Confidence
Fair - Timing of incoming weather is uncertain on Saturday
Weather Forecast
Another clear and sunny day for Thursday, although high cloud may begin to develop in the afternoon. Mild temperatures are expected in the alpine, due to an above freezing level layer from approximately 1200 to 2200m. Light westerly winds. On Friday, clouds will build during the day but it should remain dry. Freezing levels will be around 2000 m. On Saturday, freezing levels will fall to about 500 m and a frontal system will bring moderate precipitation, which should fall as snow, although there is the possibility for a little bit of rain at the beginning of the storm. Gusty winds will be a feature of the next storm.
Avalanche Summary
There were reports of 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 260cm.The upper snowpack comprises a series of storm snow layers, which have generally bonded well to each other and are now gaining strength. Rain to approximately 2000 m from the last storm that has now refrozen has left us with a crust buried by a skiff of snow. In the alpine, above the elevation where rain fell, fresh new wind slabs have developed in response to very strong winds. Expect winds to shift from southwesterly to northerly, potentially creating some localized reverse loading. Cornices Concern for lower snowpack layers remains only in shallow snowpack areas. Facets associated with a crust from mid-December and/or sugary facets at the base of the snowpack could 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.