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Avalanche Forecast

Archived

Dec 2nd, 2021–Dec 3rd, 2021

Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely.
Below Treeline
Natural avalanches unlikely.

Regions

Sea To Sky.

Westerly winds were actively forming new wind slabs over the day on Thursday. Raise your guard as you reach upper treeline and alpine elevations.

Confidence

High -

Weather Forecast

Thursday night: Clear. Light northwest winds.

Friday: Mainly sunny, clouding over in the evening. Light west winds. Treeline high temperatures around -7.

Saturday: Clearing from overnight cloud and isolated flurries. Light variable winds, increasing and shifting northwest. Treeline high temperatures around -9.

Sunday: Mainly sunny. Light northwest winds. Treeline high temperatures around -8.

Avalanche Summary

A natural storm slab avalanche cycle occurred over Tuesday night. Details are still limited but it's safe to assume numerous large or even very large avalanches occurred during this period. A report from the Rutherford/Ipsoot area Thursday described a mixture of wet and dry releases, depending on aspect and elevation. These reached size 3 (very large).

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 west winds.

Snowpack Summary

About 20 cm of low density snow has been redistributed by recent westerly winds in exposed areas in the alpine. Below 2100 metres, this overlies up to two metres of moist snow from rain during Tuesday night's atmospheric river. The refrozen surface crust from this event is supportive from the lower extent of the snowpack to about 1700 metres. 

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 metres.

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 for avalanches very near the treeline/below treeline boundary.

Terrain and Travel

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Watch for areas of hard wind slab on alpine features.
  • When a thick, melt-freeze surface crust is present, avalanche activity is unlikely.

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.