Forecast sunshine and warming will increase the likelihood of triggering in a wide range of avalanche problems on Thursday. Expect stability to deteriorate over the day.
Weather Forecast
Thursday: Mainly sunny with cloud increasing over the day. Moderate south winds. Freezing level rising to 2000 metres with alpine high temperatures around -2. Weak overnight cooling.Friday: Cloudy with isolated flurries and a trace of new snow, increasing overnight. Moderate south winds. Freezing level to 1900 metres with alpine high temperatures around -3.Saturday: Cloudy with continuing flurries bringing 5-10 cm of new snow. Light to moderate southwest winds. Freezing level to 1700 metres with alpine high temperatures around -4.
Avalanche Summary
Reports from Tuesday included observations of several large (size 2) wind slabs that released naturally as a result of recent strong winds.Observations were hindered by poor visibility on Monday.Reports from Sunday and late last week showed a pattern of heightened cornice failure activity, with several cornice releases triggering large persistent slabs and wind slabs.Looking forward, a trend toward clearing skies and warming temperatures will be increasing chances of loose wet avalanche activity as well as testing the strength of storm slabs and wind slabs formed in the wake of recent snowfall and wind events.
Snowpack Summary
About 50 cm of recent storm snow covers a supportive crust on all aspects to at least 2100 m (and possibly higher on south aspects). Shifting strong southwest and north winds pressed and redistributed the most recent accumulations into new wind slabs on a range of aspects on Monday.Within the upper snowpack there are now several different crusts with the shallowest of these (down about 25 cm) remaining a concern as the uppermost layer of storm snow settles and bonds to it.There is some lingering concern around the mid-March persistent weak Layer in the alpine where it is found 100 to 150 cm below the surface. This buried crust/surface hoar interface is still capable of producing large avalanches if it is triggered (think step-down from a surface avalanche or a cornice collapse).Deeper persistent weak layers from December and January may be starting to become reactive to very large triggers. A recent cornice collapse is believe to have initiated a slab release on an early season layer, 300 cm deep.
Problems
Loose Wet
Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.
Cornices
Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.