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Avalanche Forecast

Archived

Dec 25th, 2021–Dec 26th, 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 unlikely, human triggered possible.
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.

Regions

Purcells.

Be aware of changing avalanche conditions as you gain elevation. Recent snow sits over a weak layer in the trees and wind slabs have been reactive up high. As temperatures drop, make sure to keep an eye on the daylight and leave plenty of time to get home safely.

Confidence

Moderate - Uncertainty is due to how quickly the snowpack will recover and gain strength.

Weather Forecast

Flurries tapering and cold temperatures setting in.

Saturday night: Cloudy with scattered flurries, 5 cm. Light to moderate southwest wind. Treeline temperature around -14 C.

Sunday: Mostly cloudy with scattered flurries, 5 cm. Light to moderate southwest wind. Treeline temperature around -18 C.

Monday: Mix of sun and cloud. Light variable wind. Treeline temperature around -20 C. 

Tuesday: Mix of sun and cloud. Light variable wind. Treeline temperature around -24 C. 

Avalanche Summary

On Friday, size 1 wind and storm slab avalanches were reactive to skiers and explosives, additionally a couple of natural size 1 wind slab avalanches were reported on a northeast aspect at 2450m.

Explosives Wednesday, Thursday, and Friday continued to trigger size 1-2 persistent slab avalanches at treeline elevations near Invermere, these failed on the crust-facet layer 40-70 cm deep.

On Wednesday, a few small (up to size 1) natural and human-triggered wind slab avalanches were reported. 

Snowpack Summary

20-60 cm of recent snow has seen some redistribution at upper elevations, forming deep, soft deposits in leeward terrain features. The recent snow may sit over a layer of weak surface hoar crystals at treeline and below. 

The upper snowpack overlies a substantial crust from early December. This crust is approximately 60-120 cm below the surface, 10-30 cm thick on average, and is present across all aspects to at least 2300 m. A layer of weak facets (sugary snow) has been reported above this crust. Snowpack tests are generally showing hard results on this interface.

A late October facet/crust layer of concern sits at the bottom of the snowpack above 1900m. Although this layer has been trending less reactive, it remains on our radar.

The snowpack depth at treeline is around 120-250 cm. The deepest snowpack can be found in the southern half of the region. 

Terrain and Travel

  • Stay off recently wind loaded slopes until they have had a chance to stabilize.
  • Approach steep open slopes at and below treeline cautiously, buried surface hoar may exist.
  • Be aware of the potential for large avalanches due to the presence of a persistent slab.
  • Continue to make conservative terrain choices while the storm snow settles and stabilizes.

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.

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.