Lawinenlagebericht

South Rockies

Jan 13 – 14, 2022Avalanche Canada
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Archiviert · abgelaufen 5 years ago

Lawinengefahr

Sat
Sun
Hochgebirge
4 · Gross
Waldgrenze
4 · Gross
Unterhalb
3 · Erheblich
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Kernpunkte

Avalanche conditions remain very dangerous with high freezing levels and a persistent weak layer in the snowpack.

Lawinenprobleme

  • Wind Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Likely
    Größe
    1.5–2.5

    Moderate to strong westerly 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. 

  • Cornices

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Likely
    Größe
    2–3

    Cornices are reactive to human traffic with the warm temperatures and natural cornice falls become more likely. Large cornice falls are dangerous on their own. 

    A failed cornice can trigger buried persistent weak layers and result in very large and destructive avalanches. 

  • Persistent Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    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 cornice falls 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

Wednesday night: Mostly cloudy, trace of new snow, moderate southwest wind, treeline low around -1 °C, freezing level around 2200 m.

Thursday: Mostly sunny, moderate to strong westerly wind, treeline high around +2 °C, freezing level around 2200 m.

Friday: Mostly sunny, up to 5 cm new snow, light westerly wind, treeline high around -2 °C, freezing level around 1400 m.

Saturday: Mix of sun and cloud, trace of new snow, moderate southwest wind, treeline high around -2 °C, freezing level around 1500 m.

Avalanche Summary

By the time of writing on Wednesday, a large cornice fall of size 3 was observed, as well as natural wind slabs up to size 2 in the alpine. 

On Tuesday, skiers triggered several small size 1 wind slabs.

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

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 still 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

  • Minimize overhead exposure; avalanches triggered by warming or cornice fall may be large and destructive.
  • 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.

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