First things first: strong winds are generating mostly small, often trigger-sensitive snowdrift accumulations at high altitudes. Caution urged especially on shady, steep slopes.
A cold front on 19-20. November brought generally 10-20 cm of fresh snow, locally a bit more.
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| Fresh snow: 19-20.11.2020 |
Plus, in major areas of precipitation along the Main Alpine Ridge, strong winds are blowing, transporting the fresh snow.
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| Noteworthy: strong northerly winds prevail since the cold front moved in. Eselrücken measuring station in East Tirolean Tauern. |
Freshly drifted snow masses are the problem, particularly on shady, steep slopes. This is due to the structure of the uppermost snowpack layers from the last bout of snowfall: frequently a series of thin, soft layers and hardened crusts.
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| Snow profile, 18 November, N, 2530m, 35°, Pirchkogel in Stubai Alps. The uppermost (already metamorphosed) layer stems from the snowfall on 16.11.2020. The crust beneath it formed on 3-4 November during the spurt of rainfall and subsequent moist air masses. During the long period of fine weather starting on 5 November, a further loosely-packed layer formed beneath the thin crust consisting of faceted crystals and depth hoar. When this is covered by fresh drifts, the upper layers become avalanche-relevant weak layers. |
Moreover, on north-facing ridgeline slopes, Nigg-Effect was evident during the long period of fine weather: in a 50-100 meter altitude band, surface hoar formed. In places where the wind did not have much effect (which dissolved the weak layer) at the start of the last round of precipitation, caution is urged.
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| Surface hoar generating through Nigg Effect. Zwieselbacher Rosskogel, Stubai Alps (photo: 15.11.2020) |
On the other hand, the snowpack surface on sunny slopes was generally hard and stable. Currently, only there does the loose, blanketed fresh powder form a possible weak layer beneath fresh snowdrift accumulations, and even this is the case only at high altitudes and for a short period (today, 21.11). In addition, solar radiation will trigger a few loose-snow avalanches.
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| Stable snowpack on sunny slopes on 18 November at about 2700 m (Zillertal Alps) |
Danger: snow-covered plates of ice
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| Ice plate in Wildlahnertal (photo: 18.11.2020) |
October rounded to a close in moist, cool, rather gloomy ways with lots of fresh snow in the mountains around 26.10 (National Holiday). A powerful cold front brought lots of snow at the end of the month. Subsequently November ushered in mild, generally sunny weather with brief perturbances on 3, 4, 12, 16 November).
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| Cold fronts are encircled in black. A stable phase of high pressure settled in at the start of November. Thereafter it was repeatedly windy. |
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| Start of fine weather period in November. The fog and moist air masses receded. A melt-freeze crust mostly capable of bearing loads formed due to extensive surface moistening of the snowpack up to high altitudes. Thereafter it got increasingly thinner. |
The next blog will appear as soon as conditions starkly change.
