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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

South Coast Inland.

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

Moderate - Uncertainty is due to the limited number of field observations.

Weather Forecast

Thursday night: Clear. Light to moderate west winds, easing.

Friday: Sunny, clouding over in the evening. Light variable winds. Treeline high temperatures around -8.

Saturday: Mainly cloudy with isolated flurries continuing from the overnight period, mainly in the south of the region. Light west winds. Treeline high temperatures around -9.

Sunday: Mainly sunny. Light northwest winds. Treeline high temperatures around -10.

Avalanche Summary

Although details are still limited, a natural storm slab avalanche cycle occurred over Tuesday night. A new report from Hurley Pass Thursday morning details a widespread natural avalanche cycle yielding releases to size 3.5 (very large). Similar conditions were very likely in many areas of the region on Tuesday night and sizes suggest that some avalanches involved persistent layers discussed in our snowpack summary.

A report from explosives control in the Duffey Lake area Wednesday showed debris from releases up to size 2 (large) reaching quite low in tracks and runouts, aided by old debris from the last storm's avalanche cycle.

Looking forward, alpine areas remain a concern both for the presence of new wind slabs and for the possibility of persistent slabs remaining reactive to human triggers. Cooling temperatures will aid in stabilizing the snowpack, especially at lower elevations, but the alpine may need more time to adjust to the significant load of new snow.

Snowpack Summary

Moderate to strong westerly winds were observed forming new wind slabs on the surface from upper treeline to alpine in the neighbouring Sea to Sky on Thursday. Similar action was likely taking place farther inland.

The warm, wet storm from early in the week brought 20-30 mm of precipitation to the region. Above an estimated 2100 metres, this fell as snow under the influence of strong southwest winds. This added to the load over a layer of surface hoar now down an estimated 90-120 cm as well as a deeper crust/facet combo layer that produced large avalanches during the region's last storm (Saturday).

Rain-wetted surfaces below about 2100 m have undergone a refreeze that should effectively lock the snowpack in place at lower elevations.

Average snowpack depths in the alpine are now likely closer to 150-200 cm. Below treeline, depths of 30-50 cm have been reported around 500 m, decreasing dramatically with elevation, and still below threshold for avalanches in many areas. Early season hazards such as rocks, stumps, and creeks are still a concern below the alpine.

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.
  • Avoid shallow, rocky areas where the snowpack transitions from thick to thin.
  • 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.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.