Regions
Banff Yoho Kootenay.
While some improvement with cold temperatures on Sunday this will be mainly at lower elevations that have been affected by recent warm conditions. Continue to use caution Treeline and above until a trend away from frequent avalanche activity is seen.
Weather Forecast
Friday saw a the start of a cooling trend. Moderate SW winds will shift to West and increase to strong overnight before shifting NW and back to the light range as the last of the precip arrives Saturday morning ahead of an approaching ridge. Saturday afternoon the ridge will build, skies should clear and temperatures drop into Sunday.
Snowpack Summary
Fresh windslabs and cornice growth in the alpine with 30 to 50 cm since the warming a week ago. A 50-100 cm slab overlies the January 6th weak layer of surface hoar, facets and sun crust and snowpack tests indicate an unstable bond between the two. The lower snowpack is facetted and quite weak in thinner areas but is more settled in thicker areas.
Avalanche Summary
There have been many close calls in the last week indicating that human triggering remains likely in many areas. Yesterday with warming temperatures there were many loose wet or slab avalanches to size 2 out of steep terrain along the divide, and a large natural avalanche out of the National Geographics in the Lake Louise backcountry.
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.
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.