Regions
Banff Yoho Kootenay.
While human triggering of avalanches is becoming less likely, the potential for wide propagation still exists, be cautious in open terrain. JH
Weather Forecast
Slight warming (highs of -7 at Bow Summit on Thursday), increasing west/northwest wind (Moderate to Strong on Thursday), cloudy skies and light flurries are forecast through the rest of the week.
Snowpack Summary
Wind slabs in alpine and tree line areas are now stubborn to trigger. The Jan 6 surface hoar/facet/sun crust layer, down 30-60cm, has becoming less reactive to skier triggering, however sudden collapse results persist on both the Jan 6 and Dec 3 layers. Isolated whumphing on mid-pack facets/surface hoar were observed yesterday.
Avalanche Summary
Avalanche control using explosives at local ski resorts on Tuesday produced windslab up to size 1.5, and an isolated size 2.0 persistent slab avalanche on a West aspect in the alpine. Lots of evidence of the previous widespread natural avalanche cycle up to size 3 on all aspects with some very large propagations.
Problems
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.
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.