Outlook
Wedged between a high over southern Scandinavia and a low over Russia, Tirol will be pressed into a powerful northeasterly airstream tomorrow, Friday 22.02. Strong to storm-strength winds in the mountains will be the result, along with some precipitation, particularly in the eastern regions.
The fresh snow and, in some places, loosely-packed old snow will be transported by strong winds. New snowdrift accumulations will form, particularly in gullies, bowls and areas adjacent to ridgelines. The drifted masses will be deposited on top of a rather loosely-bonded old snowpack surface on shady slopes, consisting of decomposed and faceted snow crystals and, in some places near ridgelines, surface hoar (Nigg effect), thus will be triggerable even by minimum additional loading in places.
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| The snowpack surface on shady slopes often consists of settled, slightly metamorphosed (faceted) powder, so-called burled powder. This snow can briefly form a weak layer for the snowdrifts deposited on top of it. (photo: 21.02.2019) |
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| In foreground, surface hoar is visible on shady slopes near ridgelines (Nigg effect). Strong northerly winds will presumably transport it, so that it will seldom persist as a weak layer. Gilfert in the Tux Alps (photo: 21.02.2019) |
In high alpine regions, particularly along the Main Alpine Ridge, avalanche prone locations occur more frequently, particularly in the eastern regions where recent snowfall has been heaviest. Freshly generated snowdrift accumulations in shady terrain and, increasingly, in very steep areas adjacent to ridgelines in all aspects can be triggered. Avalanche danger is increasing over widespread areas, it will reach danger level 3 (considerable) in the Zillertal Alps, Venediger Massif and Glockner Massif.
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| Fresh snow and strong winds will create heightened avalanche danger widespread. |
Glide-snow avalanches remain an enduring threat this winter. They can grow to large size, in isolated cases even to very large size, particularly in the regions where snowfall has been heaviest. Thus, they need to be taken into consideration in all backcountry tour planning.
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| A popular ascent to the Kellerjoch in the Tux Alps. Many backcountry skiers seem to be unaware of the lurking dangers of glide-snow avalanches.... (photo: 21.02.2019) |
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| Even taking a break at a high alpine pasture hut can have unpleasant consequences. (photo: 21.02.2019) |
In East Tirol, avalanches can be triggered in the weak old-snow fundament from place to place and grow to medium size. The most delicate spots are north-facing slopes at 2000-2600 m. Avalanche prone locations occur seldom and are ordinarily not recognizable by backcountry skiers. Areas where the snow is shallow, e.g. transitions from deep to shallow snow, are where avalanches love to trigger.
Over the weekend, weather conditions will improve. The high pressure system over Scandinavia will spread out in our direction. According to ZAMG weather forecasts, a tranquil and unseasonably mild weekend awaits us, with dry air and lots of sunshine.
Review
The inordinately warm temperatures which have reigned since the beginning of last week have had an enormous effect on the snowpack, especially on sunny slopes and at low altitudes in general.
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| The graph shows the maximum, minimum, average (gray line) and current snow depths (magenta) at our observation station in Obertilliach. We are now just below the average. |
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| The chamoix are delighted when the snow recedes and temperatures rise. Nockspitze. Northern Stubai Alps (19.02.2019). |
Due to the snowpack becoming thoroughly wet to an increasing extent, together with the augmented penetration of water down to the ground, glide-snow avalanches continue to be observed. In isolated cases, they have also buried exposed roads. On the other hand, the frequency of wet loose-snow avalanches in extremely steep terrain has decreased.
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| An alm hut on the Rosskogel (Stubai Alps) pushes back against the gliding snow masses. (photo: 19.02.2019). |
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| In Seduk near Neustift in Stubaital, the deposits of a glide-snow avalanche press into the vicinity of houses. (photo: 20.02.2019). |
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| A glide-snow avalanche which released in the wee hours of Thursday (21.02) buried the Planseestrasse near Breitenwang (Reutte district) along a length of approximately 20 meters. (photo: 21.02.2019). |
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| A “glide-snow family” (l to r): a glide crack, next to it a fresh glide-snow avalanche (snow in the fracture area is still visible), next to that an older glide-snow avalanche, where the snow which came to rest has already melted, and next to that, yet another glide-snow avalanche which released before this one. (photo: 21.02.2019). |
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| The plummet path of a glide-snow avalanche on the Bschlaber state road. (photo: 18.02.2019). |
Seen from the vantage point of a skier or freerider, the conditions over the last few days couldn’t have been better. The sunny, warm and windless days provided the best backcountry touring conditions imaginable. Avalanche danger in all of Tirol was low, apart from the risks of glide-snow avalanches.
In spite of above-average temperatures for this juncture of the season, shady slopes still had terrific powder to offer. The snowpack where it was not exposed to the sun enjoyed unimpaired outgoing radiation at night, so did not suffer in the slightest from the higher temperatures. The strong outgoing (longwave) radiation also brought about transformation of the fresh snow and drifts from Monday, 11.02, thereby making it unbonded. The essential “slab” for a slab avalanche, was thus no longer available. Seen from a skier’s point of view, the snow forfeited only very little of its quality.
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| Cloudless blue skies and the finest burled powder in Schmirntal (photo: 21.02.2019). |
Slopes exposed to sunshine, on the other hand, during the night were not able to relinquish the warmth which solar radiation poured into them during the daytime. The snowpack became increasingly moist. Following several cycles of re-freezing over the last few days, the first corn snow could be savored on steep, south-facing slopes. On east and west-facing slopes the sun was generally not strong enough to form a melt-freeze crust capable of bearing loads. The result: breakable crusts.
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| On steep south-facing slopes, corn snow was just waiting to be enjoyed. Nockspitze, Stubai Alps (photo: 19.02.2019). |
