Bulletin d’avalanche

Northwest Inland

Mar 7 – 9, 2012Avalanche Canada
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Archivé · expiré 15 years ago

Danger d’avalanche

Fri
Sat
Alpin
4 · Fort
Limite forestière
3 · Marqué
Sous la limite
3 · Marqué
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Problèmes avalancheux

  • Wind Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    1–4
    Recent variable winds have deposited fresh wind slabs in unusual places, but generally lurking below ridgecrests, behind terrain features and in gullies. Cornices are large and weak and could trigger large wind slabs below.

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible - Likely
    Taille
    3–6
    The persistent weak layer continues to be buried by a few cm each day. Avalanches on this layer have not been reported for a few days, but we feel that it could still be easily triggered by skiers and riders.

Confidence

Fair - Timing, track, or intensity of incoming weather is uncertain for the entire period

Weather Forecast

A series of frontal systems is expected to affect the region throughout the forecast period with at 5-15cm expected each day for Thursday, Friday, and Saturday, with Thursday looking like the warmest and wettest. Strong southerly winds on Thursday should shift to southwesterlies by Friday. Freezing levels around 1000m on Thursday should drop to or near valley bottoms by the weekend.

Avalanche Summary

Recent reports include evidence of a natural avalanche cycle that occurred during intense wind-loading on Sunday afternoon. This includes numerous natural cornice triggered slab avalanches up to Size 3, but mostly in the Size 1-2 range, as well as several Size 2 thin wind slabs. Slope cutting on Monday produced a Size 1-2 storm slab avalanche that failed on an old interface from late February.

Snowpack Summary

Isolated strong and variable winds in exposed treeline and alpine areas has probably resulted in reverse loading, sastrugi, surface crusts, and looming undermined cornices in many areas. While in other areas the 10-15cm of fresh low density snow fell with very little or no wind effect. Recent snowpack tests on a northeast aspect at 1480m gave several resistant planar shears the recent storm snow and two hard resistant planar shears down 37cm and 70cm where the total snowpack depth was 5m. The mid February interface, down around 60cm, is variable and generally consists of a strong melt freeze crust below 1000m. Above that elevation, expect to find buried facets, and/or surface hoar (in more sheltered areas), and/or a sun crust on southern aspects. The surface hoar is not widespread but is responsible for much of the larger avalanches that occurred earlier this week. This layer should be on your radar, as it may be susceptible to rider triggers.

Régions couvertes