Bulletin d’avalanche

South Coast Inland

Feb 4 – 5, 2020Avalanche Canada
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Archivé · expiré 7 years ago

Danger d’avalanche

Thu
Fri
Alpin
3 · Marqué
Limite forestière
3 · Marqué
Sous la limite
3 · Marqué
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Points saillants

Posted avalanche danger ratings are for the north of the region where a deep persistent avalanche problem continues to be a concern. Avalanche danger in the south of the region (Coquihalla and Manning areas) is MODERATE.

Problèmes avalancheux

  • Wind Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible - Likely
    Taille
    1–2.5

    Strong to extreme winds during last weekend's storm have created thick deposits of wind loaded snow in lee terrain features.

  • Deep Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible - Likely
    Taille
    2–4

    Deep weaknesses near the bottom of the snowpack have been failing under recently applied snow loads, resulting in very large, destructive avalanches. Many of these avalanches have run to valley bottom; hence posing a hazard to all elevations. These layers do not pose an avalanche problem in the south half of the region.

Confidence

Moderate - Uncertainty is due to extremely variable snowpack conditions reported through the region. Uncertainty is due to the fact that deep persistent slabs are particularly difficult to forecast.

Weather Forecast

Monday Night: Cloudy with clear periods. Light to moderate southwest wind. Alpine high -9 C.

Tuesday: Scattered flurries. Moderate to strong southwest and west wind. Alpine high -8 C.

Wednesday: Flurries, accumulation 5-10 cm. Strong west wind. Alpine high -4 C. Freezing level 500 m.

Thursday: Flurries, accumulation 5-15 cm. Moderate southwest wind. Alpine high -2 C. Freezing level 700 m.

Avalanche Summary

Numerous size 3-4 deep persistent slab avalanches were reported Saturday in north parts of the region including the Lillooet River valley north of Pemberton and near Goldbridge. Start zones included all aspects 1900-2300 m and avalanches ran to valley bottom, taking out mature timber and blocking waterways. 

Explosive work conducted Saturday also produced deep persistent size 2-3 in these areas as well as in the Duffey. In some cases, these large touchy slabs were triggered not by detonation, but as the explosive product landed on the slope.

A widespread size 2-3 natural storm slab cycle was observed in most areas toward the tail end of the storm Saturday.

Snowpack Summary

Above 1800 m, weekend storm totals for the north of the region are in the range of 30-50 cm, while the Coquihalla received around 100 cm and the Manning Park area received around 35 cm. Extreme southwest wind during the storm has scoured windward aspects, formed deep loaded pockets in alpine lees and contributed to rapid cornice growth. Below 1800 m, snow overlies a crust and tapers with elevation.

In the north part of the region (ie. Goldbridge/Duffey/Hurley), a few deep instabilities exist in the snowpack, including a weak basal facet crust complex. This has been the failure plane in ongoing reports of very large, deep persistent avalanches.

The south of the region, including the Coquihalla and Manning areas, currently have no concerns about deeply buried weak layers.

Terrain and Travel

  • Be especially cautious as you transition into wind affected terrain.
  • Make conservative terrain choices and avoid overhead hazard.
  • Avoid the runout zones of avalanche paths. Very large avalanches have been running full path.
  • Use extra caution around cornices: they are large, fragile, and can trigger slabs on slopes below.

Régions couvertes