Particularly on the Main Alpine Ridge towards the south, weak old snowpack layers are still prone to triggering. Slab avalanches of medium size can be triggered by one sole person in places. Danger zones are difficult to recognize, they occur esp. in little-tracked, shady steep terrain. Defensive route selection is crucial.
A weak southern barrier cloud front is forecast to start Friday evening, with intensifying southerly foehn wind. On Sunday, minor precipitation expected. Especially in high-alpine regions, fresh snowdrift accumulations will be generated by the winds, moist/warm air will make the snowpack wetter up to the timberline.
Small likelihood – big consequences
The current situation with regard to the persistent weak layer in the mountains along the Main Alpine Ridge and in particular in East Tirol is most easily summed up with the words “small likelihood – big consequences.” Danger zones for avalanche releases occur seldom, but when a release is provoked, slab avalanches can grow to dangerously large size.
Avalanche prone locations occur especially on steep shady slopes above 2200m. Even for practiced backcountry tourers, these danger zones are difficult to recognize or detect, since the weak layer is often well settled and feels “good” when tracked upon (deeper down it gets harder). Even the well known danger indicators such as settling noises occur seldom. Observations show that a great deal of steep backcountry terrain has been tracked and skied over without any releases occurring. Nevertheless, isolated reports are reaching us of avalanches being triggered by persons, sometimes even remotely triggered.
How to tackle the current persistent weak layer problem is quite simple, yet sobering: ONLY through a suitable, defensive route selection can the risks be reduced. Particularly large, shady steep slopes and terrain which conceal landscape traps should for the moment be avoided.
Bad weather on the weekend – Heightened avalanche danger in the north
As of Friday midday a perturbance will bring high-altitude cloud cover and strengthening southerly foehn wind to North Tirol. On Friday night, winds will intensify and generate fresh snowdrift accumulations at high altitudes which will often be prone to triggering, especially on steep shady slopes in high-alpine zones.
The cloud cover on Friday night will have another effect: the snowpack will have reduced outgoing longwave radiation during the nocturnal hours and so cannot form a melt-freeze crust on the softened snowpack surfaces on sunny slopes. Saturday in North Tirol will be pleasant and mild. Thus, the snowpack will continue to moisten, even shady slopes will become moist up to the timberline. While East Tirol will get some precipitation (snowfall level above 2000m) on Saturday, the weather on Sunday will be wet, in fact “laundry-room weather conditions” with a mixture of sunshine, moist air masses and some precipitation (snowfall level 2000m) are forecast. Amounts of precipitation will be minor.
Starting on Wednesday, 12.03, until Sunday, 16.03, a weather front over Italy brought frequently heavy precipitation, especially south of the Main Alpine Ridge. Winds were generally light-to-moderate. The snowfall level diverged far from the forecast levels.
The warmth in the snowpack generated the formation of a slab which was deposited atop weak, faceted, expansively metamorphosed layers on shady slopes. This resulted in frequently high activity of naturally triggered slab avalanches, even reaching Magnitude 3. The culmination of avalanche activity in East Tirol occurred, according to observers, during the nighttime hours on Saturday and on Sunday (15-16 March). Upon review, this was the highest frequency of naturally triggered avalanches this winter.
Avalanches triggered by persons in the last few days.
During this last week there were several slab avalanches involving persons. Most occurred in East Tirol and were connected to the persistent weak layer referred to above.
14.03.2025 Ternegg, eastern Deferegger Alps; N, 2300m
15.03.2025 Blankenstein, eastern Deferegger Alps; N, 2300m
