The snowpack this year is complex with multiple weak layers. Avalanche control last week showed that these layers can be triggered in certain areas, but variable results make it difficult to forecast where. Conservative terrain selection is a must!
Weather Forecast
We are in the influence of a SW flow with a series of storms moving in off the coast. Expect light snow ~ 5 cm per day for the next three days. Temps will be cool in the -5 to -15 range and winds generally light to moderate from the SW.
Snowpack Summary
Recent winds have developed windslabs on alpine and treeline lee slopes. In sheltered areas the upper snowpack has 30-50cm of soft slab over the Jan 6 surface hoar. The Dec. 15 surface hoar layer is still a concern and is 60-80 cm down and well preserved at treeline and below.
Avalanche Summary
No new avalanche activity reported in this forecast region, however, a size 2 windslab was triggered by a skiier in the lake louise ski hill backcountry. This was in semicircular bowl (approximately 2400m NE aspect).
Confidence
Intensity of incoming weather systems is uncertain
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.