All signs point to Danger Pattern 4 (cold on warm) at high altitudes

Following snowfall, trigger-sensitive weak layer highly probable due to dp.4

Weak layer caused by dp.4 (cold on warm)

In our last Blog we referred to the “small snowdrift problem at high altitudes” and the possible development of Danger pattern “cold on warm” (dp.4). Back then on 07.04 we had no information about the development of a malicious weak layer. In the interim reports keep coming in about slab avalanches in a superficial weak layer due to Danger Pattern dp.4.

Based on current information we can narrow down the problem zones due to dp.4 to the following:

• Regions where recent snow was heavy, particularly Silvretta, Arlberg region, Karwendel, regions along the Main Alpine Ridge and northern East Tirol
• Shady slopes between 2600 and 2800m
• Sunny slopes above 2800m, even more above 3000m

On the monthly graph from the Pitztal Glacier station we recognize not only the start of precipitation on 31.03 but also the temperature leaps which followed, including brief period of high wind impact.

Weak layer due to dp.9 (covered graupel)

Just as conceivable, however, are massive deposits of graupel which were blanketed by the recently generated snowdrift accumulations in all aspects. Graupel precipitation was repeatedly observed during the last round of precipitation. Similar to dp.4, we assume that problem zones are evident above about 2600m.

Some reports about avalanches

Avalanche releases were reported from Wildebene and Albonakopf in the Arlberg region, from Felderkogel in the Ötztal Alps, from Grossglockner in the Glockner Massif and from Grosser Geiger (SW, 3200m) in the Venedig Massif. In addition, a report came in today (11.04) about large-scale settling noises in the Venedig Massif above 3000 m.

With a webcam from  Lucknerhaus the recent naturally triggered slab avalanches are recognisable. The lower avalanche triggered today, 11.04, at midday.  (c) foto-webcam.eu

Avalanche Felderkogel. The release was remotely triggered. N, 2700-2750m (photo: 10.04.2022)

Heightened caution during the next few days

As a result of expected higher temperatures and solar radiation, the snowpack will be briefly weakened and the likelihood of slab avalanches triggering will be heightened. We assume that the weak layer will no longer be a threat once it has become thoroughly wet. Thus, the problem will last a little longer on shady slopes. This depends on coming weather developments, including diffuse radiation, and cannot as yet be pinned down to a certain length of time. Winter sports enthusiasts with lots of experience in evaluating avalanche dangers on-site can easily recognize a potential problem through snowpack analysis and stability tests, and react accordingly. Of course we are grateful for your reports, at lawine@tirol.gv.at