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Wallowa Avalanche Center
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2 · Moderado
Límite del bosque
2 · Moderado
Bajo el límite
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Desactualizado: este boletín caducó 4 years ago. Estás viendo condiciones pasadas, no el boletín vigente.

Lo esencial

Moderate to strong south winds have created a fresh round of windslabs up to a foot deep on Northwest, North, Northeast, and East facing slopes near and above treeline.  Avoid windslabs by looking for clues to recent windloading such as hollow sounding snow, rounded pillows, and cracking from your boards or machine.   It remains possible to trigger a deeper, more destructive avalanche on persistent weak layers within the snowpack, especially in areas that harbor shallower snowpack depths.  Careful evaluation of the snowpack structure remains critical if commiting to terrain greater than 30 degrees today.   

 

Today's forecast is sponsored by The Trailhead Bike and Ski Shop in Baker City.  

Problemas de aludes

  • Wind Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Possible
    Tamaño
    1–2

    Moderate to strong south winds have created a fresh round of wind slabs up to a foot deep on leeward slopes near and above treeline.  These windslabs will be recognizable by looking for rounded smooth pillows of snow that will sound hollow, feel stiff, and may crack around your boards or machine.  Look for these clues and avoid freshly wind loaded slopes and cross loaded mid slope terrain features.  Avoid riding above terrain traps such as cliffs, gullies, creeks, or slopes that abruptly transition to flat terrain as even a small wind slab avalanche could confine debris into deeper amounts.  

    Stiff snow developing into a windslab on a north aspect at ridgeline in the northern Elkhorns yesterday.  

  • Deep Persistent Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Possible
    Tamaño
    1–3

    It remains possible for human triggered avalanches to fail on deeper buried persistent weak layers within the snow pack.  The snowpack contains several concerning persistent weak layers that vary in depth from 1.5 to 8 feet.  This is becoming a low likelihood, high consequence type of event that is hard to predict, often times producing inconsistent results in stability tests and offering little feedback in the form of visual clues from the snowpack surface.  Utilizing slope scale evaluation before committing to terrain features greater than 30 degrees in slope angle will be critical to avoid a deep slab avalanche.  There is a high amount of uncertainty when dealing with this type of avalanche problem, and it is recommended to hedge your bets with wide terrain margins.  Excellent riding conditions exist on the north side of the compass in terrain that is less than 30 degrees.   It is recommended to focus on the poor snowpack structure, not potentially inconsistent stability test results before committing to riding any slope steeper than 30 degrees.  See the forecast discussion below for more information. 

Avalanche Discussion

We are dealing with a complex snowpack right now throughout our forecast region.  The Christmas rain crust exists in all areas, but varies in depth and thickness.  It is found within the top 1-2 feet of the snowpack.   Forecasters and observers have found it to be around 3" thick at lower elevations and around 1" thick to almost none existent at the above treeline elevations.  We have found weaker snow above and within the crust at many locations that have produced sudden collapse fractures in compression tests and propagation in extended column tests.   As the snow above this crust stiffens with time and wind loaded snow, the chances of triggering an avalanche on this layer of concern increases.  

In the Western and Southern Wallowas, observers and forecasters have been tracking a layer of buried surface hoar that was buried on December 8th.  This adds complexity to the snowpack, and we think this layer was responsible for a snowmachine triggered avalanche in the Fish Lake area within the last week (see observation here).  We have found the December 8th Buried Surface Hoar below treeline and near treeline in areas protected from sun and wind on Southwest, West, North, East and Southeast aspects.  Stability tests have been producing alarming results including Sudden Planar compresion test results and propagation in Extended Column Tests and Propagation Saw Tests.  It remains possible for human triggered avalanches to fail on this layer, then step down into deeper weak layers near the ground- producing very large avalanches on large open slopes. 

Weak sugary facets at the base of the snowpack continue to show reactivity in stability tests with sudden collapse compression test results in shallower snowpack areas, and alarming Propagation Saw Tests in deeper snowpack areas.  In many areas, this deep weak layer is below a stiff (1F-P hard) slab.  The chances of triggering an avalanche on this layer is greater in areas that have a shallower snowpack depth, such as rocky or wind scoured areas.  

See the videos below from some of our forecaster observations within the last week from the Western Wallowas and Elkhorns. 

The deep persistent avalanche problem we are dealing with takes time to heal.  While we may not be seeing natural or human triggered avalanches failing on the weak snow near the ground, the poor structure still exists.  It takes discipline and patience on the human side of the avalanche equation while we are dealing with this problem.  Stay out from underneath overhead or adjacent avalanche paths while regrouping or taking breaks.  If you do decide to commit to terrain steeper than 30 degrees after carefully evaluating the snowpack, it is essential to have only one person on the slope at a time, while keeping a good eye on your riding partners.  

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