Regions
Northwest Coastal.
Rapid warming will deliver a stress test to the snowpack on Wednesday. Dial back your terrain selection and be keenly aware of overhead hazards.
Weather Forecast
Wednesday: A mix of sun and cloud. Light to moderate southwest winds. Freezing level rising from 2200 to 3300 metres over the day with a temperature inversion bringing alpine temperatures to around +5. Cooler temperatures at valley bottom.Thursday: Mainly sunny. Moderate south winds. Freezing level to a possible 3500 metres with alpine temperatures around +7. Cooler at valley bottom due to lingering temperature inversion.Friday: A mix of sun and cloud. Strong south winds. Freezing level dropping from 2700 to 1700 metres over the day. Alpine temperatures cooling from +5 to around +3 over the day as the temperature inversion breaks down.
Avalanche Summary
Reports from the Bear Pass area on Monday showed isolated wind slabs releasing naturally to Size 2 from steep, north-facing alpine features. Looking forward to the warming that is forecast for the next couple of days, keep in mind that the strength of the bond between our recent storm snow and deeper buried crusts remains in question (especially at the basal crust). With an increasing possibility for failures at these deep interfaces, it is strongly recommended to take a conservative approach to route selection by traveling through low consequence terrain.
Snowpack Summary
Average snowpack depths in the region are roughly 100-150 cm at treeline elevations. This means that our recent accumulated storm snow (100-130 cm) forms the vast majority of our current snowpack. Strong winds (mainly southwest) over the course of the storm developed deep deposits of wind slab on leeward slopes. The recent snow seems to be settling quickly and sits above a 5-10 cm thick crust that was buried just over a week ago. The crust/facet interface that was buried at the end of October can now be found 90-160 cm deep. Recent snowpack test results have shown hard but sudden results on this interface. The strength of these two deep weak layers will be an increasing concern as the snowpack is forced to adjust to forecast rapid warming.
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.