Bulletin d’avalanche

South Coast

Jan 5 – 6, 2015Avalanche Canada
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Archivé · expiré 12 years ago

Danger d’avalanche

Wed
Thu
Alpin
4 · Fort
Limite forestière
4 · Fort
Sous la limite
3 · Marqué
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Points saillants

Storm conditions Monday overnight means High hazard for Tuesday. Be conservative in your terrain choices and give the snowpack time to stabilize.

Problèmes avalancheux

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    2–6
    Heavy loading from new snow, wind, and rain could overload persistent weaknesses in the top 1 m of the snowpack, leading to very large and destructive avalanches.

  • Storm Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Very Likely
    Taille
    2–5
    Thick, dense storm slabs have formed during the recent storm. Strong winds have formed wind slabs in exposed terrain. Rain at the end of the storm will also add load and increasing the instability of the slab. Cornices will become weak with warming.

  • Loose Wet

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    1–3
    Rain at lower elevations will destabilize the upper snowpack. Wet sluffs from steep terrain may be able to trigger storm slabs.

Confidence

Fair - Timing, track, or intensity of incoming weather system is uncertain

Weather Forecast

The warm front brings heavy precipitation and strong-to-extreme winds overnight Monday and early Tuesday. 20-30mm of precipitation are expected with freezing levels gradually rising from around 1500m to around 2500m. Storm conditions should ease on Tuesday morning but freezing levels will continue to rise to around 3000m. Wednesday is expected to be dry with increasing sun during the day. Freezing levels will stay around 3000m and alpine winds are expected to be light. Thursday looks like the warmest day with freezing levels reaching as high as 3500m. Dry and mainly sunny conditions are expected. A cooling trend is expected into the weekend.

Avalanche Summary

On Sunday, widespread natural and skier triggered activity was reported.  However, this activity was limited to size 1.5 soft slabs.  As the new snow accumulates, this widespread natural activity is expected to continue but the size will increase.  By the end of the storm, storm slabs are expected to result in avalanches to size 3.  If the avalanche steps down to a buried weak layer, avalanches could be even bigger.

Snowpack Summary

The storm snow sits on a previous variable snow surface that included wind affected surfaces (crust, hard and soft slabs), a freezing rain crust or sun crust, and surface hoar or sugary facets in sheltered shady terrain. How well the new snow bonds to this surface is the question. This storm is starting cold and will finish much warmer, meaning that the new storm snow will be more dense on top - a good recipe for slabs. Cornices will become weak with warming. Below the new snow we might find the mid-December surface hoar or crust/facet weak layers. These were buried between 40 and 80 cm deep on average. The surface hoar layer may be found in sheltered shady areas at and below treeline, while the crust/facet layer could be more widespread but also more variable. Reports suggest is could be between 0 and 120 cm deep depending on exposure to wind. Heavy loading in the coming days could trigger these weaknesses creating very large avalanches.

Régions couvertes