Regions
Banff Yoho Kootenay.
Widespread Natural Avalanches continued through Saturday. Cooling Sunday should slow this activity but the snowpack will not completely recover by the time the sun returns on Monday. AVOID ALL AVALANCHE TERRAIN even if you are just hiking down low.
Weather Forecast
Rain and with high freezing levels continued to add heat to the snowpack Saturday. Cooler temps Sunday morning should lead a light freeze TL and above with 5 to 10 cm accumulating. Rain will likely keep travel poor BTL. The first freeze to valley bottom in quite a while is forecast for Monday however solar inputs may quickly weaken new crusts.
Snowpack Summary
Moist surface snow to mountain top for all but the highest peaks. Un-supportive, isothermal conditions exist to around 2500m. The basal weakness persists in the alpine and at treeline and is reactive to large triggers and has been failing with the warm temperatures, solar inputs and rain over the last 4 days. Travel is poor.
Avalanche Summary
Avalanches are running far initiating as wet slabs at TL or the alpine as wet slabs and running well below treeline into hiking terrain. Thursday explosive brought down size 3-4 wet slab avalanches from the alpine over bare ground BTL. It's a good time to AVOID AVALANCHE TERRAIN completely.
Problems
Wet Slabs
Wet Slab avalanches are the release of a cohesive layer of snow (a slab) that is generally moist or wet when the flow of liquid water weakens the bond between the slab and the surface below (snow or ground). They often occur during prolonged warming events and/or rain-on-snow events. Wet Slabs can be very unpredictable and destructive.
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.
Cornices
Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.