Expect changing weather on Tuesday: high freezing levels dropping over the day, intense rain switching to snow, and strong winds. Warming will weaken the snow and new snow will form fresh slabs. Be very cautious with these rapid changes.
Confidence
Moderate - Timing, track, or intensity of incoming weather system is uncertain
Weather Forecast
TUESDAY: Cloudy with rain switching to snow, accumulation 20 cm, strong to extreme southwest winds, alpine temperature 0 C dropping to -5 C, freezing level 2600 m dropping to 1300 m over the day.WEDNESDAY: Cloudy with snowfall, accumulation 15 cm, light to moderate south winds, alpine temperature -5 C, freezing level 1300 m.THURSDAY: A mix of sun and cloud, light southwest winds, alpine temperature -6 C, freezing level 1300 m.
Avalanche Summary
On Sunday, storm slab and loose wet avalanches were widespread across the region. They were small to large (size 1 to 2), on all aspects, and at all elevations. They were triggered naturally, by skiers, and by explosives. Cornices were also reactive, which triggered storm slabs on the slopes below.
Snowpack Summary
Warm temperatures have moistened the snow surface on all aspects and at all elevations. The forecasted snow on Tuesday will fall on this. 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, and/or a melt-freeze crust from late March is now buried about 60 to 120 cm. This layer is spotty in its distribution but has recently produced large avalanches. It is mostly likely to be problematic on west, north, and east 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.