Bollettino valanghe

Mt Hood

Northwest Avalanche Center
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Pericolo valanghe

Thu
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
2 · Moderato
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Non aggiornato — questo bollettino è scaduto 6 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

Wet slabs linger long after heavy rainfall, producing widely propagating avalanches on slopes as shallow as 30 degrees while wet loose avalanches may be triggered early in the day in wet surface snow on slopes steeper than 35 degrees. Very large dry snow avalanches from the upper mountain on Mt. Hood may also run many thousands of feet, entraining snow down to valley bottom. Maintain an extra margin of safety for these low probability high consequence avalanches occurring primarily in large avalanche paths and threatening to valley bottoms.

Problemi valanghivi

  • Wet Slabs

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

     4" of liquid water (48-hour expected total) should be percolating through the Mt. Hood snowpack by the time surface temperatures cool early Wednesday morning. Snow levels will remain above the NWAC forecast area overnight before dropping rapidly early Wednesday. While the surface may gradually refreeze from the top down, plenty of water will continue to lubricate crusts in the snowpack. Prior to this storm cycle, the upper snowpack consists of mostly dry snow with a number of crusts interspersed within it. If water pools on any given layer, the saturated slab of snow above will create a large or even very large wet slab that could fail on slopes as shallow as 30 degrees. Wet slabs are very tricky to predict, so we may see no wet slabs or it could be more active than we expect. Evidence of recent large or very large avalanches is the first clue that things may be more dangerous. In the absence of direct evidence, you can also dig down a meter in the snowpack to see if there is free water in the snow. The best strategy when you have a low probability high consequence problem is often to steer around large avalanche paths, choosing smaller terrain features, ridges or forested terrain to maintain your margin of safety.

    Shallow fresh snowfall may insulate the snow surface and help slow the refreeze. If you find wet or sticky snow that you can sink into up to your boot top, then steer around slopes steeper than 35 degrees to avoid a Wet Loose avalanche problem.

    (1/12/2021) A very large natural wet avalanche in the Wellington slide path near Stevens Pass.

  • Wind Slabs

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

    Decreasing moderate to strong winds will blow shallow fresh snow into slabs that may be reactive on specific terrain features where they form pockets of dry snow more than 6" deep. Cracking of the snow surface, recently formed cornices, and lens-shaped pillows are all indications that wind slabs lurk. Steer around wind-loaded slopes steeper than 35 degrees. Be mindful that with potentially overlapping avalanche problems, a small wind slab could trigger a more dangerous wet avalanche, such as a larger loose wet or potentially even a wet slab.

    Example: Textured snow surfaces and blowing snow are great clues that wind slabs may exist on the slope below.

Avalanche Discussion

Above 8500 ft on Mt. Hood, the 4" of water received since Monday translated into massive amounts of snow. Very large dry snow avalanches may initiate at these elevations, particularly early in the day as winds continue to overload lee slopes. Some of these avalanches have the potential to run and entrain saturated snow, gaining mass for thousands of feet and entraining to valley bottoms.

We're just exiting a major avalanche cycle throughout the region, but we have no observations in the past 36 hours to document the extent of the cycle. This adds a degree of uncertainty to our forecast which is compounded by already difficult-to-predict wet snow avalanche problems. What can you do about the uncertainty? Adjust your mindset to travel more conservatively in order to manage the low probability of a high consequence incident. Assess conditions as you travel and stick to known safer terrain without significant exposure from above.

During the ongoing Covid-19 pandemic, continue to follow the latest guidance from local, state, and federal health officials. Avoid unnecessary risks that could impact first responders and stress medical resources.  Wear a mask when appropriate, practice social distancing, and consider recreating closer to home.

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