A bit of new snow combined with sustained winds will keep our wind slab problem alive and well. Even if the rating is still Moderate, stability will be decreasing with any new snowfall.
Confidence
Moderate - Forecast snowfall amounts are uncertain on Monday
Weather Forecast
Sunday: Cloudy with sunny periods and isolated flurries bringing a trace of new snow. Winds light from the southeast. Temperature inversion bringing alpine temperatures to -8.Monday: Mainly cloudy with isolated flurries bringing a trace of new snow. Winds light gusting to extreme from the southwest. Alpine temperatures to -7.Tuesday: A mix of sun and cloud with no new snow. Winds light to moderate from the northeast. Alpine temperatures to -13.
Avalanche Summary
Explosives control in the southern Alberta Rockies produced a Size 2 result in a heavily wind loaded start zone on Friday. A pocket of wind slab released to Size 1 under skier traffic in the same area on Friday. Wind slabs are expected to remain reactive to human triggers with ongoing winds keeping slabs touchy and highly variable snowpack depths keeping trigger points easy to strike.
Snowpack Summary
Recent moderate northerly winds have continued to load our wind slabs on south and west aspects. In some areas these wind slabs may be sitting on an old scoured surface that was stripped by previous strong westerly winds that developed wind slabs on north and east aspects. The newer wind slabs are probably easier to trigger, but the old wind slabs may continue to release with the added load of a rider, especially where they are sitting on a shallow weak sugary base. The mid snowpack is generally right side up, with the mid-December interface down 40-80cms, giving inconsistent results in snowpack tests. There is some faceting below this interface but resistances are good and showing signs of rounding (stabilizing). Travel conditions have been challenging (especially at lower elevations) and little change is expected until a significant warm up helps to settle the snowpack.
Problems
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.
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.