Regions
Banff Yoho Kootenay.
Warm temperatures and an isothermal snowpack at low elevations is keeping the danger rating high. Avalanche control planned for tomorrow on Mt. Bosworth, Field and Stephen. No activities in these areas.
Weather Forecast
The intense precipitation is starting to taper off. Expect no more than 10cm of snow over the forecast region over the next couple of days with light west wind.
Snowpack Summary
45 - 70 cm of recent storm overlies a crust from January 30th. The recent heavy precipitation, wind and warmer temperatures have created storm slabs which will put an enormous amount of stress on the January 30th crust interface. The basal facets from Nov 6th could reemerge in step down events with this huge stress to the snowpack.
Avalanche Summary
Avalanche control on Mt. Whymper today produced avalanches up to size 2.5. Fracture line thickness varied between 20 and 60cm with average running distance about 250m. Also, evidence of a widespread cycle up to size 3 throughout the forecast region. Some avalanches running close to full path.
Confidence
Freezing levels are uncertain on Sunday
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.