Avalanche Forecast
Issued: Dec 5th, 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
Thin pockets of soft wind slab may be surprisingly reactive on Monday. Watch for these fresh deposits in lee terrain features near ridge crest.
Summary
Confidence
Weather Forecast
Sunday night: Flurries up to 5 cm. Light to moderate southwest wind. Treeline temperature around -11.
Monday: New snow 5-10 cm. Light to moderate westerly wind. Treeline high temperature around -8.
Tuesday: Flurries up to 5 cm. Light to moderate southwest wind. Treeline high temperatures around -3.
Wednesday: New snow 10-25 cm. Moderate to strong southwest wind. Treeline high temperatures around -10.
Avalanche Summary
On Saturday, some loose dry sluffing and thin soft slab reactivity were observed in steep terrain and near ridge crests. The slide in this excellent MIN from Garibaldi Park appears to have initiated out of extreme terrain, breaking up quickly and entraining low density surface snow.
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
10-15 cm of new low density snow may sit over a widespread layer of small surface hoar crystals which we will continue to monitor going forward. This sits over wind affected snow in the alpine and a thick, supportive crust below 1700 m. Between 1700-2100 meters, this crust exists shallowly buried by wind affected snow.
Numerous snow profiles in the Whistler area on Thursday yielded no significant shears on weak layers that existed in advance of the previous 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 carefull around freshly wind loaded features.
- Watch for wind-loaded pockets especially around ridgecrest and in extreme terrain.
- Be aware of the potential for loose avalanches in steep terrain where snow hasn't formed a slab.
- Keep in mind the crust offers an excellent bed surface for avalanches.
Problems
Wind Slabs
Small inputs of new snow along with moderate wind will feed wind slabs in the alpine. Watch for fresh deposits in lee terrain features. They may be surprisingly reactive where they sit on a weak layer of surface hoar.
Low density surface snow that hasn't formed a slab may also slide easily on a slippery crust.
Cornices are larger than you may think for this time of year 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 6th, 2021 4:00PM
