Bulletin d’avalanche

South Rockies

Feb 3 – 4, 2021Avalanche Canada
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Archivé · expiré 6 years ago

Danger d’avalanche

Fri
Sat
Alpin
3 · Marqué
Limite forestière
3 · Marqué
Sous la limite
2 · Modéré
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Points saillants

New snow and strong wind from the southwest will build touchy wind slabs in leeward terrain features. Fresh storm slabs may be reactive to rider triggers in sheltered terrain, especially where they sit above a buried surface hoar or crust interface.

Problèmes avalancheux

  • Wind Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    1–2

    Moderate to strong southwest 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

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    1–2

    Storm slabs may be reactive especially in areas that received higher snowfall amounts. 

Confidence

Moderate - Forecast snowfall amounts are uncertain.

Weather Forecast

Tuesday Night: Snow amounts 5 cm. Ridgetop wind strong from the southwest. Alpine temperatures near -7 and freezing levels at valley bottom.

Wednesday: Mix of sun and cloud. Ridgetop wind 25-40 KM/hr from the West. Alpine temperatures near -6 and freezing levels at valley bottom.

Thursday: Mix of sun and cloud with flurries. Ridgetop wind light to moderate to strong from the West. Alpine temperatures near -10 and freezing levels at valley bottom.

Friday: Light snow up to 10 cm. Alpine temperatures near -26 for the low and -10 for the high. Ridgetop wind generally light with some strong gusts from the West and freezing levels at valley bottom.

Avalanche Summary

No new avalanches were reported on Tuesday. 

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 the forecast snow and strong wind, wind and storm slabs will likley remain reactive on Wednesday.

Snowpack Summary

Up to 10 cm of new snow fell by Tuesday afternoon. The new snow accompanied by a strong southwest 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 may be moist due to rain and higher freezing levels and likely form a crust by Wednesday. This additional snow brings up to 40 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.
  • Pay attention to cornices and give them a wide berth when traveling on or below ridges.
  • Avoid terrain traps where the consequence of any avalanche could be serious.

Régions couvertes