New storm snow with strong winds will quickly increase the hazard on Tuesday.
Confidence
Fair - Timing, track, or intensity of incoming weather system is uncertain
Weather Forecast
A warm front will bring precipitation and rising freezing levels to the South Coast on Tuesday. The north of the region is expected to see 10-15mm of precipitation whereas the south may see 20-30mm. Freezing levels are expected to reach between 1600 and 1800m and alpine winds should be strong from the SW. On Wednesday, light precipitation is expected to continue (3-6mm) with freezing levels dropping to around 1000m and winds easing to light in the alpine. Christmas day looks to be mostly sunny with freezing levels around 700m and light NW wind in the alpine.
Avalanche Summary
A report from Monday of storm slabs up to size 2 being remote-triggering from flat areas up to 75m away. This was reported in the NE part of the Coquihalla area. Slabs were 40-60cm thick and were releasing on the crust/surface hoar layer. On Sunday, natural storm slab activity up to size 2 were reported at treeline and in the alpine. Natural activity is expected again on Tuesday with additional storm loading.
Snowpack Summary
The new storm slab is typically 40-60 cm thick and sits on the rain crust/surface hoar layer that formed last week. The crust typically extends to around 2200m elevation and the surface hoar that sits above is typically 2-5mm where it exists. In some areas, the new snow may be well bonded to this layer but in other areas the layer remains highly reactive so some local investigating may be required. Strong forecast winds on Tuesday are expected to quickly form touchy new wind slabs. The November crust is deeply buried near the ground and while triggering this layer is generally unlikely, the likelihood of triggering does increase during the storm with the additional weight of the new snow.
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.