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Avalanche Forecast

Archived

Dec 13th, 2021–Dec 14th, 2021

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

Regions

Purcells.

Continue to make conservative terrain choices. There has been very little break in storms for the snowpack to gain strength. Ongoing moderate winds continue to form rider triggerable slabs.

Confidence

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

Weather Forecast

A nice refresh of snow overnight is the most notable weather in the forecast period. The southeast corner of the region may see stronger wind . The cloud and intermittent light flurries are continuing to hang with us.

MONDAY NIGHT: Mostly cloudy. 3-12 cm snow expected. Moderate south winds, shifting to southeast. Freezing level around 500m.

TUESDAY: Partly cloudy. 0-5 cm of snow expected. Moderate southwest winds. Freezing level rising to 500-900m.

WEDNESDAY: Partly cloudy. Possible trace of snow. Light to moderate southwest winds, westerly at higher elevations. Alpine temperatures around -12

THURSDAY: Partly cloudy. Possible trace of snow. Light southwest wind, trending to strong west at higher elevations in the afternoon. Alpine temperatures around -11.

Avalanche Summary

Avalanche control in the north of the region produced small, skier triggered avalanches on north aspects.

On Sunday, a small, skier remote triggered avalanche was reported that failed on a reloaded bed surface near the base of the snowpack on a north aspect in the alpine. There were other deep failures reported in this region about a week ago. This information is spotty, but it is consistent with a deep persistent problem that may be difficult to trigger. We're not done worrying about this one yet.

Several size 1 and 2 natural avalanches were observed in the north end of the region on Friday. They seem to have failed within the storm snow. 

Snowpack Summary

A refresh of snow overnight keeps the snowpack in a state of change. Where this new snow has been wind transported, it is more likely to form reactive slabs. 

Recently, moderate to strong southwest winds redistributed 30-45cm of snow, forming reactive slabs that still need time to adhere to the rest of the snowpack. 

Down 40-80cm, there is a 10-40 cm thick, solid melt freeze crust on all aspects up to 2400m (December 2nd). 

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

A late October facet/crust layer of concern sits at the bottom of the snowpack above 1900m. This layer has been reactive to human triggers, producing large avalanches. This layer is widespread and will likely continue to be a layer of concern.

Snowpack depth at treeline is 115-200cm, with the deepest snowpack found near the Bugaboos. 

Terrain and Travel

  • Continue to make conservative terrain choices while the storm snow settles and stabilizes.
  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Avoid thin areas like rock outcroppings where you're most likely to trigger avalanches failing on deep weak layers.

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.

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.