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Avalanche Forecast

Archived

Jan 11th, 2022–Jan 12th, 2022

Alpine
Natural and human triggered avalanches likely.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches possible, human triggered probable.
Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
Below Treeline
Natural avalanches possible, human triggered probable.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches possible, human triggered probable.

Regions

Lizard-Flathead.

Up to 35 cm by the end of the day Wednesday combined with wind and the freezing level rising to 1800 m bring the avalanche hazard to HIGH in the alpine. There is uncertainty whether deeper weak layers will become more reactive, resulting in large and destructive avalanches.

Confidence

Moderate - Uncertainty is due to how buried persistent weak layers will react with the forecast incoming weather.

Weather Forecast

Tuesday night: Cloudy, 10-20 cm new snow, moderate to strong southwest wind, treeline low around -3 °C, freezing level around 1400 m.

Wednesday: Cloudy, 5-10 cm new snow and rain at lower elevations, moderate southwest wind, treeline high around +1 °C, freezing level rising to around 1800 m.

Thursday: Sunny with increasing cloud coverage, up to 3 cm new snow, moderate southwest wind, treeline high around +1 °C, freezing level rising to 2200 m.

Friday: Mix of sun and cloud, trace of new snow, light southwest wind, treeline high around -2 °C, freezing level around 1400 m.

Avalanche Summary

On Monday, now new avalanches were reported.

On Sunday, a few natural cornice failures resulting in size 2.5 avalanches were observed as well as a natural size 2 slab avalanche. 

On Saturday, storm slab avalanches up to size 2.5 were triggered by explosives. Overnight, a large (size 3.5) natural storm slab avalanche released and a large (size 2.5) cornice failure occurred. 

On Friday, storm slab avalanches released naturally up to size 2.5. Explosives triggered storm slabs to size 2.5, and skiers triggered avalanches to size 2. A large (size 2) natural cornice failure was reported likely having failed in the overnight storm.

The persistent slab problem has produced sporadic and spotty activity in the Lizard-Flathead and nearby regions. 

  • On Monday, a large size 3 deep persistent slab released naturally in the neighbouring Waterton National Park. The avalanche was more than 2 m deep.
  • On Sunday, a very large (size 4) persistent slab avalanche that released naturally in the neighbouring Waterton National Park was observed. The avalanche released at an elevation of 2000 m on an E-NE aspect. Large avalanches (up to size 3.5) were reported in the Fernie area with the early December layer as suspected bedsurface. The avalanches likely ran during the storm on Friday or Saturday.
  • Last Wednesday, two size 3 persistent slab avalanches were reported. They released at an elevation of 1800 m and 2000 m on an E aspect and were 2 m deep. Most likely they released during the storm before the New Year. 
  • Last week on Sunday, a size 2.5 persistent slab avalanche was triggered on an E aspect at treeline. This avalanche is detailed in a MIN post and features in our latest blog post, Photos of recent persistent slab avalanches in the southern interior.

Snowpack Summary

The recent storm snow totals 40-50 cm. In open terrain and upper elevations, wind developed more reactive deposits around lee and convex features. This recent snow covered a hard, faceted snow surface which formed during cold temperatures and may take a little time to bond. 

The most notable layer of concern in the snowpack is a crust that was formed in early December and is now down 100-270 cm. Activity on this layer has been sporadic, the most recent persistent slab avalanche in the region was reported on January 9. 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

  • Extra caution for areas experiencing rapidly warming temperatures for the first time.
  • Storm slabs in motion may step down to deeper layers resulting in large avalanches.
  • 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.
  • Caution around slopes that are exposed to cornices overhead.

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.