Bulletin d’avalanche

Purcells

Jan 28 – 29, 2012Avalanche Canada
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Archivé · expiré 15 years ago

Danger d’avalanche

Mon
Tue
Alpin
4 · Fort
Limite forestière
4 · Fort
Sous la limite
3 · Marqué
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Problèmes avalancheux

  • Wind Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    1–5
    Expect wind slab development on slopes immediately lee to the S, SW winds. Wind slabs to a half meter in depth are within the realm of reason. Best to give wind affected terrain a miss as it will need a day or two to adjust to this new load.

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    4–7
    Recent avalanche activity indicates that deeply buried weak layers are once again reactive to light loads. A skier, sledder or avalanche running in the storm snow could trigger a large avalanche, especially in steep rocky terrain.

  • Storm Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    1–5
    The weekend storm comes in cool, goes warm, then turns cool again. This will make for, "upside down" snow Sunday morning which will lend to slab development. Watch for cohesive slow moving slabs in sheltered locations Sunday.

Confidence

Poor - Timing, track, or intensity of incoming weather is uncertain on Sunday

Avalanche Summary

Control work in the Dogtooths continues to produce avalanches running to ground on basal facets & depth hoar in high elevation terrain with light loads. Further south, large loads produced very little results at mid elevations with large loads. Friday's winds formed stubborn wind slabs 20 - 30 cm in depth which were largely unreactive to skiers.

Weather Forecast

For better or worse, weather models are far from perfect. They have a particularly tough time with situations like the one we're in now. The models call for rapidly changing freezing levels, strong to extreme winds out of the SW and uncertain precip amounts. My best guess for the Purcells is 15 cm of snow. The big winds will likely get right to work Saturday night out of the SW with sustained strong values, gusting extreme. Freezing levels will spike Sunday and may rise as high as 1800m. Cooling will build in Monday and then Tuesday looks to be fairly dry. This is all fine & good, but I must admit that my confidence in any model is quite low for the short term, so, take this weather forecast with a grain of salt and be ready for rapidly changing conditions.

Snowpack Summary

The Purcell's are one of the more complex & variable snowpacks in the province right now.The region has received 70 - 130 cm of storm snow in the last week. A few shears are persisting in the new snow, but show signs of healing. Winds have been predominantly out of the W, SW, but some stations have reported NW winds in the last 24 hours. I've received obs of surface snow that is untouched by winds, and other obs where winds have produced a wind slab avalanche cycle. It's tough to put a pattern on what's happening out there. The reality is that it's highly variable drainage to drainage.The Friday (Jan.) 13th Surface Hoar is still reactive in compression test, producing moderate sudden planar results.The mid-December surface hoar/facet combo is down around 70 cm on the E side of the range & 230 cm on the west side. I suspect it's still susceptible to human triggering in the shallow snowpack areas.

Régions couvertes