Regions
Banff Yoho Kootenay.
We have moved to a "Moderate" rating due to lack of natural activity. Keep in mind that the snowpack is inherently very weak, and large avalanches are still possible. If there is a slab overlying facets, its suspect. SH
Weather Forecast
Lows of -20C rising to around -15C with light North winds and sunny skies for Thursday. Some slightly increased winds Friday, but the potential story is significant snow currently in the books for this weekend in some areas. We will see how much actually materializes closer to the time, but stay tuned.
Snowpack Summary
Previous strong to extreme W winds have created harder wind pressed surfaces at treeline and above. Isolated surface hoar may be found buried in sheltered locations at treeline and below. Generally the midpack is weak at TL and above, and the entire snowpack is weak BTL. Near the divide, deeper snow-packs are a bit stronger and more supportive.
Avalanche Summary
We had a small avalanche cycle this past weekend due to big winds, but as temperatures have cooled and winds abated, the activity has slowed down significantly. No new avalanches reported or observed Wednesday.
Confidence
Due to the number and quality of field observations
Problems
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.
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.