Regions
Banff Yoho Kootenay.
We have a classic rockies snowpack, with a weak and faceted lower snowpack, and a mix of old and new wind slabs above. Conservative terrain choices will be your biggest defense against this tricky snowpack that will be here for the winter. LP
Weather Forecast
Moderate west wind at ridge top tomorrow. Another cold night tonight with highs of -15 for tomorrow in the alpine and colder in the valley bottoms. After Thursday temperatures will climb to seasonal norms over the weekend with sunny skies. No snow is in the forecast.
Snowpack Summary
Any of the new snow from the past few days has been blown to smithereens by northern winds at treeline and above. This has produced a reverse loading pattern, with hard slabs in many starting zone areas overlying a weak, faceted snowpack with numerous instabilities in the lower half of the snowpack.
Avalanche Summary
A size 3 was reported on Wednesday on a SE aspect in the Sunshine backcountry which was likely triggered by reverse loading from North winds. Wednesday we also saw some smaller skier triggered wind slabs that were cracking or running a short distance in the Bow Summit area. No new avalanches were reported today.
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.
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.