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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

South Rockies.

The freezing level rising to 2100 m and strong wind drive 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: Mostly cloudy, up to 3 cm new snow, strong southwest wind, treeline low around -5 °C, freezing level around 1800 m. 

Wednesday: Mostly cloudy with flurries, trace of new snow, moderate to strong southwest wind, treeline high around +2 °C, freezing level rising to 2100 m.

Thursday: Mostly sunny, trace of new snow, moderate southwest wind, treeline high around +2 °C, freezing level around 2300 m.

Friday: Mix of sun and cloud, trace of new snow, light westerly wind, treeline high around -2 °C, freezing level around 1500 m.

Avalanche Summary

On Monday, no new avalanches were reported. 

On Sunday, a few small (up to size 1.5) wind slab avalanches were triggered by skiers and explosives.

On Friday, explosives and skiers easily triggered storm slab avalanches to size 1.5.

The persistent slab problem has produced sporadic and spotty activity in the South Rockies and nearby regions. The activity increased over the past weekend. 

  • 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.
  • On Saturday, Jan 8, explosives triggered a very large (size 4) deep persistent slab avalanche at 2100 m on a SE aspect. The avalanche failed 1-2 m deep on the early December layer. 
  • On Friday, a large (size 2.5) natural deep persistent slab avalanche released in the west of the region and was reported in this MIN post.
  • The last activity before that occurred on Dec 31, when explosives triggered a size 2.5 wind slab avalanche that stepped down to the persistent weak layer on a SE aspect near treeline. 

A few recent notables from surrounding regions feature in our latest blog, Photos of recent persistent slab avalanches in the southern interior.

Snowpack Summary

The recent storm snow totals 40-70 cm. Strong to extreme southwest winds have developed reactive deposits around convex and lee 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 typically down 80-150 cm. Activity on this layer has been sporadic, the most recent persistent slab avalanche in the region was on Saturday, January 8. This layer has created a tricky 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.
  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • 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

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.