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Avalanche Forecast

Archived

Jan 5th, 2022–Jan 6th, 2022

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

Regions

South Rockies.

As winds pick up ahead of the next storm, fresh, reactive wind slabs will likely form at upper elevations. The region continues to deal with a tricky persistent slab problem and very large avalanches remain possible. Conservative terrain selection remains essential. 

Confidence

Low - Uncertainty is due to the limited number of field observations. Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast.

Weather Forecast

Wednesday night: Increasing cloud. Light NW wind switching SW. Treeline temperature around -22 °C. 

Thursday: Light snowfall 3-6 cm. Moderate SW wind. Treeline high around -14 °C. 

Friday: Snowfall 5-10 cm. Moderate to strong SW wind. Treeline high around -4 °C.

Saturday: Snowfall tapering 5-10 cm. Moderate SW wind. Treeline high around -10 °C. 

Avalanche Summary

On Monday and Tuesday, natural storm slabs and loose dry avalanches size 1-2 were observed out of NE-SE aspects in the alpine. Explosive triggered storm slabs were observed up to size 2 and ski cut up to size 1.

The persistent slab problem continues to produce sporadic and spotty activity in the South Rockies and nearby regions.

  • On Tuesday just east of the region in the Rockies near Invermere, a size 3.5 (very large) persistent slab avalanche was triggered remotely by a skier on an alpine ridgetop. The resulting crown was 2-3 m deep and the avalanche ran about 1 km to the valley bottom. More details in this MIN report. This and other notable persistent slab avalanches in neighboring regions feature in our latest blog, Photos of recent persistent slab avalanches in the southern interior.

  • On last Friday, explosives triggered a size 2.5 wind slab avalanche that stepped down to the persistent slab layer on a SE aspect near treeline. While recent reports of large persistent slab avalanches have been minimal in the region, neighbouring regions including the Lizard-Flathead have seen some concerning avalanches recently including this one on Sunday.

Snowpack Summary

The region typically received 20-30 cm of new snow from the recent storm. This new storm snow buried a highly wind affected snow surface and widespread facets from the recent cold conditions which may create a weak bond with the new snow. The new snowfall was accompanied by moderate to strong winds at higher elevations and the new storm slabs are expected to be most reactive in wind loaded areas in the alpine. 

The most notable layer of concern in the snowpack is a crust that was formed in early December and is now typically down 70-130 cm. In the past week, we have seen explosive triggered activity on this layer as well as snowpack tests that have shown that the layer remains reactive. Neighbouring regions have seen very large avalanches on this layer over the past week. This layer has created a low likelihood, high consequence scenario which is best managed through conservative terrain choices and disciplined backcountry travel techniques. 

Terrain and Travel

  • Fresh wind slabs will likely form throughout the day, diligently watch for changing conditions.
  • Seek out wind sheltered terrain below treeline where you can avoid wind slabs and find great riding.
  • 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.

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.