Conditions will be prime for the rapid formation of touchy new storm slabs on Saturday. Manage your exposure by seeking out simple terrain and factoring in the possibility for storm slabs to step down to deeper layers.
Confidence
Moderate - Forecast snowfall amounts are uncertain
Weather Forecast
Friday night: Cloudy with increasing flurries bringing about 15 cm of new snow by morning. Light to moderate south winds.Saturday: Cloudy with continuing snowfall bringing another 20-25 cm of new snow. Moderate to strong southwest winds, increasing over the day. Alpine high temperatures around -4 as freezing levels rise to 1500 metres.Sunday: Mainly cloudy with isolated flurries and a trace of new snow. Mainly light northwest winds, easing over the day. Alpine high temperatures around -10Monday: A mix of sun and cloud. Light west winds. Alpine high temperatures around -13.
Avalanche Summary
Avalanche activity on Wednesday and Thursday was limited to a few small wind slabs, loose dry releases, and one large cornice pried out by explosive control work near ridgecrest. Monday was similar with riders triggering small loose dry avalanches in steep terrain as the storm snow sluffed away. The last reported persistent slab activity was on Sunday when a few large (size 3) persistent slab avalanches were observed on south facing alpine features. This was the final report from a widespread persistent slab avalanche cycle that was quite active last week, particularly in the Selkirks and the northern tip of the Monashees.Looking forward, increasing snowfall, wind, and freezing levels are setting up conditions ideal for the formation of storm slabs and natural avalanche activity. Although the likelihood of storm slabs 'stepping down' to deeper persistent slab problems is in question, travel plans should account for very large avalanches as the possible result.
Snowpack Summary
A building storm is now depositing new snow on the surface. Below the new snow, 10 to 20 cm of older low density snow sits above old wind slabs in the alpine, and in some isolated areas above small surface hoar (feathery crystals).A weak layer that formed during the dry spell in early December is now 80 to 120 cm deep. The layer is composed of weak facets, surface hoar, and a sun crust on steep south-facing slopes. This layer was previously responsible for large persistent slab avalanches, but activity has greatly diminished over the last week. Saturday's storm may breathe some life into it, the places of greatest concern will be north and east facing slopes between 1900-2300 m and steep south-facing slopes in the alpine.The lower snowpack is generally strong and settled, with a crust that formed in late October near the bottom of the snowpack.
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.
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.