Boletín de aludes

South Rockies

Jan 12 – 13, 2022Avalanche Canada
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Archivado · caducó 5 years ago

Peligro de aludes

Fri
Sat
Alta montaña
4 · Fuerte
Límite del bosque
3 · Notable
Bajo el límite
3 · Notable
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Lo esencial

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. 

Problemas de aludes

  • Wind Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Likely
    Tamaño
    1.5–2.5

    Moderate to strong southwest wind continues to redistribute the recent new snow. More reactive deposits will be found on convex rolls and leeward terrain below ridges. Wind slabs might have formed lower down slope than expected with the strong wind. The recent snow may overlie a weak interface which could result in deeper and touchier than expected slabs.

    It is uncertain how the forecast warm temperatures will affect the snowpack. Small avalanches may step down to deeper weak layers and result in large and destructive avalanches. 

  • Persistent Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Possible
    Tamaño
    2–3.5

    A persistent slab problem formed by a crust down 80-150 cm has created a low likelihood, high consequence scenario that is difficult to forecast. There has been an increase of avalanche reports on this layer since the past weekend. It is uncertain how the forecast warm temperatures will affect the snowpack and if we will see more activity on this layer during the warm period. 

    Avoid likely trigger spots such as steep, rocky slopes with a shallow or thin to thick snowpack. Large additional loads like small avalanches or failed cornices can trigger deeper weak layers. The same feature or path can slide repeatedly when the persistent weak layer is reloaded with new snow. 

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.

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