Lawinenlagebericht

Sea To Sky

Mar 11 – 12, 2012Avalanche Canada
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Lawinengefahr

Tue
Wed
Hochgebirge
4 · Gross
Waldgrenze
4 · Gross
Unterhalb
4 · Gross
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Kernpunkte

Monday's danger ratings assume that a major storm will arrive in the morning. The timing of this system is uncertain and danger ratings may be a bit too high if the storm arrives later.

Lawinenprobleme

  • Wind Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Likely - Very Likely
    Größe
    1–6
    Strong winds continue to create wind slabs below ridges, behind terrain features and in gullies. These are becoming deeper and heavier by the day, and are expected to cause large natural avalanches.

  • Persistent Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible - Likely
    Größe
    4–8
    Heavy loading is expected to reawaken a persistent weakness in the upper snowpack. The potential for remote triggering, step down avalanches, and wide propagations makes this persistent slab problem particularly tricky to manage.

  • Storm Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Likely - Very Likely
    Größe
    2–6
    Storm slabs are building with successive weather systems. Touchy weaknesses within and under the recent storm snow have been reported. Cohesionless low-density snow overlying a crust can also produce large loose-snow avalanches.

Confidence

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

Weather Forecast

Batten down the hatches!Monday: A deep Pacific low spreads moderate to heavy snow to valley floor (25-30cm). Severe winds and thunderstorms are possible. The timing and intensity of this system are uncertain.Tuesday: Light convective snow. Moderate winds, gusty at times. Freezing level around 600m.Wednesday: The next low pressure system arrives with moderate to heavy snow, strong south-westerly winds and freezing level rising slightly.

Avalanche Summary

It's been an active week for avalanche activity. Saturday's storm snow was triggered naturally, by skiers and by explosives to size 2 on a variety of slopes. Many occurred on wind-loaded north-east to north-west aspects. Two skier involvements were reported on north/north-west aspects at 2100m. Earlier in the week, snowmobilers remotely triggered avalanches from 200m below the fracture line. There was an avalanche fatality at Grizzly Lake on Powder Mountain on Tuesday involving a snowmobiler. The avalanche occurred on an east aspect near 2000m. The slab was 80cm-150cm thick and 525m wide and failed on the mid-February persistent weakness. An unnervingly large natural avalanche cycle occurred last weekend, with slabs up to size 4.5 propagating 2-3km along ridgelines and stepping down to the mid-February layer. Similar avalanches are possible as storm loading continues this week.

Snowpack Summary

Stormy conditions are creating ever-deeper wind slabs and storm slabs. These overlie various old surfaces including crusts, moist snow, old wind slabs and old storm slabs. Reports from the field suggest variable reactivity in the recent storm snow. A key concern is the potential for a storm- or wind-slab to step down and trigger deeper weaknesses, formed in mid-February, which are still producing clean and fast shears in snowpack tests. Very large avalanches are possible, which could be remote-triggered, triggered mid-slope, and/or propagate into low-angled terrain.

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