Regions
Northwest Inland.
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 with thicker valley cloud due to an alpine temperature inversion. Light to moderate southwest winds. Freezing level rising from 2200 to 3400 metres over the day with alpine temperatures rising from around 0 to +5. Cooler temperatures at valley bottom.Thursday: Mainly sunny with some valley cloud due to lingering temperature inversion. Light to moderate southwest winds. Freezing level to 3500 metres with alpine temperatures around +7. Cooler temperatures at valley bottom.Friday: A mix of sun and cloud. Strong southwest winds. Freezing level around 2500 metres with alpine temperatures around +5. Freezing level and temperatures will drop over the day as the temperature inversion breaks down.
Avalanche Summary
No recent avalanche activity has been reported. Stiff wind slabs now exist at treeline and in the alpine on leeward slopes and cross-loaded features. If triggered, these could step down to trigger deeper weak layers and initiate large avalanches. The last significant avalanche observation was submitted on November 28th from Skilokis Creek. Here, a size 2.5 persistent slab was triggered from 150 m away. The possibility for further persistent slab releases will increase with forecast warming.
Snowpack Summary
Average snowpack depths now total 80-140 cm at treeline elevations and up to 160 cm in the alpine. (Depths of up to 210 cm have been reported from the Howsons.) Wind effect from recent strong southwest to northwest winds extended down into treeline elevations and resulted in fairly extensive wind slab formation. Below the wind-affected surface, approximately 30-50 cm of recent snow now overlies two crusts that were buried near the end of November. These crusts are widespread and extend into the alpine. Recent snowpack tests have shown sudden results at these crust interfaces. Below these crusts, we have a well settled midpack overlying the late October crust near the base of the snowpack. This "crust/facet combo" is widespread and has been reactive to rider and remote triggers.
Problems
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.
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.