Winter sports enthusiasts, beware! At high altitudes avalanches easily triggered in some regions.

 Cold front bringing snow

After an initially warm, then variable November it is snowing down to low altitudes in widespread parts of Tirol. The snowfall will be heaviest today (22.11), tomorrow it is expected to taper off everywhere. According to ZAMG Weather Service the main regions of precipitation lie in the Tux and Zillertal Alps, and the northern and southern parts of East Tirol, where up to 40 cm of fresh snow is expected at high altitudes. Southern Ötztal and Stubai Alps should get up to 30 cm, elsewhere 20 cm is anticipated generally.

48-hr fresh snow forecast. Main areas of precipitation lie in the southeastern regions.

Southerly winds shifted to westerly/northwesterly, blowing mostly at moderate strength. They will intensify significantly at high altitudes over the coming days. Main wind direction will remain W/NW.

Wind forecast for Wednesday, 23.11. 8:00 pm

Considerable avalanche danger at high altitudes

The combination of snowfall, wind and the current snow layering is causing a significant increase in avalanche danger. At high altitudes, where the cohesive area-wide snowpack has persisted, we assume that avalanche danger will be considerable.  Wherever snowfall is heaviest are the least favorable regions of all. Danger increases with ascending altitude. Shady slopes tend to be at greater risk. Sunny slopes need to be evaluated critically, particularly near ridge lines and in high alpine terrain in general.

A glance back: variable weather conditions, recurrent precipitation, sometimes as rain

The snowpack

The snowpack is a reflection of the sequence of weather conditions. Appropriately, we find a series of crusts and soft layers, the latter frequently composed of loose, faceted crystals, even depth hoar in some places. This constitutes a serious weak layer for the mass of fresh snow which lies on top of it (impacted by wind). The additional load of one single winter sports enthusiast can be enough to disturb the weak layer and trigger the release of a slab.

Snow profile, Gurgl Massif, 19.11.2022. 3065m, NW, 34° Potential weak layers near the surface.

Snow profile in Weisskugel Massif, 21.11.2022. 3050m, SE, 33°.  There is at least one potential weak layer for slab avalanches even in sunny terrain at high altitudes.

Web camera photos are extremely helpful in determining whether there was a cohesive area-wide snowpack prior to the current snowfall. Here are photos of where that was the case. More details at foto-webcam.eu.   

View into Tux Valley, a region that has already had much snow. Photo from 15.11.2022

High alpine terrain above 2800m in the Weisskugel Massif

Northern East Tirol. South-facing slopes were bare of snow up to high altitude.

In the Lienz Dolomites and on the Carnic Ridge there was snow on the ground prior to the current snowfall. Our photos reveal it was encrusted on the surface, often loose below the crust.

A plea

In many places there is at least one ugly and threatening weak layer at high altitudes, on top of which is then a well-bonded mass of (fresh) snow. Thus: ideal prerequisites for a slab release. Due to the shallow covering of the weak layer, it can be triggered with relative ease by winter sports enthusiasts. Therefore: be careful, attentive and restrained in the mountains!

By the way, for a brief spell we are going to observe increasingly frequent glide-snow slides on grassy slopes in the regions where snowfall is heavy. In addition, loose-snow avalanches are expected in extremely steep terrain.

Beware snowdrifts in high alpine terrain. Also loose-snow and glide-snow slides.

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

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.

The next blog will be published whenever a significant change in the snow or avalanche situation occurs.