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Avalanche Forecast

Archived

Dec 7th, 2021–Dec 8th, 2021

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

Regions

Lizard-Flathead.

Avalanche danger rises as storm slabs build, bonding poorly to the crust below. Expect greater wind loading at ridge crest and in cross-loaded features. Give the snowpack time to stabilize before stepping into bigger terrain. 

 

Confidence

Moderate - Uncertainty is due to the track & intensity of the incoming weather system.

Weather Forecast

A cold front brings snow and strong winds overnight. Wednesday afternoon will see clearing skies and calmer conditions as the front moves out, replaced by a weak high pressure system.

TUESDAY NIGHT: Snow begins overnight with up to 10cm by Wednesday morning. Increasing southwest winds. Freezing levels at valley bottom. 

WEDNESDAY: Up to 15cm of snow over the day, with strong to extreme southwest winds. Freezing levels rise to 1000m, alpine highs of -5. 

THURSDAY: Light snowfall continues (up to 5cm), with light westerlies. Freezing levels below 500m, alpine highs of -9. 

FRIDAY: Flurries with light westerlies. Freezing levels at valley bottom. Alpine highs of -9.

Avalanche Summary

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

Several small loose dry avalanches have been observed out of steep sheltered terrain features, both skier triggered and natural. 

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

Another 10-25cm of snowfall brings the weeks storm totals to 35-65cm. This low density snow sits over a thick and supportive crust, on all aspects below 2400m. Moderate to strong westerly winds continue to redistribute new snow into deeper deposits in lee features in the alpine and treeline. 

Early season crusts sit 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.
  • Minimize exposure during periods of heavy loading from new snow and wind.
  • 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

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.