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Avalanche Forecast

Archived

Dec 8th, 2021–Dec 9th, 2021

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

Regions

Lizard-Flathead.

Slabs will continue to be reactive as they sit over a problematic ice crust. Expect variable winds to have loaded unexpected features. 

Give the snowpack time to gain strength before stepping into bigger terrain. Seek out sheltered, low angle terrain for the best riding.

Confidence

Moderate - Uncertainty is due to the speed, direction, or duration of the wind and its effect on the snowpack.

Weather Forecast

Snowfall tapers as the front exits today, replaced by scattered flurries and mixed cloud until a juicer system approaches this weekend.

WEDNESDAY NIGHT: Flurries continue with moderate west-southwest winds. Freezing levels drop to valley bottom. 

THURSDAY: Cloudy with a chance of flurries, light westerlies. Freezing levels at valley bottom. Alpine highs of -8. 

FRIDAY: Trace amounts of snow, most cloudy. Freezing level at valley bottom, alpine highs of -8. Light westerlies. 

SATURDAY: Light to moderate snowfall starts early Saturday morning. Freezing levels climb to 1500m. Alpine highs of -3. Strong to extreme southwest winds. 

Avalanche Summary

A natural size 2 wind slab was observed on Tuesday Dec 7 near Fernie, from a crossloaded treeline feature. Over the last three days, several size 1-1.5 wind slabs have also been skier triggered in immediate lees at treeline and above. 

Numerous small loose dry avalanches have been observed out of steep sheltered terrain features.

All of these avalanches have been triggered on the new snow/ melt freeze crust interface. New snow is bonding poorly to the crust, creating tricky conditions in sheltered and wind affected areas. 

Note there are very few field observations this early in the season. If you venture out into the mountains, please share your observations and/or photos on the Mountain Information Network!

Snowpack Summary

Recent storm snow sits over a thick and supportive melt freeze crust, 5-10cm thick on all aspects below 2400m. Moderate to strong westerly winds have created deeper deposits in lee features in the alpine and treeline. 

The snowpack holds several early season crusts about 20-30cm above the ground. Last week's heavy rain saturated the snowpack and has begun to break down this crust at treeline and below, creating a cohesive lower snowpack.

Snowpack depths range from 10-80 cm at treeline elevations. The snowpack tapers quickly below 1800m, significantly diminished by the rain event. 

Terrain and Travel

  • Closely monitor how the new snow is bonding to the crust.
  • Be careful with wind loaded pockets, especially near ridge crests and roll-overs.
  • Watch for signs of instability like whumpfing, hollow sounds, shooting cracks or recent avalanches.

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.