Bollettino valanghe

Central Cascades

Central Oregon Avalanche Center
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Pericolo valanghe

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

Triggering a slab avalanche in wind deposited snow will be likely near and above treeline on Saturday. Triggering slab avalanches in the recent storm snow will be possible anywhere the snow has not been scoured away by the wind. If you observe signs of unstable snow, cracking, previous avalanches, or if you have uncertainty in the stability of the snowpack, increase your safety margin by sticking to slopes less than 30 degrees steep. 

Problemi valanghivi

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    1–2.5

    On Friday I observed significant blowing snow near treeline.... that snow always ends up somewhere. With a few inches new snow overnight and a large reservoir of snow available for transport, wind slabs will continue to build overnight before the wind backs off.

    Wind slabs tend to stabalize after a few days but they are still in the realm of triggering.

    Avalanches will range from small to large. Be especially cautious where triggering even a small avalanche on a steep slope or above terrain traps can lead to a bad outcome.

    Watch for signs of wind deposited snow in clearings and areas with sparse trees even below treeline. Remember burned areas and slopes with dead trees can experience a big wind affect and get a lot of wind drifted snow. 

    Wind can deposit snow 5 times deeper or more than the snow that fell out of the sky. Use visual clues to identify where wind slabs have formed. Monitor the depth of wind deposited snow. Deeper wind slabs can result in larger avalanches. Wind slabs typically form below ridgetops, high points, and around any features that catch wind blown snow. 

    (3/10/2023)

    Cracking in fresh wind slab on a small test slope. East aspect.

    Photo: Aaron Hartz

  • Storm Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–2

    Storm slabs will be trending toward more stubborn to trigger but keep them in mind for one more day. Late in the afternoon on Friday, I observed cracking in the storm slabs on steep convex rolls and storm slabs were failing easily during hand shear tests (down 45 cm/18")

    Triggering a storm slab will be possible on slopes that have not been scoured by the wind. These avalanches will be more likely in steep, convex, and rolling terrain but can occur anywhere the slope is steep enough for snow to move. 

    Utilize small and safe test slopes to look for signs of cracking or slabs releasing to evaluate this problem.

  • Cornices

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–2

    On Saturday as clouds clear out, the visibility will improve and give backcountry travelers the opportunity to venture into the higher elevations. Be cautious when approaching ridge tops where cornices have formed over lee slopes. Fresh cornices can be fragile, break easily, and falling cornice debris can trigger slides on the slope below. Stepping out onto a cornice could result in a break, leading to a fall onto the slope below along with large chunks of snow.

Avalanche Discussion

We had a whopper of a storm with 20-30" of new snow at different elevations. Storm related avalanche problems tend to stabalize after a few days but can take longer in some cases. The day after a big storm, the problems can still be real.

Lower elevation slopes in the direct sun may warm up enough to bring on the wet loose avalanche problem. Monitor the surface snow as the day warms up. If you feel the snow becoming wet, heavy, or slushy, be aware of triggering wet loose avalanches. Roller balls and pinwheels are precursors to this problem. 

 

Regioni coperte