Regions
Banff Yoho Kootenay.
The current storm will taper overnight and end by Friday morning, when temperatures cool significantly. However, unstable slabs will continue to exist, and careful snowpack evaluation and route finding will be critical over the next few days.
Weather Forecast
The current storm will continue overnight, tapering early on Friday morning. At this time, the upper level flow will rotate slightly into a NW orientation, and we should expect to see clearing and cooling trend starting on Friday. So, expect another 5-10 cm overnight Thursday, then down to -15 and clearing by Friday morning with strong west winds.
Snowpack Summary
The current storm has so far deposited 15 cm of snow in the last 24-hours, along with strong SW winds and warm temperatures - this combination is creating unstable slabs that overlie a weak layer almost 50 cm below the surface. In some areas, moist surface snow adds to the load and many whumphs were observed today confirming the unstable situation.
Avalanche Summary
Minimal avalanche activity observed today, which is surprising considering the conditions. Several wet loose avalanches were noted in the valley bottoms, and some wet debris was observed in several avalanche paths. Consider that the visibility was poor, so our confidence in these observations is low.
Confidence
Due to the number of field observations
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.