Caution: near-to-surface snowdrifts
Above 2000m, considerable avalanche danger currently (19.03) prevails. This is due to recently generated snowdrift accumulations which can often be triggered by minimum additional loading in very steep terrain. They occur in all aspects and are difficult to evaluate, partly because of the powder layer on top of them (since the last snowfall was deposited without much wind impact). This will make the next few days difficult, since a brief period of poor visibility awaits us.
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Typical of recent days in far-reaching parts of North Tirol and northern East Tirol:
snowfall + wind + poor visibility. Mieming Massif (photo: 17.03.2021) |
April weather: both positive and negative, as regards avalanche danger
We are currently observing an interesting interplay of instable weather, snowfall and/or graupel showers (often heavy) and bright intervals including intensive (diffuse) solar radiation. The third factor has a positive effect at intermediate altitudes in particular, also in the regions where there is less snow. There, potential weak layers inside the snowpack consolidate/interconnect rapidly. In the regions where recent snowfall has been heaviest and at high altitudes, on the other hand, solar radiation can create bonding of the uppermost layers and thereby raise the likelihood of slab avalanches triggering.
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| April weather in March: in foreground, snowfall; in background, the sun is shining. Solar radiation is intensive, despite the unseasonably low temperatures. Inn Valley (photo: 18.03.2021) |
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| One of the hot-spots in recent snowfall in Tirol: Seegrube, above Innsbruck. In the interim, the settling process of the snowpack has “overtaken” the arrival of fresh snow. |
Recent snowpack analysis
As mentioned in our last blog, we are focusing on the near-to-surface weak layers of the snowpack. Most treacherous of these are thin layers of faceted crystals right next to thin melt-freeze crusts which formed in the most recent, highly variable weather phases (compare to our graph,
“crust-sandwich”.
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| Snowpack analysis in the Tux Alps. In background, a remotely-triggered slab avalanche on 17.03.2021 (photo: 18.03.2021) |
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| Profile from the avalanche fracture in the above photo. “crust sandwich” East, 2140m, 40° |
Naturally triggered slab avalanches, presumably fractured near these layers, have been observed over recent days in E-S-W aspects at altitudes between 2500 and 2800 m.
In addition, for a short time there are also loosely-packed layers of fresh snow blanketed by snowdrifts (esp. at high altitudes, increasingly frequent on shady slopes) which include thick layers of graupel.
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| Graupel frequently accompanied the recent bouts of snowfall. (photo; 18.03.2021) |
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| Decomposed crystals as a weak layer between crusts. These were recently responsible for settling noises, now they require special caution above 2500 m in particular. 2350m, North; Ötztal Alps |
Southern East Tirol: more favourable
In central East Tirol and in southern East Tirol there was comparatively little precipitation. There, small, far more easily recognizable snowdrift accumulations (compared to northern regions) require caution.
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A backcountry tour on Bergerkogel in central East Tirol. Less fresh snow, shallower snowdrifts.
(photo: 16.03.2021) |
Powder snow
No doubt about it: the fresh snow is mighty tempting. A short-lived pleasure, dependent on radiation. And it doesn’t even need to be steep….
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| Joys of powder in the Tux Alps (photo: 18.03.2021)
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