Warming temperatures, heavy snowfall with rapid loading and moderate winds are causing storm slab formation and a spike in avalanche danger.
Weather Forecast
The forecast calls for 16cm more storm snow, alpine high temperature of -4C with freezing level rising to 1300m. Moderate SW winds gusting to strong will accompany the snowfall. Cooling temperatures with clear breaks and light flurries are forecast for Sunday and Monday.
Snowpack Summary
16cm of storm snow so far. Pockets of wind slab are lingering in lee features and cross loaded slopes in the alpine and treeline. The Dec 9 and Nov 21 interfaces are down ~100-120cm and still producing Hard and Sudden test results. We have no persistent weak layers in the upper snowpack.
Avalanche Summary
Size 3 natural avalanches are running out of extreme terrain off Tupper and MacDonald this morning. Yesterday a skier went for a 40m ride on an old wind slab pocket in the Avalanche Mtn Couloir. The slide was size 1 and the skier was uninjured. The slide was 15cm deep and 30m wide and ran on an old faceted crust.
Confidence
Forecast snowfall amounts are uncertain
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.