Bollettino valanghe

Northwest Inland

Jan 30 – 31, 2015Avalanche Canada
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Archiviato · scaduto 12 years ago

Pericolo valanghe

Sun
Mon
Alta quota
3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
2 · Moderato

In sintesi

Don't let the clear weather on Saturday lure you into aggressive terrain. Persistent weak layers exist with the potential for large and destructive avalanches. As solar radiation increases, so will the Avalanche Danger.

Problemi valanghivi

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    2–4
    Persistent weak layers, buried in the middle of January, may "wake-up" in response to recent storm loading. These layers are buried up to a metre below the surface, and can surprise with nasty consequences.
  • Storm Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible - Likely
    Dimensione
    1–3
    Storm accumulations from Friday will likely remain sensitive to human triggering. Expect increased reactivity in wind-exposed terrain. A smaller surface avalanche in motion may also trigger a larger avalanche on deeper layers.
  • Deep Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Unlikely - Possible
    Dimensione
    3–6
    Although less likely to trigger, recent avalanche activity suggests weak layers buried at the beginning of the winter should still be our radar. Avalanches at this interface may reach the end of their run-out zones.

Confidence

Fair - Due to the number of field observations

Weather Forecast

Friday's storm system will dissipate on Saturday as a weak ridge develops. On Sunday and Monday, the ridge will flatten-out allowing for a series of pacific system to impact the region. Saturday: Generally clear skies with valley fog / Light northwest winds / Freezing level at valley bottom Sunday: Up to 10cm of new snow / Moderate southwest winds / Freezing level at valley bottom Overnight Sunday and Monday: Up to 15cm of new snow Moderate southwest winds / Freezing level at valley bottom

Avalanche Summary

There were a few close calls last weekend and into Tuesday. On Sunday in the Hankin area, a skier accidentally triggered a size 2.5 avalanche which resulted in a full burial and minor injuries. The avalanche was reported to have occurred on a wind-loaded, north-facing slope. The avalanche initially failed on the January crust/surface hoar combo, and then stepped-down to the November crust and basal facets. On the same day in the Sinclair area, a snowmobile may have been the trigger for a size 3 avalanche. The avalanche had a crown between 1 and 2 metres, and propagated up to 200 metres wide. It occurred on a wind-loaded, north-facing alpine slope and may have failed on the November crust facet combo. On Tuesday 27th, a couple of small skier-triggered avalanches were reported. One occurred on a steep roll over at lower treeline elevation and ran on the mid-January layer. The other was a small section of wind slab that pulled off a ridge line in wind affected terrain. In the wake storm loading on Friday, I would expect ongoing storm slab activity (especially in wind-exposed terrain) with the potential to trigger deeper, more destructive persistent layers.

Snowpack Summary

Moderate to heavy snowfall and strong southwest winds have built deep and dense storm slabs. These storm slabs are expected to be most reactive in wind-exposed, upper elevation terrain. Below treeline, new snow accumulations may overlie a hard, re-frozen crust. A rain crust and/or surface hoar layer buried mid-January may be found at variable depths between 60- 100cm below the surface. This persistent weakness has been reactive with recent storm loading. Near the base of the snowpack is the crust-facet combination buried in November. This deep persistent weakness seems to have "woken-up" in some terrain in response to warming and heavy loading from wind and snow.

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