Regions
Banff Yoho Kootenay.
Some light snow and strong winds are keeping the sensitivity of the Dec.19th facet interface elevated. Reports of whumpfing, cracking and natural avalanches over the last 12 hours. Its a tricky time for assessing this problem. SH
Weather Forecast
Continued strong Westerly winds Wednesday and light snow. Thursday another pulse of snow (10cm) along the divide. Alpine temperatures will stay in the -12 to -15C range and will cool off Friday as a NW flow begins to take over.
Snowpack Summary
Strong winds and light snow accumulations have formed thin wind slabs 10-20cm thick in alpine lees. These sit over previous slabs up to 60cm thick at treeline and above. These wind slabs sit over the poorly bonded Dec.19 facets. The Nov crust is 30-80cm deep. While it is not currently producing avalanches, we expect it could with more snow load.
Avalanche Summary
Numerous size 1.5 - 2 avalanches were observed between Bow Summit and Lake Louise on peaks such as Observation, Crowfoot and Dolomite. These slides appeared to be 24 hours old. As well, 2 naturals were observed off of the N. side of Mt. Fairview today. They were likely initiated by wind transport but the failure layer is unknown.
Confidence
Due to the number and quality of field observations on Tuesday
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.