Avalanche Forecast

Archived

Dec 27th, 2021–Dec 28th, 2021

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, human triggered possible.

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely.

Regions

Purcells.

Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.

Keep in mind that cold temperatures significantly increase the consequence of even minor injuries in the backcountry.

Confidence

Moderate - Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast.

Weather Forecast

MONDAY NIGHT: Partly cloudy / Light west wind / Low of -25

TUESDAY: Mostly cloudy / Light northwest wind / High of -19

WEDNESDAY: Sunny / Light northwest wind / High of -21

THURSDAY: Mostly cloudy / Light to moderate northwest wind / High of -20

Avalanche Summary

Numerous skier triggered size 1 dry loose avalanches were reported on Sunday. Expect dry loose avalanches (sluffing) running far and fast in steep terrain.

Explosive work near Invermere continues to produce avalanches on the reloaded bed surface of the crust-facet layer formed in early December, found 40-70 cm deep in that area.

Snowpack Summary

Variable wind direction has resulted in redistribution of 20-60 cm of recent snow at upper elevations. The recent snow may sit over a layer of weak surface hoar crystals at treeline and below. Expect dry loose avalanches (sluffing) running far and fast in steep terrain.

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

Use small low consequence slopes to test the bond of the new snow.
Pay attention to the wind, once it starts to blow fresh sensitive wind slabs are likely to form.
Recent wind has varied in direction so watch for wind slabs on all aspects.
If triggered, loose dry avalanches may step down to deeper layers resulting in large avalanches.
Be aware of the potential for loose avalanches in steep terrain where snow hasn't formed a slab.

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.