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Avalanche Forecast

Archived

Dec 11th, 2021–Dec 12th, 2021

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

Regions

South Rockies.

Continue to choose mellow slopes protected from the wind.

Wind and new snow are building slabs that can be triggered by a rider. It is still uncertain how well this new snow is bonding to the snowpack.

Confidence

Low - Uncertainty is due to how the snowpack will react to the forecast weather.

Weather Forecast

SATURDAY NIGHT: Overcast. 5-15 cm of snow expected. Moderate southwest winds, possibly extreme on high peaks. Freezing levels between 1000 and 1500m, starting to drop around midnight.

SUNDAY: Mostly cloudy. 5cm of snow expected. Moderate to strong southwest winds, isolated areas of extreme winds on high peaks. Freezing level 1000-1200m.

MONDAY: Partly cloudy. 0-5 cm of snow expected. Light southeast winds at treeline and strong southwest in the alpine. Alpine high around -4 C. 

TUESDAY: Mostly cloudy. 7-15 cm of snow expected. Light to mod southwest winds. Alpine high around -8 C.

Avalanche Summary

No new avalanches observed. Expect human triggered avalanches to remain likely as the storm snow settles.

There are very few observations at this time, remember that a lack of avalanche observations does not necessarily mean there was a lack of avalanche activity.

Explosive control work earlier this week produced multiple wind slabs to size 1.5, running on the most recent melt freeze crust. 

Snowpack Summary

Moderate to strong southwest winds continue to redistribute 15-25cm of recent storm snow, forming reactive slabs.

Snowpack depths are extremely variable. Before this storm, strong to extreme westerly winds stripped exposed terrain in the treeline and alpine, to the thick and smooth melt freeze crust (December 2nd) or to rock. In sheltered features, the wind has redistributed snow into wind loaded pockets of over 50cm.

Where the December 2nd crust does exist, facets may be forming on top, making this a layer to watch.

The snowpack holds several early season crusts about 20-40cm above the ground below 2300m. 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 30-110 cm at treeline elevations. The snowpack tapers quickly below 1900m.

Terrain and Travel

  • Continue to make conservative terrain choices while the storm snow settles and stabilizes.
  • Closely monitor how the new snow is bonding to the crust.
  • Storm slabs in motion may step down to deeper layers resulting in large 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.