The last weeks storm cycle has drastically changed the snowpack adding a significant new load. Strong solar warming today will make the new storm slab more reactive.
Weather Forecast
Today we can expect a break from the stormy weather with a sunny day and building cloud in the afternoon. In the alpine the daily high will get up to -7*C, with freezing level to 1300m & winds from the east at 15kph. Tuesday will be more unsettled as a low moves across southern BC bringing light snowfall and 1900m freezing levels to Roger's Pass.
Snowpack Summary
Saturday's storm was the last in a series that brought heavy rain/snow, extreme winds (100+ km/h) and very warm temps. Widespread wind and storm slabs have formed at tree-line and alpine elevations as a result. Below approx. 1700m a rain crust is prevalent. This crust caps a moist upper snowpack.
Avalanche Summary
Natural and artillery controlled avalanches to size 4 were observed on Saturday. The biggest avalanche was Macdonald West Shoulder failing simultaneously in 4 start zones naturally, ripping out mature timber and running to the valley floor. Large fracture lines are visible in the backcountry showing wide propagation and multiple step down layers.
Confidence
Timing or intensity of solar radiation is uncertain
Problems
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.
Persistent Slabs
Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.
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.