Regions
Kootenay Boundary.
We're in an incremental loading pattern--avalanches have just started to run on the early February weak layer. Check the Forecaster Blog for further discussion.
Confidence
Fair - Timing, track, or intensity of incoming weather is uncertain
Weather Forecast
A moist, northwesterly airflow has set up over the region, bringing a series of weak pulses of precipitation over the next few days. Snow amounts look to be in the region of 2-4 cm each day for Sunday, Monday and Tuesday. A more punchy storm is currently forecast for Tuesday night, which may bring more like 10-15 cm. Freezing levels from now until Tuesday afternoon will hover between 500-1000 m. Winds should stay mostly light or moderate, blowing from the west or northwest.
Avalanche Summary
Snow amounts over the early Feb weak layer reached threshold in many places on Saturday. Natural avalanches were observed in the storm snow to size 1.5. Avalanche control at Kootenay Pass produced avalanches up to size 2 running on a crust buried around 35 cm below the surface.
Snowpack Summary
Saturday's storm brought around 15 cm new snow, bringing the gradually incrementing snow amounts above the early Feburary surface hoar layer to around 30 cm. Alpine winds have been strong enough to blow snow around and touchy wind slabs have formed predominantly on northerly and easterly aspects. The early February weak layer comprises large surface hoar on sheltered aspects, facets on northerly aspects and a crust on solar aspects. In shallow snowpack areas concerns remain for the mid-December persistent weakness down around 80-100cm and for basal facets. Treeline snowpack depths are approximately 230 cm.
Problems
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.
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.