts in near-surface layers above all else.

Near-surface weak layer, east-facing slope at 2450 m in Villgratental. Avalanche accident Pürglers Kunke on 06.02.2021 (photo: 07.01.2021)

Most unfavourable of all currently are steep slopes in E-S-W aspects between 2300 and 2600 m. In that altitude band there is frequently a thin layer of loosely-packed, predominantly faceted crystals (also surface hoar) beneath the melt-freeze crust which formed just before Christmas. Most recent avalanches were triggered in this loose layer. 

Avalanche Pürglers Kunke on 06.01.2021; E, 2450 m (photo: LWD Tirol on 07.01.2021)

 One of several slab avalanches which triggered recently in Hochgurgl. Avalanche on 03.01.2021
(photo: 04.01.2021 

An overview of other recent avalanches, including those registered at headquarters, can be found at lawis.at. 

On shady slopes the surface hoar inside the snowpack can most easily be triggered by large additional loading on very steep slopes. All signs point to this being the case only in few spots, most frequently in a small altitude band around 2200 m and in ridgeline terrain (possibly Nigg Effect?)

Blanketed surface hoar in western Tux Alps. Stability tests showed that this layer was no longer triggerable. (photo: 04.01.2021) 

Danger of glide-snow avalanches

Whoever studies glide-snow avalanches knows that they can even trigger in the middle of the night on the coldest day of winter. Currently it is cold, and currently we observe more and more glide-snow avalanches in East Tirol where there is a great deal of snow. They can still bury sections of roads; they can still place backcountry skiers at risk.

In remaining North Tirol, increasing danger zones on shady slopes where snow is shallow

Apart from the regions which recently got so much snowfall, the general avalanche situation is quite favourable. Avalanche prone locations are found primarily on very steep shady slopes in transitions from shallow to deep snow. In those places avalanches can be triggered primarily by large additional loading. The danger zones are not widespread, the releases small-to-medium size.

Characteristic of the current situation in far-reaching areas of North Tirol is a heavily wind-impacted snowpack surface. Also typical is a comparatively shallow snowpack, especially in northern and northeastern regions.

A very characteristic photo in northern regions: a wind-impacted snow cover; northern Stubai Alps (photo: 31.12.2020)

Little snow in North Tirol’s Lower Inn Valley (photo: 02.01.2021)

Snow distribution in Tirol

Snow distribution in Tirol: lots of snow in the south, little in the north

 In southern East Tirol we currently are above the maximum snow depths ever measured (since 1960).

An arduous task: shoveling snow from a rooftop. Lienzer basin (photo: 04.01.2021)

Short review of an avalanche-active period, beginning of January 2021

For a short spell, we assigned high avalanche danger to southern East Tirol at the beginning of the year (3-4 January) due to intense snowfall. To round out our last blog, here are a few images.

Typical: many shallow, but sprawling avalanches, Grantspitz Group (photo: 03.01.2021)

Hillside avalanche in Defereggental. Not only road sectors, also playing children were endangered. (photo: 02.01.2021)

Snow released in extremely steep terrain, buried the Felbertauern Road. The repair work is here underway. (photo: 02.01.2021)

Naturally triggered slab avalanche over surface hoar in the Carnic Alps (photo:; 03.01.2021)

New snow in south. Newly delicate avalanche situation for backcountry skiers. Anew: great restraint called for!

Treacherous situation for winter sports enthusiasts in East Tirol. Snowpack is highly prone to triggering!

In East Tirol there is a situation similar to that of 28 December when snowfall and strong winds were forecast to strike the southern regions. Accordingly, an avalanche situation which is already delicate is being ratcheted up another degree. It’s clear as day: winter sports enthusiasts need to exercise a great deal of restraint! We assess the danger starting on 2nd January as a result of the intensified precipitation during the morning hours at “high-3” (upper level of Considerable). Due to the lesser amounts of fresh snow forecast than on 28 December, we assume it will not reach the “Skiers High” we touched then, but we’ll come quite close (high trigger sensitivity, widespread danger zones, naturally-triggered small-to-medium avalanches). The ultimate rank depends on the actual amounts of fresh snow: according to latest forecasts, exceeding 30 cm only in certain spots.

Fresh snow forecast  01.01.-03.01.2021

Wind forecast at climax of precipitation intensity. Winds will be southerly.

A complex situation

Through the highly variable weather, the snowpack situation is becoming more and more complex. This applies to the uppermost weak layers in regions where recent snowfall has been heaviest; and to the ground-level weak layers in North Tirol where snow is shallow.

• Surface hoar and diamond powder on the surface

Currently (1 January) the snowpack surface, particularly in East Tirol, is loosely-packed and often consists of diamond powder (extremely cold, light, fluffy powder). This occurred because in the final phase of the snowfall on 29 December the stormy wind suddenly stopped. In addition, surface hoar has formed widespread since then. Both these phenomena are extremely reactive weak layers. And both were shortly thereafter blanketed by fresh drifts!

Surface hoar on Carnic Ridge (photo: 01.01.2021 von Gerhard Figl)

• Surface hoar already blanketed by fresh snow

The recent bout of fresh snow from 28-29 December was deposited on top of still trigger-sensitive surface hoar in places. The diamond powder on top of that has probably settled and stabilized in the interim.

A typical snow profile from the northern regions: Ausserfern, little snow, weak layer at ground level; surface loose in wind-protected zones. Encircled: the surface hoar and the blanketed surface hoar. (1120m, South)

•  “Sandwich of crusts”

Furthermore, the phase of warm weather before Christmas, including rainfall on 21-22 December, also plays a part. Thereby, a quite trigger-sensitive layer of thin crusts and loosely-packed faceted crystals was generated. Based on latest information, there is heightened proneness of the snowpack to trigger on north-facing slopes between about 2100 and 2300 m, in isolated cases extending up to 2500 m; and in the other aspects between about 2200 and 2300 m. In southern and central East Tirol, on the other hand, only the forest edges on north-facing slopes are at risk due to the lower rainfall level (max. 2000 m).

Sequence of crusts and faceted crystals in Virgental (2440m, SW)

Lower arrow points to “sandwich of crusts” • Upper arrow to loose snowpack surface;
western Tux Alps (2130m, N)

Deceptive: blanketed snow dunes. Deferegger peaks. (photo: Daniel Kleinlercher 30.12.2020)

Photos of recent avalanches

To repeat: we anticipate a situation similar to that of 28.12. Pictures like the ones below may will be shot after the presently forecast snowfall.

Small naturally triggered slab avalanche, typical for a highly reactive weak layer, e.g. surface hoar or diamond powder. Brunnalm (photo: Daniel Kleinlercher 31.12.2020)

Avalanche released on Grosser Leppleskofel; 2650m; NW (photo: Daniel Kleinlercher 31.12.2020)

Avalanche on Frauenwand; western Tux Alps (photo: Hubert Gogl 31.12.2020)

Slab released on Schönbergspitze, central East Tirol (photo: Elisabeth Steurer 30.12.2020)

The further you go north...

...the less it has snowed recently, the more intense wind impact on the snowpack surface is...and the worse skiing conditions are.

In northern regions the snowdrift problem is comparatively minor, but there is an old-snow problem at ground level. Weak ground-level layers are probably triggerable only by large additional loading where the snow is shallow on steep slopes. This applies especially to shady terrain above about 2200 m.

Several avalanches involving persons - no injuries - restraint still imperative

 Avalanche reports from Tirol headquarters

Since yesterday, 29 December, headquarters has received information about 8 avalanches involving persons:

29.12.2020: Juifenalm (northern Stubai Alps); Rosskopf (eastern Tux Alps); Angerbergkopf (northern Stubai Alps)

30.12.2020: Kleiner Leppleskofel (east. Defereggen mountains); Grosser Leppleskofel (east. Defereggen mountains); Rogötzllenke (east. Defereggen mountains); Muttenjoch (central Stubai Alps); Schönbergspitze (east. Defereggen mountains)

All these avalanches unleashed without injuries. According to latest information they were medium-sized slab avalanches, focal point in the Defereggen mountains

Violet dots: large area of avalanches in Defereggen mountains on 30 December

Continuing: serious avalanche situation, particularly in southern regions 

We have reduced the danger level for tomorrow (New Year’s Eve) from high to considerable, but in the southern regions we anticipate a delicate situation for skiers. Particularly where surface hoar is blanketed by snowdrifts, the drifted masses can be easily triggered by minimum additional loading. Today we received reports of settling noises, fracture cracks and remote triggerings, whereas naturally triggered avalanches were not observed. Quite fitting for these observations are two photos of an exemplary route selection and behavior adapted to the present situation.

Tour in flat to moderately-steep terrain near Golzentipp (Carnic Ridge) - (photo: 30.12.2020)

Arrow: a backcountry skier ends his tour at this point, before it gets steeper. Hoher Bösring - Carnic Ridge (photo: 30.12.2020)

Further north, caution urged towards fresh drifts, also towards trigger-sensitive old snow

On Monday night (28-29 December) there was far less in the northern regions, the amounts of snowfall gradually decreasing towards the north. Snowdrift accumulations are thus shallower than in the south. Nevertheless, the snowpack, at least above the timberline, is impacted by winds also there.

Wind sculpture generated by intensive wind force. Ötztal Alps (photo: 29.12.2020)

Hard slabs

Caution: precisely during storm-velocity cold phases, so-called hard slabs can be triggered increasingly frequently in steep terrain. The snowpack surface can sometimes be hard as steel. This has to do with the heightened brittleness of the slabs due to the low temperature. And of course a marked weak layer is an important element of such a hard slab. That can be found in transitions from shallow to deep snow and where the snow is shallow.

 

Snow lumps point to hardened slabs, Nauders mountains (photo: Hans Hofer, passed on by Florian Maas)

Outlook: first step into the new year

The ZAMG Weather Service has released new information for precipitation in the southern regions. For the first 3 days of the new year, about 30-50 cm of fresh snow can be expected in East Tirol, focal point will again be in the furthermost southern regions.

Thus, delicate avalanche conditions can again be expected for backcountry tourers. Winter sports enthusiasts need extremely good avalanche knowledge and restraint when they are in outlying terrain.

We wish one and all Happy New Year and many safe adventures in the wintery mountains. 

Yours, the Avalanche Service team of Tirol