Bulletin d’avalanche

South Rockies

Jan 22 – 23, 2020Avalanche Canada
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Archivé · expiré 7 years ago

Danger d’avalanche

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

Use extra caution in avalanche terrain when air temperatures rise above zero, especially for the first time. Also be alert to slopes getting direct sun, if it comes out Wednesday. These two factors can make slabs more sensitive to triggering.

Problèmes avalancheux

  • Wind Slabs

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

    Strong westerly winds have blown recent snow into stiff windslabs in lee features at alpine and treeline. Human triggering of windslabs is possible.

  • Deep Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Unlikely
    Taille
    2–3

    As temperatures trend warmer and freezing levels rise, there is potential for the deep basal weak layers to become active. Deep persistent slab avalanches on these layers are most likely to be triggered from shallow snowpack areas near rocky outcroppings.

Terrain and Travel

  • Extra caution for areas experiencing rapidly warming temperatures for the first time.
  • Minimize exposure to sun-exposed slopes when the solar radiation is strong.
  • Be careful with wind slabs, especially in steep, unsupported and/or convex terrain features.
  • Avoid steep, rocky, and wind effected areas where triggering slabs is more likely.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.

Confidence

Moderate - Uncertainty is due to difficult to forecast freezing levels.

Weather Forecast

The freezing level spikes over the next few days will be more pronounced the farther south you go in the region.

Tuesday night: Overcast with isolated flurries bringing up to 5 cm of new snow. Moderate southwest winds. Alpine low -6 C. Freezing level dropping to around 1000 m.

Wednesday: Broken cloud with isolated flurries bringing a trace of new snow. Moderate west to southwest winds. Alpine high -5 C. Freezing level around 1300 m.

Thursday: Mix of sun and cloud with isolated flurries bringing a trace of new snow. Moderate west to southwest winds. Alpine high -1 C. Freezing level rising to 1800 m.

Friday: Mix of sun and cloud with isolated flurries bringing a trace of new snow. Moderate west to southwest winds. Alpine high +1 C. Freezing level around 2000 m.

Avalanche Summary

On Monday we received reports of natural and explosive triggered windslab avalanches size 1.5-2.

On Thursday a natural size 2 wind slab stepped down to the deep persistent basal facets below a rock band, details here. 

Snowpack Summary

Recent strong westerly winds have formed stiff windslabs low in alpine lees. A crust can be found at lower elevations and on solar aspects due to recent daytime warming and sun exposure. 

A well consolidated mid-snowpack overlies a generally weak basal snowpack. The bottom 10-20 cm of the snowpack consists of facets and deteriorating crusts. There is potential for this deep persistent layer to reawaken in the warm alpine temperatures later in the week.

Régions couvertes