Storm loading will promote touchy conditions on Friday. Expect the avalanche danger to increase throughout the day.
Confidence
Moderate - Timing or intensity of solar radiation is uncertain on Saturday
Weather Forecast
Thursday night: 6-12cm of new snow / Moderate southwest winds / Alpine temperature of -8Friday: 8-15cm of new snow / Strong to extreme southwest winds / Alpine temperatures of -3 (freezing levels at 1500m)Saturday: Clear skies in the morning with increased cloud in the afternoon / Light southwest winds / Alpine temperature of -3Sunday: Light flurries / Light southwest winds / Alpine temperature of -4
Avalanche Summary
On Thursday, our Avalanche Canada Field Team observed evidence of a few naturally triggered size 2 slab avalanches in the Crossing Creek area. While one of the avalanches appeared to have failed within the recent storm snow, one avalanche was about 1m deep and is thought to have been triggered on the December facet layer near the base of the snowpack. This event highlights the isolated yet potentially destructive nature of the deep persistent avalanche problem which should become more prevalent as we head into spring.Looking forward, natural wind slab and storm slab activity is expected to ramp-up again in response to new snow and wind on Thursday night and Friday.
Snowpack Summary
By Friday morning expect 6-12cm of new snow with lots more falling throughout the day. Strong southwest winds are expected to shift these accumulations into much deeper deposits in exposed lee terrain. Over the past week we've had daily snowfalls of 5-15cm bringing the storm total to 50-90 cm. In some areas, the resulting slab may have a poor bond to the old snow interface which consists of stiff wind slabs, crusts, and facets.The mid-pack in this region is generally strong, but the bottom third of the snowpack is composed of weak facets (sugary snow crystals). Approximately 100-120 cm of settled snow sits above this weak layer of sugary, rotten facets that developed in December. This remains a concern and should be on your radar, especially with the recent loading from snow and wind.
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.
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.