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Avalanche Forecast

Archived

Jan 8th, 2022–Jan 9th, 2022

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

Regions

Purcells.

Steady winds will impact loose snow. Be especially mindful around steep, convex openings in the trees and ridge features in the alpine. 

Confidence

Moderate -

Weather Forecast

Saturday night: Mostly cloudy with isolated flurries, up to 5 cm. Moderate to strong SW wind. Treeline low around -8 °C. 

Sunday: A mix of sun and cloud. Moderate SW wind. Treeline high around -5 °C.

Monday: Sunny. Moderate SW wind switching NW. Treeline high around -3 °C.

Tuesday: Sunny. Moderate WSW wind gusting to extreme. Treeline high around -4 °C

Avalanche Summary

On Friday, explosives triggered storm stab avalanches to size 2, on average 20 cm deep. Skiers triggered numerous small (size 1) avalanches. A natural avalanche cycle to size 1.5 occurred Thurs-Fri night with rapid loading of new snow.

On Wednesday, evidence of a natural storm slab avalanche cycle size 1-2 was observed, likely having run during the storm earlier in the week. Wind slabs continued to be reactive near Invermere into Tuesday, up to size 2. By Wednesday, avalanche activity was predominantly loose dry entraining mass to size 1.5-2.

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.

Snowpack Summary

25-50 cm of new snow accumulated by the end of Friday, accompanied by southwesterly wind and warming temperatures. In open terrain and upper elevations, wind developed more reactive deposits around lee and convex features. An accumulated total of 30-70 cm of new and recent snow now sits over variable and potentially weak snow surfaces including widespread facets, wind affected snow, and/or surface hoar up to 3 mm in sheltered areas.

The most notable layer of concern in the snowpack is a crust that was formed in early December and is now down 70-150 cm. Activity on this layer has been sporadic. It has generally been triggered on steep, rocky slopes, with a shallow or thin-to-thick snowpack. 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

  • Seek out sheltered terrain where new snow hasn't been wind-affected.
  • Avoid freshly wind loaded terrain features.
  • Be aware of the potential for large avalanches due to the presence of a deep persistent 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.