Storm slabs continue to develop at higher elevations and will be reactive to human-triggering on Wednesday. Conservative terrain choices remain critical.
Confidence
Moderate - Timing, track, or intensity of incoming weather system is uncertain
Weather Forecast
The next storm pulse is expected to arrive Tuesday overnight and is expected to bring 15-30cm of new snow by Wednesday afternoon. Amounts are expected to be greatest to the south of the region. Alpine winds are forecast to be moderate from the south and freezing levels could reach as high as 2000m. A bit of a break is expected Wednesday afternoon or evening but the next storm pulse arrives Wednesday night. Another 10-20cm is expected by Thursday morning with freezing levels as high as 2000m and moderate alpine wind from the south. Unsettled conditions and light flurries are expected during the day on Thursday and on Friday. Freezing levels are forecast to fall below 1500m and alpine winds should generally be light.
Avalanche Summary
On Monday, a skier triggered a chunk of cornice which initiated a size 1 storm slab avalanche on the slope below. This occurred on a north aspect at 1900m. A natural cornice release also triggered a size 2 storm slab on north aspect at 1900m. The storm slab was 15-30cm thick. On Sunday, ski cutting produced several size 1-1.5 avalanches. This includes soft storm slabs up to 30cm thick, wind slabs in lee and cross loaded features, and loose wet avalanches at lower elevations. Explosives also released a couple size 2 cornices which triggered soft slab avalanches on the slopes below. Rain-soaked lower elevations are unlikely to see much in the way of avalanche activity on Wednesday, but storm slab avalanches are expected to be reactive to human-triggering at higher elevations with ongoing snowfall and wind continuing overnight Tuesday and Wednesday. Cornices are reported to large and fragile, and may fail under the weight of a person.
Snowpack Summary
50-70cm of new snow has accumulated in the last week and overlies a thick melt-freeze crust which extends into the alpine. The snow is reported to be bonding well to the crust and recent avalanches have been failing within the recent storm snow, not on the crust interface. Moderate wind loading and cornice development have both been reported over the last few days. Moist snow is being reported up to around 1800m on Sunday. Rain will continue to soak lower elevations on Wednesday. The weak surface hoar layer from early January can be found down over a meter and is still reactive in isolated snowpack tests but triggering an avalanche on this layer has become unlikely.
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.