Avalanche forecast

Northern Wallowas

Wallowa Avalanche Center
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Avalanche danger

Fri
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
2 · Moderate
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Out of date — this forecast expired 6 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

Dangerous avalanche conditions exist in the Southern Wallowas.  Several generations of windslab are present in leeward loaded terrain that will be sensitive to a trigger of a person and machine today.  These windslabs have a strong possibility of stepping down into deeper layers of the snowpack and causing large, destructive, and unsurvivable avalanches.  Avoid consequential terrain, stay out from underneath overhead avalanche runouts, and steer clear of terrain traps.  The monsters are still sleeping in the basement. 

Avalanche problems

  • Wind Slabs

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

    Observers in the Southern Wallowas called the winds "switchy" yesterday.  Our Kip Rand weather station is still reading incorrect wind directions, but the wind speeds are accurate- and they wind speeds for the last couple of days have been prime for transporting snow onto leeward terrain.  Look for evidence of fresh wind loading in smooth, hollow sounding pillows.  Utilize small and safe test slopes to check for reactivity of these freshly formed windslabs.   Avoid slopes that have recent wind loading, and check for bonding of the "older generation" of windslab that could be buried in the top foot of the snowpack.   A large natural avalanche was reported along the Norway peak ridgeline (east facing at about 8500') and was estimated to be 3 feet deep and 1000' wide.  While likely starting as a windslab, this avalanche seemingly stepped down into older weaker snow deeper in the snowpack.  

  • Deep Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2–3

    Deep Persistent Slab.  This is what keeps me up at night.  The low probability/high consequence nature of these avalanches combined with a large amount of spatial variability demand what I would call a patient avoidance tactic.  Don't try to out-wit, out-trick, or out-run this type of monster.   Since the morning of Monday 1/4, an additional 34"/85cm of snow has fallen at 7000' in the southern Wallowas.  Schneider Meadows Snotel at 5400' has registered an additional 2.4" of Snow Water Equivelant since that time.   The Solstice Rain Crust (SRC) can be seen in the picture as the grey stripe a little more than halfway down from the snow surface.  The foot of hard consolidated snow below that is capping the "Old November Facets" which have very little cohesion and are a very weak layer.  While getting harder to trigger, all that is needed is to find an area of shallower snow that will be more easily triggered by a machine or person and bam- you have a deep slab avalanche.  Make conservative terrain choices staying out from underneath avalanche paths, avoid terrain traps, and if travelling in the runout of an avalanche path- regroup further out of the runout than you think is necessary.  

    (1/6/2021) Southern Wallowas Snowpack continues to stack up, but the weak snow now buried 5 feet deep will continue to plague the stability.

Avalanche Discussion

There is a very complex nature to the snowpack at this time with a variety of slabs, crusts, and weak snow lying throughout the deepening snowpack.  The Deep Persistent avalanche problem type will be the most destructive, but the windslab problem in leeward terrain will be the most likely today.  As stated above, there is a good chance that the added weight of debris from a wind slab could easily trigger a deeper slab avalanche.  In Killian's ECT below, he has finished the loading steps of the test and did not get any propogation.  He continued to load the column and got full propogation of the Old November Facets buried 5 feet (150cm) deep.  The additional loading steps on this test could be likened to a rider digging a track deeper into the snowpack, thus putting added stress on these deeper weak layers.  I know what your thinking....Why isn't the Deep Persistent Slab problem at lower elevations?  Well that's a really good question.  What observers have been finding is that there is not the connectivity of the slab of snow at lower elevations.  The weak sugar snow that developed through the first couple weeks of December's high pressure is still there, but the slab isn't as strong or cohesive above these layers at that elevation.  Excellent riding has been reported on low angle terrain below treeline.  

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