Regions
Banff Yoho Kootenay.
Flights across the park today in good visibility showed clear evidence of recent avalanche activity - up to size 3 (large) avalanches in the last 48-hours. We remain concerned for human triggering on all steep start zone areas at higher elevations.
Weather Forecast
A stable week ahead as the NW flow persists keeping the air cool with light winds. No snow in the forecast until Friday, and temperatures this week will range from -5 to -10. All told an uneventful week ahead for weather.
Snowpack Summary
Wind slabs are present in many open areas above tree line. Below this, the snow pack is quite weak and facetted in most places. The Dec 18 crust/facet/surface hoar interface is down 30-40cm at tree line. Backcountry users are experiencing widespread of whumphing on this layer. The bottom half of the snow pack consists of facets and depth hoar.
Avalanche Summary
Flights over the park today with good visibility revealed a widespread natural avalanche cycle over the past 48-hours. Wide propagations at treeline and above up to size 3, many running to the bottom of the runout zones.
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.