Avalanche Forecast
Issued: Dec 3rd, 2021 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Wind Slabs.
ahanna,
Avalanche Canada
Shifting winds may form fresh wind slabs on new aspects. Be alert to conditions that change with elevation as you get above the trees.
Summary
Confidence
Weather Forecast
Friday night: Increasing cloud. Light wind. Freezing level valley bottom.
Saturday: Flurries, trace. Light to moderate winds shifting northwest. Treeline high temperature around -9.
Sunday: Mainly sunny. Light to moderate northwest wind. Treeline high temperature around -8.
Monday: Trace overnight then mainly sunny. Light wind. Treeline high temperature around -8.
Avalanche Summary
A widespread natural storm slab avalanche cycle up to size 3.5 occurred over Tuesday night, a mixture of wet and dry releases, depending on aspect and elevation. On Thursday, explosive cornice control work produced several size 2 cornices, some of which triggered storm slabs on the slopes below.
Although our natural avalanche cycle is over, concern for alpine and upper treeline areas is renewed by the presence of new wind slabs from recent westerly winds.
Snowpack Summary
About 20 cm of recent low density snow has been wind loaded into lee terrain features by westerly winds in the alpine and upper treeline. Wind slabs may see some redistribution Saturday as winds shift northwest. Below 2100 meters, this overlies a moist upper snowpack which is likely solidifying in the cold temperatures. Rain-wetted surfaces below 1700 m have refrozen into a thick, supportive crust that should effectively lock the snowpack in place at lower elevations.
Numerous snow profiles in the Whistler area on Thursday yielded no significant shears on weak layers that existed in advance of the storm, meaning we can cautiously reclassify persistent weak layers like our mid-November crust/facets and late-November surface hoar as dormant. Places to avoid testing this idea would include steep, shallow snowpack areas above 2100 meters.
Average snow depths at treeline are now likely closer to 150-200 cm, with a whopping 450+ cm above 1900 metres. Snowpack depths taper dramatically to below threshold very near the treeline/below treeline boundary.
Terrain and Travel
- Be alert to conditions that change with elevation and wind exposure.
- Recent wind has varied in direction so watch for wind slabs on all aspects.
- When a thick, melt-freeze surface crust is present, avalanche activity is unlikely.
- Pay attention to cornices and give them a wide berth when traveling on or below ridges.
Problems
Wind Slabs
As upper level winds shift northwest Saturday, any available soft snow in the alpine may be reverse-loaded into new features. Human triggering potential exists for these new wind slabs as well as older wind slabs from previous westerly winds.
Cornices have grown recently and have proven to be reactive to human and explosive loads.
Aspects: North, North East, East, South East, South.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Dec 4th, 2021 4:00PM
