Regions
Banff Yoho Kootenay.
Watch for an increase in the hazard on Sunday as the expected new snow adds load to the weak layers in the snowpack.
Weather Forecast
Continued Moderate SW winds at ridgetop elevation Saturday under mainly sunny skies. Moisture reaches the divide late in the afternoon Saturday bringing up to 20cm of snow on Sunday with the temperatures rising to near 0 in the valley bottoms and winds increasing around mid day. The precip should fade Sunday night with only a trace expected Monday.
Snowpack Summary
A trace of new snow on facets, isolated surface hoar, and sun crusts on steep South slopes. The snowpack is generally weak and facetted throughout. The Dec 18 interface is evident down 20-40 cm and is still a concern in deeper snowpack areas, but in shallower areas is facetting out. Some hard wind slabs exist in immediate lees of alpine terrain.
Avalanche Summary
No natural avalanche activity observed in past 72 hrs.
Confidence
Intensity of incoming weather systems is uncertain on Sunday
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.
Deep Persistent Slabs
Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.