Forecast warm temperatures and potential extended sunny periods on Thursday and Friday will keep the avalanche danger elevated
Confidence
Moderate - Timing or intensity of solar radiation is uncertain on Thursday
Weather Forecast
THURSDAY: Cloudy with sunny periods / Light to moderate northwest wind / Alpine temperature -3 / Freezing level 1500mFRIDAY: Cloudy with sunny periods / Moderate southwest wind / Alpine temperature -2 / Freezing level 1300mSATURDAY: Flurries / Light southwest wind / Alpine temperature -2 / Freezing level 1300m
Avalanche Summary
A report from Tuesday indicated a natural size 2 cornice failure that was suspected to be triggered by warming temperatures at tree line on a west aspect. Additionally, on Tuesday and Wednesday several explosive and skier controlled avalanches to size 2 and 2.5 were reported from a variety of aspects. These were mostly wind and storm slabs failing 10-40cm deep. Some were also triggered by cornices pulling out 20-40cm slabs on slopes below.
Snowpack Summary
Continued light to moderate snowfall over the past few days has accumulated 30-60cm of storm snow that has been redistributed by predominantly southwest and southeast winds. 2000m and below, the storm snow lies above a crust that formed last week. A rain crust that was buried mid March is now 90-120 cm deep. The mid-February crust/facet layer can still be found at the upper end of tree line and into the alpine. This interface is generally 120-170 cm deep but may be present nearer to the surface in wind scoured areas. Although there is growing confidence that this layer is becoming dormant, a storm slab or cornice release in the right location may have the potential to trigger any of the deeply buried weak layers.
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.
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.