Bollettino valanghe

Central Cascades

Central Oregon Avalanche Center
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Pericolo valanghe

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

Avalanche danger will increase throughout the day Wednesday as we receive new snow with Extreme winds.  Avalanches could be large in wind blown snow on east slopes near and above treeline.   As the snow accumulates on Wednesday there is also the potential for small avalanches below treeline.  This new snow may be falling on surface hoar that was observed on Tuesday, so avalanches could propogate farther and be easier to trigger than you might otherwise expect.   Very large avalanches on deep weak layers are unlikley but remain a concern.  Avoid steep large slopes and unsupported, relatively shallow slopes.

Problemi valanghivi

  • Wind Slabs

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

    Wind slab avalanches will be likely on Wednesday on any slopes where the wind is blowing the new snow to.  The size of these wind slabs will be proportional to the amount of new snow that we have received.  Wind deposited snow can be 3-5 times as deep as the snow that has fallen from the sky.  The forecast for the next 24 hours calls for Extreme winds from the west.  Often when we have Extreme winds we see unusual loading patterns and sometimes Wind Slabs can develop further down slope than is typical, and even in open glades below treeline.  Watch for unusually deep drifts of snow and for more consolidated surface snow as good clues.  Wind slabs may be touchier and propogate further if they overlay surface hoar from Tuesday.

  • Storm Slabs

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

    On Tuesday I observed surface hoar from Monday night.  Where this surface hoar is buried by the new snow there is the potential for Storm Slab avalanches.  The size of these avalanches will be directly porportional to the amount of new snow that has fallen, and thus will increase throughout the day.  The best test for Storm Slab instabilities will be looking for small avalanches, cracking or even slabby snow on small test slopes (small, steep, convex rolls).  It may also help to remind yourself where surface hoar tends to form (slopes that are Cold, Clear, and Calm), and where it is best preserved (colder slopes that are sheltered from the wind and sun).

  • Deep Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Unlikely
    Dimensione
    2–3

    Triggering a Deep Persistent Slab is unlikely but would be catastrophic.  We have seen some very large avalanches in the last week, specifically the two on Middle Sister.  The layers that we are worried about include burried surface hoar and facets that exist approx 125 - 175 cm. beneath the surface where the crusts from early in the month can be found.  It is increasingly difficult to assess these layers and the best strategy for negotiating a Deep Slab is increasing your margin of safety when riding at the indicated aspects and elevations:  avoid riding relatively shallow, unsupported slopes, avoid trigger points, and avoid big steep terrain.

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