Bollettino valanghe

West Slopes South

Northwest Avalanche Center
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Pericolo valanghe

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

A potent winter storm on Saturday night will result in dangerous avalanche conditions throughout the West South zone on Sunday. As you ascend in elevation, avoid slopes over 35 degrees where slides large enough to bury and kill you are expected. In isolated locations, you may see avalanches fail naturally or break in surprising ways, wrapping terrain features or spanning far distances.

Problemi valanghivi

  • Storm Slabs

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

    Saturday night's storm should deliver a good shot of snow across the zone, accompanied by wind and rising freezing levels. These are all common ingredients to create a storm slab problem.  Slabs should be larger and more sensitive as you ascend in elevation, in wind-loaded terrain, or on the volcanoes where more snow is forecast. Use small test slopes or quick hand pits as you travel to determine how the new snow bonded to the old surface or if it is "upside-down" (heavy snow over weaker snow). Cracking of the surface or new avalanches are red flag signs of instability that you shouldn't ignore. Avoid open slopes over 35 degrees until the snowpack has had time to adjust to the new load. 

    If this storm was occurring during the daylight hours, we would be talking about the potential for large natural avalanches, especially on the volcanoes. You may still see naturals occur, particularly in the morning hours.

    (1/3/2025)

    A human-triggered avalanche near White Pass. This slide broke widely and was triggered from further back on the ridge. [N 5500']

  • Loose Wet

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–1.5

    As mentioned above, the storm is ending on a warming trend. Once temperatures bump up, expect rain to fall on the new snow at lower elevations, How much rain is tough to say, but the initial onset should be during the overnight hours. That means that peak instability for wet avalanches should be over by the time you step out of your car on Sunday morning. At that time, it won't be hard for you to tell if you need to consider these slides as you travel. If the snowpack is wet or it's still raining, be leery of slopes over 35 degrees or rocky ledges where wet avalanches are more likely. Don't let a small slide push you into a creek or hole where the consequences are higher. 

    Another hazard to consider with this warm-up are the tree bombs. They're huge right now! As temps rise, the wind blows, and rain potentially falls, these large chunks of ice and snow could fall. They're a hazard in their own right, but can also trigger avalanches on slopes below, similar to a cornice collapse. 

    (12/20/2024)

    Wet avalanche debris on a steep slope after a rain on snow event a few weeks ago.

    Photo: Dallas Glass

Avalanche Discussion

Our two-week storm cycle is coming to an end. Sure, we've had a few days off, but it's been consistently snowing and blowing since the formation of the Solstice Crust, roughly doubling our snowpack depth in the process. Saturday night will be the grand finale before we head into a drier weather window for the upcoming work week. Storm totals should vary greatly across the zone, with Paradise receiving the high end. Regardless of your location, avalanche hazard may be highest first thing in the morning as the storm wraps up.

While most avalanche activity is expected to involve the new snow, recent observations indicate there may be deeper instabilities. On Friday, there was a remotely triggered slab near White Pass, and NWAC forecasters got propagating test results near Crystal. In the neighboring East South zone, they are forecasting a persistent slab problem for a layer that has some similarities to these observations. It's not quite apples to apples, but this is a recent development and warrants more investigation. Be sure to check not just the bond to the old surface, but layers roughly another foot down for issues. If you see avalanches breaking widely or wrapping terrain features, step your terrain choices way back. 

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