Avalanche forecast

South Rockies

Feb 4 – 5, 2021Avalanche Canada
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Avalanche danger

Sat
Sun
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
3 · Considerable
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Highlights

Up to 30 cm of recent storm snow accompanied by strong southwest wind has formed reactive slab avalanches. Natural avalanche activity may taper by Thursday but skier and rider triggering remain likely.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–2

    Moderate to strong northwest wind will continue to redistribute the new snow and build wind slabs in lee terrain features in the alpine and at exposed treeline. It is uncertain how well the transported snow will bond with other old surfaces, for example, hard wind affected layers and pockets of surface hoar or surface facets. If the bond is poor, the wind slabs will be more reactive. 

    Looming cornices may be large and fragile. With respect, give them a wide berth from above and below.

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–2.5

    Up to 30 cm of new snow fell by Wednesday morning. Storm slabs may continue to be reactive on Thursday, especially in areas that received higher snowfall amounts. 

    Loose dry avalanches may occur from steep terrain features.

Confidence

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

Weather Forecast

Thursday: Cloudy with some flurries 3-5 cm. Alpine temperatures near -10 and freezing levels at the valley bottom. Ridgetop winds are strong from the west-northwest.

Friday: Mix of sun and cloud with isolated flurries. Alpine temperature low of -22 with strong ridgetop wind from the West.

Saturday: Mix of sun and cloud. Alpine temperatures low -25 and high -10. Ridgetop wind moderate to strong from the West.

Avalanche Summary

No recent avalanche reports received on Wednesday by 4 pm.  

On Sunday, reports of size 1-1.5 wind slabs were triggered by explosives. Several loose dry avalanches up to size 2 were reported in steep alpine and treeline terrain on the weekend. 

With forecast strong wind, fresh wind slabs, and recent storm slabs will likely remain reactive on Thursday. Loose dry avalanches may occur from steep terrain features.

Snowpack Summary

Up to 30 cm of new snow fell by Wednesday morning. The new snow accompanied by a strong west-northwest wind will likely redistribute some of this snow to leeward slopes and terrain features building fresh storm and wind slabs. The surface snow at lower elevations in the southern part of the region may see a surface crust from the higher freezing levels on Tuesday. This additional snow brings up to 60 cm of storm snow (over the past week) that sits above a plethora of old snow surfaces. In the alpine and at treeline the buried surfaces consist of stiff wind affected snow, surface facets, sastrugi, pockets of soft snow, surface hoar in isolated areas sheltered by the wind, and a sun crust on steep solar aspects. Below 1900 m a thick crust can be found underneath the recent snow. 

A solid mid-pack sits above deeply buried decomposing crust and facet layers near the bottom of the snowpack (80-150 cm deep). Though unreactive under the current conditions, steep rocky slopes and shallow snowpacks should still be carefully assessed and approached with caution.

Terrain and Travel

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Watch for signs of instability like whumpfing, hollow sounds, shooting cracks or recent avalanches.
  • Avoid terrain traps where the consequence of any avalanche could be serious.
  • Be carefull with sluffing in steep terrain, especially above cliffs and terrain traps.
  • Pay attention to cornices and give them a wide berth when traveling on or below ridges.

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