Bulletin d’avalanche

Elkhorns

Wallowa Avalanche Center
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Danger d’avalanche

Sat
Alpin
2 · Modéré
Limite forestière
2 · Modéré
Sous la limite
1 · Faible
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Périmé — ce bulletin a expiré 2 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

It remains possible to trigger a large destructive avalanche that could fail on weak layers in the upper 3-4 feet of the snowpack.  Avoid being on or under steep slopes in the afternoon if you are encountering wet sloppy snow.  

This forecast is sponsored by Brooks Painting 

Problèmes avalancheux

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    1–2.5

    As your search for soft snow leads you to shadier aspects, you need to have your wits about you. 

    Several persistent weak layers exist in our upper snowpack.  Forecasters and observers have been tracking two layers of Buried Surface Hoar that have shown a concerning level of reactivity in snowpack tests.   These persistent weak layers have been found between 1-2.5' from the surface and are mostly on Northwest-North-Northeast aspects near and above the treeline.  A slab of cohesive snow sits above these layers, and as this slab has stiffened, we have not been seeing obvious signs of stability without digging into the snowpack to look for the layer and test its reactivity with snowpack tests.  This means that the freebie red flag signs of instability such as cracking or collapsing (whumphing) will likely not be present as you travel in areas where these weak layers exist.   The zones where these layers have been noted the most are the Western and Southern Wallowas as well as the Elkhorn Mountains.   In my travels yesterday in the Northern Elkhorns, I found the 2/26 Buried Surface Hoar in one out of 4 snowpits that I dug.  Most likely places to find it are on shady aspects near treeline that are protected from the wind.  Check out my observation here.  

    The Rain Crust that was buried on February 1st has weak snow around it and should also be on your radar.  This layer has been found about 3 feet from the surface of the snow and sits below a hefty cohesive slab.  

    In shallower snowpack areas on Northerly aspects that hold snowpack depths of around 3-4 feet, there remains an off chance to trigger a deep persistent slab avalanche that could fail on weak faceted snow near the ground.  An avalanche of this magnitude would be catastrophic.  

    To decrease your chances of getting mixed up in this sort of fight, a thorough snowpack analysis is suggested before committing to any slope greater than 30 degrees on Northeast through Northwest aspects near and above treeline.  When you have uncertainty around the presence of these persistent weak layers, choose simple terrain less than 30 degrees.  

  • Loose Wet

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    1–1.5

    The last week of warm and sunny weather has melted snow in the upper snowpack and water has dripped through the snow until it has reached a crust buried in the upper 2 feet of the snowpack.  This has created unstable upper snowpack conditions during the heat of the day.   Many natural wet loose avalanches have been observed since last weekend.  These often occur on solar aspects near rocks or cliff bands.  Last night, temperatures dropped below freezing at most upper elevation weather stations.   While we are on the back end of the action in concern to the wet avalanche problem, be mindful that the likelihood of triggering wet loose avalanches in terrain steeper than 35 degrees during the afternoon hours remains possible-especially if the sun is heating up solar aspects.    

    Cloudy skies can help slow the onset of natural wet loose avalanches as the amount of direct sun that warms the surface of the snow is reduced.  That being said, the upper snowpack has been affected by strong solar input and multiple days without freezing temperatures and will take some time to lock back up once temperatures start to drop.   Even a smaller wet loose avalanche has the potential to knock you off your feet and carry you over consequential terrain or push enough snow into a terrain trap to bury you.  

    In your travels in the mountains today, pay attention to how wet the snow is under your feet or machine.  Get curious and dig down a few feet and see how wet the surface snow is as well as how deep water has percolated in the snowpack.  If you step off your machine or boards and are sinking up to your boot tops in wet snow, it's time to head to terrain less than 30 degrees in steepness.  

    Wet Loose avalanches on an East aspect at 8,000' in the Western Wallowas.

    Photo: Wallowa Avalanche Center

Avalanche Discussion

Stay vigilant in your mountain travels and snowpack assessment.  Many of us have built a mental winter road map that suggests stabilizing deeper snowpack conditions by this point in the winter.  The weather and snowpack this season demand that we recalibrate that operational memory and accept the current conditions.  Make a conservative travel plan to avoid areas where you have a higher level of uncertainty around the presence of persistent weak layers. 

As daytime temperatures increase this afternoon, avoid being on or underneath steep terrain that is holding wet uncohesive snow.  

The recent warm spell has destabilized cornices to the point that they could break naturally or as you step or ride near them.  Check out Wallowa Alpine Huts guide Killian Sump's observation from last week here that notes several natural cornice failures and a recent slab avalanche.  Give cornices a "wider than you think" buffer.  

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