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
3 · Marcato
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Non aggiornato — questo bollettino è scaduto 2 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

Triggering avalanches in recent storm snow and wind drifted snow will be likely on Saturday. This is not the day to push into consequential terrain. Triggering avalanches above cliffs, rocks, trees, and gully features can lead to a worse outcome. You can minimize your exposure to avalanches by sticking to slopes less than 30 degrees steep. 

Problemi valanghivi

  • Storm Slabs

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

    Storm slab avalanches can happen anywhere the wind has not stripped the snow away. As snow continues to pile up, storm slab avalanches will have the chance to become large. On Friday, COAC observers found multiple mid-storm instabilities within the new snow from the last 48 hours. Steep, convex, and unsupported terrain are the classic features for triggering storm slabs. 

    On Friday, skier triggered storm slab avalanches were observed on northwest facing slopes near treeline. The avalanches were small (D1) and were easily triggered. 

     

    Archive Photo (Gabriel Coler)

    Example of a small storm slab avalanche in fresh snow.

  • Wind Slabs

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

    We have the right combination for wind slab avalanches - new snow and forecasted wind speeds in the upper teens to mid 20's mph. I expect slabs to build overnight and on Saturday. Wind slabs are most sensitive to triggering when they are fresh. 

    Wind slabs can be tricky becasue some lee terrain features may lack wind deposited snow while others will have monster drifts. If you have uncertainty about the wind loading on a slope 30 degrees or steepr, the safe bet is back off. We can expect to find wind slabs below ridges and high points, and other features that collect blowing snow. Crossloaded slopes caused by wind blowing aross the terrain will also be something to watch for on Saturday. Any time you see cracking in recent wind deposited snow or recent avalanches, recognize these as signs of unstable snow. 

    Some food for thought - you can find lee terrain features on the windward side of a mountain.

    Keep an eye on blowing snow and wind slab development in areas of dead forests and clearings in areas you typically think of as below treeline. 

    Archive Photo (Aaron Hartz)

    Cracking in wind slabs are a good indicator that you can trigger an avalanche.

Avalanche Discussion

Cornices will build at ridgetops. New cornices are fragile and easy to break through and can result in a fall down the slope below.  Be catious when approaching ridges; try to get a good vantage point to determine if a cornice is present.

COAC observers have not located any buried surface hoar despite seeing it on the surface before the snow started falling. I want to keep it in mind as we continue to look for it. Buried surface hoar can create a sensitive weak layer in the snowpack and can lead to avalanches breaking wider and running farther than usual. 

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