Bulletin d’avalanche

Selkirk Mountains

Idaho Panhandle Avalanche Center
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Danger d’avalanche

Wed
Alpin
3 · Marqué
Limite forestière
3 · Marqué
Sous la limite
2 · Modéré
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Périmé — ce bulletin a expiré 4 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

Heavy snow and strong winds will create dangerous avalanche conditions. Human triggered avalanches are likely in steep alpine areas, especially on wind loaded slopes.  A conservative plan today will help manage the risk. You can best navigate the uncertainty by avoiding all steep slopes and run-out zones. 

Problèmes avalancheux

  • Storm Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    1–2

    Storm snow is quickly adding up across the zone. The storm's prevailing winds are out of the SW and look to favor the southern end of the Cabinets over the Selkirks and Purcells. Winds are forecasted to flip mid-day today, to come out of the E-NE. Expect to see the air temperature drop when that happens. Rapid loading rates of new snow and gusty winds are two classic red flags. Both of these flags have occurred overnight and will continue into today. Recent avalanches, cracking or collapsing are the third and fouth red flags to watch out for today. Your safest bet is avoid being on or under slopes above 30 degrees.

  • Wind Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    1–2

    A variety of wind slabs exist in the snowpack. Old wind slabs will be effected by the weight of new snow, pushing them closer to a trigger point. It's uncertain how much weight is needed to induce failure, but it's best to not test it today.  Old wind slabs can be found on all aspect above treeline. New wind slabs will present in a variety of thicknesses and stiffnesses, and could grow quite large with the forecasted winds.  Strong, cohesive wind slabs can propagate long distances across uniform slopes. The most likely place to see dangerous wind slabs are steep, leeward slopes just below ridgelines and cornices.

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    1–2

    The weight of new snow, which arrives today will put added stress on the PWL's inching it closer to a failure point. Multiple persistent weak layers (PWL) can be found in the upper portion of the snowpack; however, upon testing, they remain resistant to failure. The PWL's can be found in some variety, on most aspects, and at all elevations. Weak snow crystals, at the Lucky Friday crust have developed above and below the crust. The lucky Friday crust can be found about 24-30 inches below the snow surface. The further north you go, the more unlikely it is that you'll find the ' Lucky Friday' crust, but it's pretty easy to find in the southern Cabinet and Selkirk mountains.  

Avalanche Discussion

Yesterday we sledded and toured in the Selkirks Snow Creek drainage before the main course of the storm rolled in the afternoon. In gaining observations for how this new storm snow interface may form we were particularly interested in snow surface variation and air and snow temperatures.

Another 6-12  inches of snow forecasted today along with strong wind at upper elevations will create reactive snow on all aspects at treeline and above.  While generally challenging,  travel through the mountains in these conditions warrants additional caution, and avoidance of avalanche terrain is recommended until the new snow has time to settle and bond to the surface.  Looking ahead, bitter cold temperatures and northeast winds are forecasted to arrive this afternoon and persist into Wednesday.    

Current and forecasted snowfall and wind amounts vary across the forecast zone. Uncertainty lies not just within these variables, but also how touchy or reactive (the sensitivity of) these variables are today. Yet, as the storm progresses, the sensitivity of storm slabs will progress towards instability. Two main decision making factors come to mind right now. 1. Remember instability is highest during and right after storm events. 2. The  uncertainty associated with rapidly changing conditions. Uncertainty today will be best managed by conservative decision making. Be patience, and give the snowpack a couple days to settle down.  If you venture out today, your best tool will be slope angle. Stay away from slopes over 30 degrees and out of runout zones.

Régions couvertes