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Avalanche Forecast

Archived

Jan 7th, 2022–Jan 8th, 2022

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

Regions

Purcells.

Expect to find deeper and more reactive deposits in lee terrain. Be especially mindful around steep, convex openings and ridge features.

Confidence

Moderate - Uncertainty is due to the speed, direction, or duration of the wind and its effect on the snowpack.

Weather Forecast

Friday night: Tapering flurries, up to 10 cm overnight. Strong decreasing to moderate W wind. Treeline low around -20 °C.

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

Sunday: A mix of sun and cloud. Moderate SW wind. Treeline high around -4 °C.

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

Avalanche Summary

Few avalanches were reported on Thursday, however a natural avalanche cycle likely occurred sometime between Thursday and Friday 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

20-50 cm of new snow accumulated by the end of Friday was accompanied by southwesterly wind and warming temperatures. An accumulated total of 40-80 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.
  • Be aware of the potential for large avalanches due to the presence of a deep persistent slab.

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.