Avalanche Forecast
Issued: Dec 4th, 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
Watch for pockets of wind slab in lee terrain features like ridge crests and roll-overs. Wind slabs may remain reactive to human triggers on Sunday.
Summary
Confidence
Moderate - Forecast snowfall amounts are uncertain.
Weather Forecast
Disagreement between weather models has resulted in uncertainty around snowfall amounts Sunday night.
Saturday night: Clear. Light to moderate northwest wind. Treeline high temperature around -9.
Sunday: Mainly sunny. Light to moderate northwest wind. Treeline high temperature around -11.
Monday: Snow overnight 5-10 cm then clearing. Light wind. Treeline temperature warming to around -8.
Tuesday: A mix of sun and cloud. Light to moderate southwest wind. Treeline high temperatures around -3.
Avalanche Summary
On Friday, evidence of a recent size 2 wind slab was observed. The avalanche is suspected to be cornice-triggered and ran full path onto Iceberg Lake. Explosive cornice control work on Thursday and Friday produced several size 2 cornices, some of which triggered storm slabs on the slopes below.
Snowpack Summary
A skiff of new snow sits over a widespread layer of small surface hoar crystals which we will continue to monitor going forward. Dry, wind affected snow can be found in the high alpine. Below 2100 meters, wind-affected snow overlies a thick crust. Below 1700 m a thick, supportive crust caps the snowpack, effectively locking it 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
- Watch for wind-loaded pockets especially around ridgecrest and in extreme terrain.
- 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
Wind slabs in lee terrain features in the alpine may remain sensitive to human triggers.
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 5th, 2021 4:00PM
