A sunny weekend awaits us. Caution towards wet-snow avalanches during course of day!
Following a typical variable period of April weather bringing us rainfall regionally up to 2000m in many northern regions, today on 22.04 weather conditions are now improving. During the night, skies will begin to clear. On Friday and Saturday, sunny and warm days are promised ahead. On Sunday, 25.04, convective cloud build-up could bring a bit of precipitation.
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| Last week was cold and variable. View from the Tux Alps towards the Karwendel (photo: 22.04.2021) |
Caution: daytime increase in avalanche danger
Warm temperatures and intensive solar radiation will weaken the snowpack to an increasing degree over the next few days. Sunny and shady slopes need to be examined separately.
Sunny slopes
On sunny slopes the near-surface layers (deposits from 05.04.2021) are forfeiting their firmness. These weak layers are found esp. above the recently formed melt-freeze crusts. Water seepage due to the melting process can lead to a raised proneness to triggering of the snowpack, including naturally triggered avalanches. Also possible: triggering of slab avalanches through the impulse of a wet loose-snow avalanche in extremely steep terrain.
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| Naturally triggered slab avalanche on 21.04, afternoon, on a south-facing slope at about 2500m in the Stubai Alps. A wet loose-snow avalanche was the possible triggerer. The slab fractures on a melt-freeze crust which formed starting on 12.04, on which dust from the Sahara desert was deposited on 12 April. (photo: 21.04.2021) |
High-alpine sunny slopes are also hit by this.
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| A slab triggered remotely at 3000 m on a south-facing slope in Granatspitz Massif (photo: 21.04.2021) |
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| Also needful of attentiveness: isolated glide-snow avalanches on steep, smooth ground (mostly glide-snow avalanches released during the intensive phase of warmth at the end of February or end of March). Stubai Alps, 20.04.2021 |
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| A typical sunny-slope profile at high altitude. Above a thick melt-freeze crust which formed starting on 3 April, a sequence of thin crusts and weak layers resulting from water seepage. 2130m, west, Tux Alps, 21.04.2021 |
North-facing slopes
North-facing slopes were moistened deeply up to 2400m in North Tirol, up to 2000m in East Tirol, this winter. This occurred on 2 April when it rained. Numerous naturally triggered avalanches, increasingly frequent as wet loose-snow avalanches, also as slab avalanches, were the result. With today’s rain input (22.04.2021) and the huge diffuse radiation at the beginning of the day, the snowpack in the northern regions was again moistened, at least superficially.
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| Precipiation on 22.04.2021 up to 19:00 Uhr |
Temperature reserves hardly exist anymore. Warmth and diffuse radiation can thus lead to deeply penetrating water seepage. This will weaken the snowpack, making the snowpack easier to disturb by winter sports enthusiasts, but also leading to increased naturally triggered avalanches.
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| Snow profile NE 2335m shows a rather flat temperature progression (doubtless flattened further today, 22.04). Noteworthy: the ground-level, slightly encrusted layer. Particularly in spots where snow was shallow at this altitude, we can assume a thoroughly wet snowpack as of Saturday late afternoon. The results could be slab avalanches which fracture at ground level. |
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| On shady slopes, superficial loosely-packed snow avalanches currently, also below 2400 m; also slab avalanches possible in the course of the day. (photo: 21.04.2021) |
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| Snowpack, a snowpack simulation model used by us, shows that the snow cover over the next few days on north-facing slopes will become thoroughly wet down to ground level: pink dots below right below in the left depiction. Right: simulated profile on Gallreideschrofen in Gschnitztal: superficially, melt-freeze crusts dominate; at ground level, expansively metamorphosed layers. |
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| Overview of simulated “avalanche activity indices” for today, 22.04.2021, 3:00 pm. “1” denotes increasing weakness. |
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| For comparison: forecast for Saturday, 24.04, 3:00 pm |
Equally noteworthy: in the Zillertal Alps along the Main Alpine Ridge, naturally triggered avalanches were registered in extremely steep north-facing slopes at 3000m. Moment of release is not yet certain, probably very recently. The fractures were apparently rather large. This needs to be coordinated with other observations, since other winter sports enthusiasts also reported on high-altitude, wind-protected zones.
In early morning, mostly favourable conditions. Caution: danger of falling.
As clear nights freeze the near-surface layers of the snowpack, we assume a melt-freeze crust capable of bearing loads on sunny slopes below 2200m in the early morning hours, at least at high altitudes. Caution: in steep terrain there is a huge danger of falling. Melt-freeze spikes and climbing spikes ought to be part of every rucksack’s equipment.
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Conclusion: plan your time carefully.
In the coming days, careful tour planning, especially good time planning, is highly important. Avalanches can release increasingly easily over the course of the day as the snowpack becomes moister - whether triggered by skiers or triggering naturally. Particular caution is required on shady slopes below 2400m, where slab avalanches can fracture increasingly at ground level. In this connection, southern East Tirol has a far better situation, where the snowpack fundament is compact.
IF you plan your time carefully, you will be rewarded by fantastic firn snow.
