Confidence
Fair - Intensity of incoming weather is uncertain
Weather Forecast
Wednesday: Expect flurries to build, with freezing levels reaching 1200m in the afternoon. We could see up to 15cm of new snow with southerly winds up to 50km/h. Thursday / Friday: Continued stormy conditions, with moderate and at times heavy precipitation. The most intense wave looks to arrive Thursday midday. Freezing levels should reach 1000m each afternoon with continued moderate to strong southerly winds.
Avalanche Summary
Loose wet avalanches up to size 2.0 triggered by daytime heating have been reported, as well as isolated cornice releases to size 2.5. The warm weather has increased the glide crack activity with new cracks opening in the Coquihalla area but not actually failing.
Snowpack Summary
The recent warm, clear weather has left us with an aggressive melt freeze crust on solar aspects well into the alpine while shady, dead north slopes cultivated some small surface hoar and remained powdery. These surfaces are newly buried by the arrival of this latest storm. New windslabs are growing in lee locations at ridgecrests. Mature cornices will see further growth under current conditions. Deep, persistent weak layers buried in early February are variable in distribution across the region but remain a key concern. In recent snowpack analysis these layers remain well preserved as surface hoar on north aspects and as a suncrust, facet combo on solar aspects. Although the likelihood of triggering has decreased, the potential for surprisingly large avalanches remains.
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.
Cornices
Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.
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.