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
TUESDAY: Cloudy, light west winds, alpine temperatures around -8.WEDNESDAY: Cloudy, moderate southwest winds, alpine temperatures around -6.THURSDAY: Cloudy with isolated flurries, moderate to strong southwest winds, alpine temperatures around -4.
Avalanche Summary
Recent avalanche reports are limited to a size 1 skier triggered slab avalanche on a southeast aspect at 1350 m in the Howsons. Last week, a large deep persistent slab avalanche was reported in the Smithers area that released on weak snow near 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
5-20 cm of settled storm snow sits above a widespread rain crust up to about 1300 m. Recent winds have likely formed wind slabs on lee and cross loaded features. Several buried surface hoar layers have been reported 40-80 cm deep and have given variable results in snowpack tests. Many areas have hard slabs in the upper snowpack above weak sugary snow near the ground. Triggering a deep persistent slab above this sugary snow will remain a low probability high consequence scenario for some time.
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.