Lots of fresh snow in the mountains
A cold front moving swiftly across Tirol is bringing heavy precipitation to the southeastern regions of the land. ZAMG Weather Service anticipates 50-80 mm of precipitation between Monday (26.10.2020) at 6:00 pm and Tuesday (27.10.2020) at 9:00 am. As temperatures rapidly drop, the snowfall level on the Main Alpine Ridge will descend from 2200 m down to 1300 m in the latter part of the night. Further south the temperatures will not drop as quickly. The snowfall level there is expected to be at about 1500 m, according to ZAMG.
 |
| Overview of precipitation by 9:00 pm today, whose focus will shift southeast during the night. |
 |
| Heavy precipitation in Obernberg (Brenner). Lower temperatures from the cold front are also visible. |
 |
| Initial snowfall in the mountains, winds strong-but-easing, temperatures dropping (weather station Eissee on Stubai Glacier). |
Between 50 and 100 cm of fresh snow is expected in the mountains along the Main Alpine Ridge from Ötztal Alps eastwards and in East Tirol.
 |
| Fresh snow forecast over 24 hrs: purple zone indicates 75-100 cm. |
Avalanche danger consequences
Naturally triggered slab avalanches briefly possible
Heavy snowfall leads to a correspondingly larger load on the snowpack. In high alpine regions (above 3000m) we expect that naturally triggered avalanches will unleash as a result of this additional load, particularly on north-facing slopes, some of which will be large-sized slab avalanches. This is a direct consequence of the weak layer inside the old snowpack (discussed at length in the last Blog). As precipitation slackens off and winds ease, the likelihood of naturally triggered slab avalanches will then rapidly decrease.
By the end of this bout of snowfall, winter sports enthusiasts will probably be able to trigger this weak layer only by large additional loading and then, particularly in very steep transitions from shallow to deep snow. Nevertheless, caution is urged towards fresh snowdrift accumulations which have frequently been deposited on top of a weak layer (consisting of loosely-packed powder). Such danger spots are found more often near ridgelines at high altitudes and in lee areas behind protruberances in the terrain.
Over grass-covered slopes: snow glides
Wherever there are large amounts of snow on steep, grassy slopes, an additional danger needs to be taken into consideration: glide-snow slides and glide-snow avalanches. Caution is urged especially on hikes at the foot of steep hillsides. In our experience, due to the warm ground many such avalanches are unleashed at this juncture of the season. For examples, see the blog from 13.10.2020: photos of Gleitschneelawinen.
Loose-snow avalanches from rocky terrain
Loose-snow slides or avalanches are another consequence of fresh snowfall at this juncture of the season. Since solar radiation is still quite strong, the snowpack tends to become moist after the snowfall, and thereby forfeits its firmness. In sunny, rocky terrain, avalanches subsequently release more frequently from point to point wherever snowfall has been heaviest.
The upshot
Over the next few days winter sports enthusiasts who venture into outlying terrain need to have enough grasp of avalanche science to assess the risks on-site. Moreover, greater caution is called for, i.e. defensive conduct for a short time.
Our next blog will be published whenever there is a significant change in snow and avalanche conditions.
