Strong to extreme southerly winds overnight will have created fresh wind slabs in the alpine and tree-line elevations. Below tree-line, warm temps have created a soft slab overlying a touchy surface hoar layer.
Weather Forecast
Strong to extreme winds from the SW will die down this morning, accompanied by a general cooling over the next couple of days. Alpine highs today of -7*C, winds dropping from strong SW to moderate NW during the day, and isolated flurries. Calm and cooler Monday, with light SW winds, trace amounts of snow, and alpine highs of -8*C.
Snowpack Summary
In specific locations, strong to extreme S winds have redistributed storm snow and created loaded pockets and wind slabs on lee and cross-loaded features at treeline and above. The Jan 17 persistent weak layer down 30cm is surface hoar in sheltered areas and sun crust on solar aspects. The overlying 30cm has settled into a cohesive soft slab.
Avalanche Summary
Several natural loose and small slab avalanches to sz 2 were observed on steep solar aspects off of Mt Tupper yesterday. Field teams were able to easily trigger 10-15cm deep soft slabs, 5-10m wide, on N-facing convexities. Fast-moving, dry loose sluffs were observed below tree-line in steep, confined gullies.
Confidence
Wind effect is extremely variable
Problems
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.
Wind Slabs
Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.