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Avalanche Forecast

Archived

Dec 25th, 2021–Dec 26th, 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 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

South Rockies.

Reactive storm slabs may linger as snowfall tapers through Sunday. Be aware of ongoing slab development in windy areas.

Confidence

Moderate -

Weather Forecast

Saturday night: Cold with starry breaks and isolated flurries, 5-10 cm. Light, gusty south wind. Overnight lows dropping to -28.

Sunday: Cloudy with isolated flurries, up to 5 cm. Light to moderate southeast wind. High temperature of-22, possible inversion.

Monday: Cold and cloudy with sunny breaks. Light, wind and cold temperatures with a high of -21.

Tuesday: Mix of sun, cloud, and isolated flurries. Light, gusty winds and cold temperatures with a high of -22.

Avalanche Summary

On Friday, a small (size 1) storm slab was reported triggered by skier traffic. Otherwise, riders reported loose-dry sluffing with the new snow.

On Thursday, explosives triggered a few small (size 1) storm slab avalanches. On Wednesday, the South Rockies field team reported several wind slabs that appeared to have slid on the early December crust and up to size 2. 

Snowpack Summary

25-45 cm low density snow arrived Christmas morning with storm totals over 60-100 cm in the last week. Gusty winds have produced variable storm slabs and cross-loaded terrain features. In some wind exposed areas surfaces have likely been stripped back down to older wind slabs and the early December crust. Sheltered areas may still hold loose snow. A lot of variability exists.

A crust from early December is now 60-100 cm below the surface, and is found up to 2400 m. A layer of weak facets (sugary snow) has been reported above and below this crust. This is the layer of concern in our persistent avalanche problem, snowpack tests are generally showing hard results on this interface, however, areas, where avalanches have recently failed on this crust, continue to be problematic once reloaded with new snow. 

Below 2300 m, several early-season crusts make up the lower snowpack. Snowpack depths range from 80-150 cm at treeline elevations and taper quickly below 1900m.

Terrain and Travel

  • Continue to make conservative terrain choices while the storm snow settles and stabilizes.
  • Fresh wind slabs will likely form throughout the day, diligently watch for changing conditions.
  • Start with conservative lines and watch for clues of instability.
  • Be aware of the potential for large avalanches due to the presence of a persistent slab.

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.

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.