Lawinenlagebericht

Kootenay Boundary

Apr 6 – 7, 2012Avalanche Canada
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Lawinengefahr

Sun
Mon
Hochgebirge
3 · Erheblich
Waldgrenze
3 · Erheblich
Unterhalb
2 · Mässig
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Lawinenprobleme

  • Cornices

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Likely
    Größe
    3–7
    Cornices have grown large & unruly. Cornices receiving direct sun will eventually grow weak & there is potential for cornice fall to initiate deep persistent slab avalanches on underlying slopes. Pay attention to what's happening above you.

  • Storm Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Likely
    Größe
    2–5
    Two layers to watch: April 3rd, down 30 cm & Mar. 26, down 100 cm. I'd be wary of triggering the deeper layer on steep unsupported slopes, especially in places where the snowpack goes from thick to thin; near ridge crests and rock outcroppings.

  • Loose Wet

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Likely - Very Likely
    Größe
    1–5
    Periods of sun are expected Saturday & the new snow will likely react to the strong solar input, producing loose snow avalanches, with the potential for deeper slab avalanches on slopes that bake all day under the strong spring sun.

Confidence

Fair - Timing or intensity of solar radiation is uncertain for the entire period

Weather Forecast

A stagnant weather pattern dominated by a ridge of high pressure brings increasingly sunny periods with benign convective cloud over the holiday weekend. Saturday: Freezing level starts at the surface, climbs to 1900 m, then returns to the surface overnight. Ridge top winds light out of the SW. Sunday: Flow switches from north to south late in the day allowing freezing levels to climb as high as 2000 m. Winds moderate East, switching S, SE Sunday night. Monday: Winds light S. Freezing level starts around 1000 m, climbs to 2000 m in the afternoon.

Avalanche Summary

Control work Thursday morning produced dry avalanches from size 1 - 2. Temps warmed up in the afternoon which produced a widespread solar induced cycle to size 2 on SW, S & SE facing slopes. Clear skies allowed for good visibility; one operator in the region observed evidence of an extensive natural cycle from April 3rd on S/SE aspects at and above treeline to size 3, failing on the March 26th crust/facet interface.

Snowpack Summary

The snow surface was introduced to the strong spring sun Thursday afternoon which left a crust in place on solar aspects, those that face SW, S & SE. Around 30 cm of snow fell Wednesday accompanied by moderate southwest winds which brings total snowfall since March 26th to 120 cm. This snow rests on a suncrust on solar aspects and a melt freeze crust on non solar aspects below 2000m. On N aspects, shears within the upper storm snow are tightening with the persistent warm temperatures, although a reactive layer down 40-50cm remains. The March 26 interface consists of a melt/freeze crust down around 100cm, on all aspects except true north treeline and alpine, where small surface hoar (5mm) is present in sheltered places. The bond at this interface is gaining strength, with lingering concerns on true south aspects where the crust is thickest and where the surface hoar lurks. At lower elevations, the consistent high freezing levels have kept the new snow heavy and moist. The deep, persistent early February surface hoar lingers in the snowpack giving sudden results in testing. Concern remains with heavy triggers (cornice), step down avalanches and rapid loading from intense precipitation, strong winds or sun.

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