Cold front brings snowfall, most in northern Zillertal Alps
Over the last 24 hours there has been precipitation throughout Tirol, above approximately 1200 m as snowfall. Maximum precipitation was registered in the northern Zillertal Alps: as much as 40 mm from place to place. Widespread 10-20 mm was registered. This corresponds to approximately 10-20 cm of fresh snow. In the heights there were frequently strong winds blowing, initially southerly, then northerly.
 |
| Increase in fresh snow delivered by the cold on 04.11.2022 |
 |
| A similar picture in this 24-hr overall snowfall map (04.11 - 05.11) by Hydro Online |
 |
| Northern Zillertal Alps before the cold front arrived |
 |
| Northern Zillertal Alps after the cold front arrived. A brief foretaste of winter... |
Effects of snowfall on avalanche danger
One potential avalanche danger can be observed widespread in the regions with the most recent snowfall. It stems from freshly generated snowdrift accumulations in shady, very steep terrain, namely above about 2800 m. The snowdrifts were deposited frequently on a weak surface layer of faceted crystals from October. Currently, small-to-medium sized slab avalanches can be expected. These releases can be triggered by the weight of a winter sports enthusiast in isolated cases. Increasingly frequently, it is likeliest to occur near ridge lines and behind steep protuberances in the terrain. Current weather forecasts foresee improving weather conditions and rising temperatures, so the fresh snow will settle rapidly and the danger will swiftly recede.
In addition this weekend, increasingly frequent small loose-snow slides can be expected in extremely steep terrain; as well as small slides of glide-snow on steep grass-covered slopes.
Review
Weather
According to ZAMG Weather Service, we have just lived through the warmest October in the history of weather measurement. Their measurements go back to the year 1853.
 |
| October 2022 was unbelievably warm... |
 |
| A glance back to the beginning of October: a sunny, extraordinarily warm and precipitation-free month. Often at high altitudes the precipitation was registered in the form of rain. At the present moment we see a drop in temperature from the cold front including snowfall and shifting winds. |
Snowpack
Before the cold front arrived on 4 November on shady slopes there was a more or less cohesive, area-wide snowpack above approximately 2800 m, on south-facing slopes only in high alpine glaciated terrain. Currently we don’t know much about the condition of the old snowpack, but assume that a melt-freeze crust has frequently formed on the surface. In sunny high alpine terrain that crust will be capable of bearing loads, in shady terrain it will be breakable. On shady slopes we expect to find a loose layer of faceted crystals from October beneath this shallow crust. That layer is currently the only significant weak layer we perceive which could unleash slab avalanches.
 |
| Snow profile from 16 October 2022, 3170m, NE, 20° on Daunferner glacier in the central Stubai Alps. The arrow points to a potential weak layer beneath a thin crust. (c) Lukas Ruetz |
.jpg "Blick vom Kaunertaler Gletscher Richtung Süden. Ausgangssituation vom 03.11.. Eine mehr oder weniger zusammenhängende Schneedecke gibt es nur in großen Höhen, vermehrt im schattigen Gelände.") |
| View from Kaunertal Glacier towards the south. This was our point of departure on 3 November. A more or less cohesive area-wide snowpack existed only at high altitudes, particularly in shady terrain. |
