Regions
Northwest Inland.
Conditions are improving, but the consequence of triggering a large persistent slab avalanche warrants a cautious approach to steep open terrain
Confidence
Moderate - Due to the number of field observations
Weather Forecast
MONDAY: Cloudy with sunny periods, light west winds, alpine temperatures around -8.TUESDAY: Mainly cloudy, light west winds, alpine temperatures around -10.WEDNESDAY: Cloudy with isolated flurries, moderate southwest winds, alpine temperatures around -8.
Avalanche Summary
Recent avalanche reports are limited to evidence of natural activity that occurred during last week's storm. This includes a large deep persistent slab avalanche in the Smithers area that released on weak snow near the the ground. The avalanche occurred on a cross-loaded feature, and was likely triggered by a smaller wind slab stepping down to weak basal facets over a metre deep.Looking ahead, triggering wind slabs as well as lingering persistent slabs remains a possibility at higher elevations.
Snowpack Summary
Last week's storm delivered 20-30 cm in the Smithers area and up to 40 cm or more in deeper areas to the north and west. Freezing levels reached up to around 1600 m, which has left a hard rain crust at lower elevations. Wind slabs may linger at higher elevations, and have potential for wide propagations where they sit above preserved surface hoar from earlier this month. Most areas continue to have a shallow and weak snowpack. Snowpack depths are around 120-150 cm at treeline, with hard slabs in the upper snowpack above weak sugary snow near the ground. Triggering a deep persistent slab will remain a low probability high consequence scenario.
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.