Avalanche
Avalanche danger across broad swaths of the Alps and Pyrenees is expected to spike to dangerous levels on Sunday, December 11, as fresh snowfall and storm conditions combine to leave snowpacks unstable and prone to sliding.
Forecasters and national avalanche services across France, Switzerland, Austria, Italy, and Spain are urging extreme caution for anyone planning to ski, ride, or travel in mountain terrain on Sunday. Sunday will be the first sunny day after multiple days of snowfall that saw up to 1.5 meters (5 feet) of snowfall across the western Alps. Multiple regional agencies have highlighted that heavy snow and wind loading have created dangerous avalanche conditions, particularly off-piste and at higher elevations, where risk levels are forecast at 4 (“high”) and even 5 (“extreme”) on the European avalanche danger scale.
Two main weather factors are driving the heightened danger:
- Heavy recent snowfall: In parts of the Alps and Pyrenees, ski areas and mountain forecasters report that large amounts of snow have fallen in just a few days, building deep new layers on top of older, weaker snowpacks. This creates prime conditions for wind slabs and slab avalanches on steep terrain.
- Wind and storm impact: Gusty winds accompanying the snowfall have redistributed snow across ridges and slopes, contributing to areas of unstable loading that can easily be triggered by a skier or natural release.
Collectively, these factors mean that avalanche danger this weekend will be significant across many classic backcountry zones and steep alpine terrain, especially above the tree-line. Even well-traveled lines that normally hold firm can be unpredictably unstable right now.
Meteo France issued a special avalanche bulletin on January 10, warning of highly unstable snowcover in the French Alps and Pyrenees. According to the bulletin, conditions are so fragile that even a single skier can easily trigger large avalanches. In France, the following massifs are concerned:
- Chablais,
- Aravis,
- Mont-Blanc,
- Beaufortain,
- Haute-Tarentaise,
- Vanoise,
- Haute-Maurienne,
- Maurienne,
- Grandes-Rousses,
- Oisans,
- Thabor,
- Pelvoux,
- Champsaur,
- Queyras,
- Embrunais-Parpaillon,
- Devoluy,
- Ubaye,
- and Haut-Verdon (without Haut-Var).
One meter of snow has fallen since Thursday, December 8, accompanied by strong winds. Recent snowfall is resting on particularly fragile layers of snow, resulting in considerable instability of the snowpack and making large-scale avalanches very likely. Mountain users are urged to exercise extreme restraint and avoid unmarked runs.
Likewise, the Swiss Avalanche service SLF has advised that avalanche danger in many regions has been raised to Level 4 (“high”). “Large quantities of fresh snow and the wind-drifted snow of the last four days are poorly bonded with the old snowpack in many places,” SLF warned in today’s bulletin. “More natural avalanches are possible until late in the night, even large ones. Avalanches can in many places be released, even by a single winter sport participant and reach dangerously large size. Whumpfing sounds and the formation of shooting cracks when stepping on the snowpack serve as an alarm indicating the danger. Remotely triggered avalanches are possible. Backcountry touring and other off-piste activities call for extensive experience and great restraint. The danger exists primarily in alpine snow sports terrain. Avalanches capable of reaching valley bottoms and endangering exposed transportation routes are unlikely to occur.”
In Switzerland, regions with high risk levels are:
- northern Alpine ridge from Les Diablerets to the Aletsch region,
- extreme west of Lower Valais
- remaining northern flank of the Alps from the Vaud Alps to the Glarus Alps (without the Prealps and southern Valais)
- Val Ferret,
- and the Mattertal.
Resorts and official avalanche services generally maintain controlled piste areas, but off-piste terrain and unpatrolled slopes remain particularly hazardous. In these conditions, carrying avalanche safety gear (transceiver, probe, shovel), traveling with experienced partners, and consulting official avalanche bulletins before heading into the mountains are essential precautions.
Avalanche agencies across Europe are stressing that conditions on Sunday, December 11, will be extremely treacherous and are urging for people to be careful and vigilant.
