Regions
Banff Yoho Kootenay.
Avalanche control on Mt Stephen and Mt. Field in Yoho and Mt. Hector, on Hwy 93N Thursday, Mar 9. No activities in these areas during that day.
Weather Forecast
Light winds and -10C at treeline with only a trace of snow for Thursday. Friday another pulse of snow (10-12mm) along the divide and increased alpine winds into the moderate to strong range.
Snowpack Summary
50-60cm of storm snow has developed into a storm slab that is sensitive to triggers at treeline and above. This sits over a supportive mid-pack, with the lower half of the snowpack consisting of weak facets and depth hoar. There is isolated wind effect only near ridge crests as of Wednesday.
Avalanche Summary
Over the last few days there have been many larger than expected avalanches to size 3 within the storm snow from avalanche control as well as naturals. Some have been seen to step down to the deeper weak layers.
Confidence
Due to the number of field observations
Problems
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.