Avalanche forecast

Olympics

Northwest Avalanche Center
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Avalanche danger

Sat
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
2 · Moderate
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Highlights

A warming storm with limited moisture will bring snow, fresh slabs, and a changeover to a wintry mix or rain. Steer around shallow wind drifts near ridgelines or convex rollovers in the morning. Once temperatures rise above freezing, avoid all slopes steeper than 35 degrees as wet loose avalanches may entrain dry snow.

Avalanche problems

  • Loose Wet

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–2

    Rapid warming events introduce huge uncertainty into any avalanche forecast. A transition from snow to rain on a cold snowpack can destabilize slopes over a very short period of time. The uncertainty associated with the weather forecast warrants a more conservative trip plan that maintains lower-angle exit routes for when the rain falls on our dry, cold snowpack. Liquid water impacting snow has us most concerned and should be most likely near or above treeline as low-level cold air remains entrenched in the valleys. There's plenty of light, dry snow around to entrain, so even if rainfall remains light, expect loose avalanches to run naturally and entrain up to 1-2 ft of previously dry snow. If it starts to rain, travel safely along ridgelines and more thickly treed slopes avoiding open slopes steeper than 35 degrees.

    Example: Potentially large wet loose avalanches as warming/rain destabilizes snow surfaces.

    Photo: Matt Primomo

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely
    Size
    1.5–2.5

    In some areas, you can still find a layer of surface hoar (12/18) buried 20-30 inches below the surface. We believe that it remains reactive on NW-N-NE aspects near and below treeline on wind-sheltered slopes. Steep, convex rollovers are where you are most likely to a large avalanche on this layer. While it was not found by rangers and avalanche professionals on 12/22,  you can read a couple observations from last weekend HERE and HERE.

    Buried surface hoar maintains notoriety for producing avalanches that can release on a low-angle slope, break above you, propagate widely, or trigger remotely. Whumphs and rumbling collapses provide a warning that the risk of triggering an avalanche may be locally elevated.

    (12/17/2022)

    An obvious layer of buried surface hoar, seen as a thin grey line in this pit wall, is the culprit right now. 

    Photo: Matt Lubar- Cascade Mountain Ascents

Avalanche Discussion

Westerly winds stripped dry snow off W and NW aspects, depositing them on E aspects this since the last major storm, producing large wind drifts which are gradually losing reactivity. Soft, dry snow remains abundant on many aspects and this snow will be available to form smaller fresh slabs while temperatures stay below freezing on Friday. Note active wind transport and steer around lens-shaped pillows most likely in typical avalanche start zones.

Avalanche conditions may be easier to manage in the morning than the afternoon. Continue to adjust to changing weather conditions and if you see anything out of the ordinary, further reduce your terrain selection.

If you make it out on Friday, share what you saw with us by submitting an observation. The more information we have, the easier it is to produce an accurate forecast so that you can have a safer day in the backcountry. 

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