Bulletin d’avalanche

Elkhorns

Wallowa Avalanche Center
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Danger d’avalanche

Sat
Alpin
3 · Marqué
Limite forestière
3 · Marqué
Sous la limite
2 · Modéré
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Périmé — ce bulletin a expiré 3 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

It remains likely that a rider could trigger a large deadly avalanche failing on buried weak snow 2-4 feet deep.  Increasing winds throughout the day will build sensitive wind slabs in exposed terrain.  If you are keen to not be in an avalanche, stick to low-angle slopes, avoid avalanche runout zones, and avoid wind-loaded terrain.

This forecast is sponsored by Anthony Lakes Mountain Resort.

Problèmes avalancheux

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    1–2

    The snowpack structure in the Elkhorns remains poor.  The last week has brought about 1.5" of Snow Water Equivelent.  This has not been enough weight to tip the balance on the weak snowpack structure with natural avalanche activity, but the snowpack is primed and waiting for a trigger.   WAC Pro observer Karen Morse has a great observation from yesterday that can be found here.  She found a couple thin crusts within the upper foot of the snowpack.   Two main layers of concern were identified.  One was a foot from the surface, and the other was anywhere from 3-4 feet from the surface.  Another great ob from last week in the Hoffer Butte area can be found here. 

    As time progresses, this problem will have a lower likelihood, but the consequences will remain real.  We are starting to see less consistency in our snowpack tests, with some tests not showing propagation.   Remember that the poor snowpack structure always trumps a "false negative" snowpack test.  Snowpack tests are not decision-making tools, and offer a single data point in a sea of spatial variability.  It's becoming less evident if you just look at the snow surface, as obvious signs of instability may not be present.  The cracking and whumphing (collapsing) that we observed last week has decreased, and the slab may be able to hold the weight of a rider until the slab thickness decreases somewhere in the terrain.

    Remember what we need for a slab avalanche? Slab + Weak Layer + Bed Surface.   We've got it! When we put that in terrain steep enough to slide and introduce a trigger, we get a slab avalanche.   

    If you want to avoid avalanches, you should stay off of slopes greater than 30 degrees, stay well clear of avalanche runout zones, and not ride above terrain traps.  Don't trust these facets until they are swimming in the river!  

     

    (1/25/2024) Photo: Karen Morse

    SE 7700'

  • Wind Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    1–2

    There is still some snow on the surface to be transported by the wind.  As winds increase ahead of the warm front today, expect to see sensitive wind slabs up to a foot deep in exposed terrain.  You will likely find these at mid and upper elevations along exposed ridgelines and cross-loaded mid-slope terrain features.  Be observant for a rippled and stiff snow surface, and cracking from your boards or machine.  Cornice development may be evident on the leeward sides of ridgelines.  A cornice or wind slab failure could be enough weight on the right slope to trigger a deeper more destructive persistent slab avalanche.  

    (1/11/2024) Photo: Caleb Merrill

Avalanche Discussion

As the 4-5 foot slab continues to strengthen and become even more cohesive, the weak sugar snow will continue to be a real threat.  It's becoming less evident if you just look at the snow surface, as obvious signs of instability may not be present.  The cracking and whumphing (collapsing) that we observed last week has decreased, and the slab may be able to hold the weight of a rider until the slab thickness decreases somewhere in the terrain.   

Seeing tracks on a slope does not mean it is safe to ride.  Persistent slabs are notorious for allowing unsuspecting riders to lay numerous tracks without incident before one unlucky rider finds a thin spot in the snowpack, collapsing the weak layer and creating a large, destructive avalanche.  Common thin spots in the snow often develop around rocky steep rollovers, or where the wind has stripped snow from the up-wind (windward) sides of ridgelines. 

Towards the end of today and into the weekend as our temperatures warm and our freezing levels rise, wet loose avalanches in terrain steeper than 35 degrees will likely occur.  You may notice a cohesionless snow surface from warming or rain.  If you step off your machine or out of your skis, and are sinking to the top of your boot, it's time to scoot! 

Now is not the time to push the terrain.  Patience is the name of the game with persistent slabs.  Read the forecast in its entirety, make a conservative travel plan that allows for wide terrain margins, use clear communication with your partners, listen to your gut, and speak up.  

We appreciate all of the observations that have been coming into the WAC from all of our zones.  It truly adds value to your forecast.  Keep 'em coming! Submit your obs here. 

Kelly McNeil will bring you the forecast through the weekend.  Expect some changes with warming temps and rising snow levels.  

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