Confidence
Fair - Timing, track, or intensity of incoming weather is uncertain on Saturday
Weather Forecast
Friday should be another dry day with some cloud. Freezing levels will be around 2000 near the coast in the morning; further inland an above freezing level layer will give a strong inversion between around 1400 and 2000m. In the afternoon, temperatures will become cooler. Winds will be moderate from the west. On Saturday, around 10 cm of snow is expected with gusty southwesterly winds and freezing levels most likely at valley bottom. On Sunday, strong, gusty winds will likely shift from SW to NW and temperatures will be cold. Flurries or light snowfall is the most likely scenario, moderate snowfall possible.
Avalanche Summary
Two cornice releases were reported from Wednesday, both size 2 on a northeast aspect around 2000m. They only pulled out a very small slab on the slope below, indicating, while cornices are still unstable, the storm snow is gaining strength. Earlier in the week, there were two skier-triggered avalanches near Whistler that went on the recent storm snow interface down around 60 cm, one from Monday and one from Tuesday. Both were size 2 and released on a NE aspect around 2000 m. There have been no recent reports of activity stepping down to any of the lower weak layers in the snowpack.
Snowpack Summary
At treeline, snowpack depths are around 250cm.Warm daytime temperatures and cool overnight temperatures have created a hard, crusty surface layer in many places, even up into the alpine. Surface hoar is growing on this surface, reportedly 3-5mm at this time. While it's on the surface, it obviously doesn't cause us too many problems, but if it is buried with snow, it has the potential to become our next touchy weak layer. The upper snowpack comprises a series of storm snow layers, which have generally bonded well to each other and are now gaining strength. Wind transport in the alpine has been significant in some areas with most wind slab development occurring on north and east aspects, but also some on south aspects. Concern for lower snowpack layers has diminished and remains only in shallow snowpack areas. Facets associated with a crust from mid-December and/or sugary facets at the base of the snowpack may still be a concern in areas you know to be unusually shallow, or where you can see rocks poking up out of the snow.
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.