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.
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| Fresh snow forecast 01.01.-03.01.2021 |
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| 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!
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| 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.
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| 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) |
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).
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| Sequence of crusts and faceted crystals in Virgental (2440m, SW) |
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Lower arrow points to “sandwich of crusts” • Upper arrow to loose snowpack surface;
western Tux Alps (2130m, N) |
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| 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.
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| 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) |
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| Avalanche released on Grosser Leppleskofel; 2650m; NW (photo: Daniel Kleinlercher 31.12.2020) |
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| Avalanche on Frauenwand; western Tux Alps (photo: Hubert Gogl 31.12.2020) |
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| 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.
