Avalanche Forecast

Archived

Dec 29th, 2021–Dec 30th, 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, human triggered possible.

Regions

Purcells.

Westerly winds overnight may form fresh wind slabs on lee features at treeline and above.

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

WEDNESDAY NIGHT: Cloudy / Moderate west wind / Low of -26

THURSDAY: Mix of sun and cloud / Light northwest wind / High of -19

FRIDAY: Sunny / Light northwest wind / High of -20

SATURDAY: Mix of sun and cloud / Strong northwest wind / High of -19

Avalanche Summary

Explosive control work on Tuesday produced several size 2 storm slab avalanches on northerly aspects in the alpine.

Recent explosive control work near Invermere produced large avalanches (size 2) on the crust 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.

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

Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
Recent wind has varied in direction so watch for wind slabs on all aspects.
Be aware of the potential for large avalanches due to the presence of a persistent slab.
Avoid shallow, rocky areas where the snowpack transitions from thick to thin.
Seek out wind sheltered terrain below treeline where you can avoid wind slabs and find great riding.

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.