Confidence
Fair - Freezing levels are uncertain on Thursday
Weather Forecast
Tuesday: light snowfall in the evening / moderate southwest winds / freezing level at 1000m Wednesday: light snowfall in the morning with clearing by the afternoon / light southwest winds / freezing level at 800m Thursday: clear / light southwest winds / freezing level climbing throughout the day to 1200m
Avalanche Summary
In response to the strong winds, heavy precipitation and unexpected warming over the weekend a wide spread avalanche cycle was reported in the Coquihalla area on Sunday. Numerous size 2-2.5 and a few size 3-4 avalanches were observed. In the Duffey area numerous size 1.5-2 avalanches occurred on Sunday.
Snowpack Summary
On saturday night and sunday the region saw moderate to strong southwest winds and moderate precipitation (heavy precip in the Coquihalla). For most of the period rain fell to about 1700m, but freezing levels fluctuated during the storm. In the Duffey Lake area light amounts of new snow sit above a new rain crust that has formed below 1700m while cohesive stubborn windslabs exist at higher elevations.In the Coquihalla area temperatures were still closer to 0.0 on Monday. The warmer present temperatures combined with the higher snowfall/rain values in this area means that deep and destructive wind slabs that formed in the wake of the heavy rain will be slower to stabilize.With the recent wind and snowfall there are widespread unstable cornices. Any cornice fall would be destructive by itself, but could also be a trigger for the slope below. Persistent weak layers lower down in the snowpack have generally ceased to be of concern, except perhaps in very isolated, thin rocky areas. Most recently, the Coquihalla area has been receiving the most snowfall with current snowpack depths at treeline amounting to 390cm. In the Duffey Lake area, treeline depths are closer to 240cm.
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.
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.