Regions
Banff Yoho Kootenay.
With new snow, warming temperatures and strong W winds forecast for Sunday afternoon, it will be important to watch the local snowfall amounts and wind loading in the areas you are traveling in and reduce your exposure as the hazard increases.
Weather Forecast
A storm is forecast to arrive by mid day on Sunday bringing 10-20cm of new snow and very strong West winds at ridge top near the divide. Less snow is forecast in eastern areas. The winds ease off a little on Monday and switch to the NW with a few more cm`s of snow forecast for Monday and Tuesday. Treeline temperatures remain between -4 and -10`C.
Snowpack Summary
A trace of new snow over facets, surface hoar, or sun crust 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. In shallower areas the slab above this has facetted out. Wind slabs exist in many open areas above tree line.
Avalanche Summary
No natural avalanche activity observed in past 72 hrs.
Confidence
Intensity of incoming weather systems is uncertain on Sunday
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.
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.