Freezing levels will rise over Monday along with sunny patches in the afternoon. The warming will weaken the snow and increase the likelihood of triggering slabs, cornices, and loose wet avalanches. Expect the hazard to rise over the day.
Weather Forecast
MONDAY: Cloudy with light morning snow and afternoon clearing, accumulation 2 to 5 cm, light southwesterly winds, alpine temperature -4 C, freezing level 1500 m rising to 2000 m by late afternoon.TUESDAY: A mix of sun and cloud early morning then mostly cloudy with rain switching to snow at higher elevations, accumulation 10 mm, moderate to strong southerly winds, alpine temperature 0 C, freezing level 2600 m dropping to 1700 m over the day.WEDNESDAY: Mostly cloudy with light snowfall, light southeasterly winds, alpine temperature -4 C, freezing level 1500 m.
Avalanche Summary
On Saturday, ski cuts and explosives triggered many cornices and storm slabs. Cornices were generally small (size 1.5), but they triggered slabs on slopes below. The storm slabs were also generally small (size 1 to 1.5), 10 to 20 cm thick. Loose wet avalanches were observed below about 1900 m.
Snowpack Summary
Around 30 cm of recent snow and strong southerly winds have created new slabs at higher elevations. This snow overlies a melt-freeze crust. On ridges, cornices are reported to be large and fragile. At lower elevations, recent precipitation fell as rain, so expect moist or wet snow conditions.A weak layer consisting of surface hoar, facets, or a sun crust from late March is now buried about 60 to 90 cm. This layer is spotty in its distribution but has recently produced large avalanches. It is mostly likely to be problematic on shady aspects between 1900 m and 2250 m.Below this, the snowpack is well-settled and strong.
Problems
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.
Persistent Slabs
Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.
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.