Heavy snowfall, gale-strength winds: dangerous avalanche situation!

Current situation & outlook

A powerful westerly/northwesterly airstream is currently thrusting a series of cold and warm fronts towards the Alps. By Saturday morning, 16.03, we can expect heavy precipitation, according to ZAMG weather forecasts. In the mountains, 50-100 cm of fresh snow is anticipated. Winds will be blowing at strong to storm strength, even reaching gale strength in some places tomorrow, Friday 15.03.

By Saturday morning (16.03) 60-100 cm of fresh snow is expected along the Vorarlberg border, 30-50 cm widespread in the remaining regions of North Tirol and Hohe Tauern.

Gale-strength winds are leading to wide-ranging snow transport of the fresh snow in some places.

 Deep-winter conditions on the Arlberg expressway after the perturbance arrived on Thursday afternoon. (photo: 14.03.2019).

The huge amounts of fresh snow, combined with strong winds, are ratcheting up avalanche danger levels. These will reach level 4, high, in the major areas of precipitation in the western regions of North Tirol. Elsewhere, considerable avalanche danger can be expected over widespread areas above 1800 m, and this rank lies at the uppermost border of the danger scale for level 3.

Potential weak layers for slab avalanches are currently found primarily in the uppermost section of the snowpack (excluding in southern East Tirol):

• The highly variable conditions and warmth, including solar radiation, of the last few weeks has led to the forming of numerous melt-freeze crusts, beneath which faceted snow crystals were generated. Snowpack analysis demonstrated no striking tendency to fracture propagation there, nevertheless fractures, at very least in the areas where snowfall has been heaviest, cannot be ruled out. We currently focus the threat on an altitude band between 2400 m and 2800 m in NE/ E aspacts. 

• The snow from Wednesday night, 13-14.03, cold, loosely-bonded fresh snow above 2200 m in wind-protected terrain, can potentially form a weak layer. 

• In addition, the current batch of fresh snow is also a potential weak layer for slab avalanches, since it was loosely deposited in wind-protected terrain and subsequently covered by snowdrifts.

During the variable weather of the last few weeks, numerous melt-freeze crusts were able to form, under which loose, faceted snow crystals are found in places.  (photo: 13.03.2019).

On Wednesday night, 13.03, there was snowfall, bringing a few centimeters of fresh snow over widespread areas at low temperatures. This fresh snow is a potential weak layer for slab avalanches.

Fresh snow and snowdrifts have been deposited atop a weak old-snowpack surface from region to region and can be triggered in all aspects above about 2200 m. The snowdrift accumulations are quite deep.

During the intensive periods of precipitation we expect numerous naturally triggered avalanches. Due to the sizeable amounts of fresh snow, the avalanches can be expected to reach large size. The higher temperatures resulting from the warm front on Friday, 15.03, will also bring about better bonding of the uppermost layers of the snowpack. Thereby, fractures can more easily be propagated. In addition, avalanche activity is expected to increase right at this juncture in time.

On Friday morning, 15.03, snowfall will presumably reach its climax. Simultaneously, temperatures will rise, and the snowfall level will ascend. We can then expect the culmination of naturally triggered avalanche activity.

An ascent of the snowfall level also means that increasing amounts of rain will penetrate the snowpack below 2000 m. Where this is heavy, the likelihood of loose-snow avalanches triggering on extremely steep slopes will increase. In addition, due to the rain impact and also due to the greater weight of the fresh snow on top of the snowpack, increasingly frequent gliding snow activity can also be expected, particularly on steep, grass-covered slopes below 2600 m, and especially below 2200 m.

In East Tirol there is a strong gradient from north to south with regard to the precipitation which is forecast. In the Hohe Tauern the snowfall will be heavy, bringing up to 70 cm. Further towards the south, the amount of fresh snow will swiftly decrease; south of the Drau, only a few centimeters are anticipated. Accordingly, avalanche danger levels are not expected to change significantly there. Danger is ranked as moderate in the Defereggen Alps, Schober Massif and Lienz Dolomites above 1800 m. The danger of generally small-sized snowdrift accumulations which can trigger primarily on shady, very steep, ridgeline slopes is also a threat.

Following the end of this period of precipitation on early Saturday morning, 16.03, weather conditions are expected to improve swiftly. The weekend promises lots of sunshine and warmth, according to ZAMG forecasts. The zero-degree level will ascend to 3000 m. The great amounts of fresh snow will rapidly become moist up to intermediate altitudes on sunny slopes. Numerous moist-snow and wet-snow avalanches can be expected on very steep slopes. Solar radiation and daytime warmth will also bring about better bonding of the snow masses, thereby leading to a short-term increase in the likelihood of slab avalanches triggering. Snowdrift accumulations will remain prone to triggering on shady slopes more than anywhere else.

On the coming weekend, it is important to ski defensively. The first day of good weather following a period of intensive snowfall and storm wind is particularly prone to accidents, as everyone knows.

Saturday, 16.03, and Sunday, 17.03, promise warm and dry weather. On Monday, 18.03, a cold front will arrive, bringing precipitation again. (©Meteoblue).

Review
Conditions were highly variable last week. Particularly Monday, 11.03, and Tuesday, 12.03, there was heavy snowfall (see  blog of 12.03.)). In the following days the weather was more pleasant, but strong westerly winds refused to slacken off. As a result, fresh snowdrift accumulations formed ever anew, particularly on shady slopes.

Variable weather with fresh snow, lots of wind and fluctuating temperatures. Falkaunsalpe weather station, N. Ötztal Alps.

As a result of the first solar radiation following the intensive snowfall of Monday night, 11.03, numerous loosely-bonded avalanches released in extremely steep, sunny, rocky terrain. Northern Massif.  (photo: 13.03.2019).

Fresh snowdrift accumulations were triggered as slab avalanches primarily on shady slopes. Stubai Glacier (12.03.2019).

During recent days, westerly winds were blowing predominantly at strong velocity in the Grieskogel Massif. (photo: 12.03.2019).

The fresh snow is clearly still powdery. This is visible in the snow cloud which the skier stirs up, and also in the snow plumes in the background. Gaiskogel, Stubai Alps  (photo: 13.03.2019).