Regions
Banff Yoho Kootenay.
With elevated winds, we are seeing isolated natural avalanches that are hard to predict. Be suspect of slopes where a slab sits over the weaker layers below, and watch how any winds are loading alpine features. SH
Weather Forecast
West winds could reach 100kph at 3000m and temperatures will be in the -5C to -9C range for Sunday. 5-8cm is currently in the forecast for Monday.
Snowpack Summary
10 to 20cm of wind blown snow from last week overlies a generally weak and facetted mid-pack and base - particularly in the Lake Louise area and on the E side of Hwy 93N. Near the divide,deeper snowpacks are stronger and more supportive. Surface hoar up to 10mm was buried by a trace in some areas and blown away in others by strong W winds Saturday.
Avalanche Summary
Yesterday a new 300m wide fracture line was spotted at treeline/low alpine near Cathedral Peak. This was a N-NE aspect and was 50cm deep. A few other healthy sized 2 slides were noted in the Lake Lousie backcountry today. 2 were new wind slabs, and 1 was a deep persistent slab on Fossil Peak. We suspect the increase in winds triggered the slides.
Confidence
Timing, track, or intensity of incoming weather system is uncertain on Sunday
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.