Ongoing snowfall and strong southerly winds will keep the hazard HIGH in the alpine on Saturday. Conservative decision making is critical and it is best to stick to mellow terrain.
Confidence
Moderate - Timing, track, or intensity of incoming weather system is uncertain
Weather Forecast
The next storm front should arrive Friday evening and 15-30cm of new snowfall is expected by Saturday morning. Freezing levels are expected to drop to around 1000m and alpine winds are forecast to be strong from south. Another 10-20cm of snowfall is expected on Saturday with freezing levels around 1000m and strong alpine winds from the southwest. Light snowfall is forecast to continue on Saturday overnight and Sunday morning with another 10-20cm of snowfall possible. Periods of clearing are expected between storm pulses over the weekend but there is lots of uncertainty regarding the timing. Unsettled conditions are currently expected for Monday with light snowfall and sunny breaks both possible.
Avalanche Summary
Observations were limited on Thursday due to the stormy conditions but natural storm slab avalanches were reported up to size 2.5. Explosives also triggered numerous storm slab avalanches up to size 2.5. Slab thickness was typically 30-40cm and up to 100cm thick in wind loaded areas. Skiers triggered several small avalanches in wind loaded features and on steep or unsupported features. Loose wet sluffing was reported from lower elevations that saw rain. Storm slabs are expected to remain very touchy to human-triggering on Saturday and natural activity is possible in freshly wind loaded terrain.
Snowpack Summary
Up to 75cm of new storm snow is being reported in sheltered areas with up to 150cm in wind loaded areas. Weaknesses within or at the base of the new storm snow may need a couple days to settle and strengthen. Extreme southerly winds have created very deep and dense slabs in lee terrain, probably well below ridge crests, while scouring windward slopes. Ongoing stormy weather has also encouraged extensive cornice growth. The mid and lower snowpack are strong and well-settled.
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.