Avalanche Warning Service Tirol: Fresh snowdrifts, loose-snow avalanches, still weak old snow regionally

Fresh, trigger-sensitive snowdrifts

The combination of cold temperatures, loose, dry fluffy fresh snow and wind reinforces the forming of trigger-sensitive snowdrift accumulations. These are currently most wide-ranging in East Tirol and the southern Ötztal Alps where recent snowfall was heaviest. With some experience in assessing dangers on-site, these spots are easy to recognize and circumvent. Wherever the fluffy snow is blanketed by freshly generated snowdrifts, superficial naturally triggered small-to-medium sized slab avalanches are possible. Very dry, fluffy powder is a weak layer which reacts with particular ease.

We are entering the coldest phase of this winter (11.02.2021)

Dry, fluffy, very loose powder is now frequent on the snowpack surface. Sellraintal (photo: 11.02.2021)

Snowfall on 10-11 February often was deposited on very loose, fluffy powder

Most of the snow last week came, once again, in the south. Here, on 06.02.-08.02.2021)

Snow plumes in central East Tirol (photo: 11.02.2021)

Worth mentioning: apart from wind impact, the powder snow is highly enjoyable.

Descent in powder, western Kitzbühel Alps (photo: 11.02.2021)

A brief threat: loose-snow avalanches in extremely steep terrain

The radiation in mid-February is already intense. Despite low temperatures it rapidly generates expansive metamorphosis of the snow crystals. In extremely steep terrain this can cause snow crystals to lose their equilibrium, the impulse of which is passed on to neighboring crystals, etc. That is the start of a loose-snow avalanche. Most remain small-sized. In the Gurgler Massif (40 cm fresh snow on 10-11 February) and in East Tirol they can grow larger.

As soon as solar radiation intensifies: small loose-snow avalanches in extremely steep terrain. Western Kitzbühel Alps (photo: 11.02.2021)

A continuing theme: weak old-snow regionally

Comparing the number of reported avalanches which involved persons each week since mid-January, they are decreasing further. This is an indication that the snowpack has lower proneness to triggering. Nevertheless, slab avalanches still trigger in the weak old-snow, particularly when the weight of skiers hits the snowpack on steep slopes. Most often, the avalanches unleash where the snow is shallow. As a rule, it is the weak layer we are well aware of: formed during the cold phase in early January, combined with a melt-freeze crust which formed just before Christmas. Increasingly, it strikes on west and east-facing slopes, in isolated cases on north-facing slopes, in a narrow altitude band between 2000 and 2400 m.

A translucent snow profile from the Idalpe zone, Silvretta, at 2250 m. Visible in the upper part: a slightly brownish layer, the recently deposited dust from the Sahara desert. Near ground level is a rough-grained potential weak layer for avalanches.

Avalanche Kahorn, Defereggen: the avalanche was probably remotely triggered by a group just above the fracture. No one was buried. 2300 m, east (photo: 06.02.2021)

Avalanche Sattelgrat, south of St. Anton am Arlberg. Visible: 4 persons. No injuries. W/NW, about 2200 m (photo: 11.02.2021)

Avalanche towards Kemater Alm, about 2300 m, Stubai Alps (photo: 08.02.2021)

Danger pattern cold-on-warm (dp.4) - without near-surface weak layer regionally

Following a mild, sunny, foehn-wind impacted weather phase up to 7 February, the snowpack surface was moistened up to nearly 3000 m on very steep, sunny slopes. Rainfall on 7 February caused the snowpack at low and intermediate altitudes to become thoroughly wet in all aspects, superficially at very least.

Reported rainfall levels in Tirol on 07.02.2021

On the evening of 7 February a cold front moved in from the northwest, temperatures dropped noticeably. There was also snowfall. Suddenly the prerequisites for Danger Pattern dp.4 (cold-on-warm) were there.

The arrow points to the beginning of a potential weak layer being formed due to dp.4

Since this is so, we have been searching for new potential weak layers near the surface. Our latest findings: we currently think that a thin, faceted / faceted-decomposed snow weak layer is increasingly to be found on north-facing slopes at 1800-2300 m. A report points to its presence at about 2200m, E/SE. In Northern Tirol, the “slab” is currently lacking, so that a triggering seems unlikely (or the slab will be small). In East Tirol and the Gurgler Massif, these weak layers could well be quite relevant, since they are covered more deeply.

Snow profile Schlick: the arrow points to a recently formed weak layer due to dp.4. When blanketed by bonded snow, slabs are easily possible. For further snow profiles, see - lawis.at

Shallow avalanche fracture, possibly due to dp.4, western Tux Alps, about 2200 m, E/SE (photo: 08.02.2021)

Dust from the Sahara

The dust blown northwards from the Sahara desert last week was pretty impressive. Skies were actually darkened in some places. As a result of the precipitation which followed, it was deposited on the snowpack. In many places, you now see a thin layer inside the snowpack, compliments of the desert.