Bulletin d’avalanche

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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 last year. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

It remains possible to trigger avalanches in steep wind-loaded terrain.  Shooting cracks, collapsing of the snowpack, and recent avalanches are all bulls-eye clues that the snowpack is unstable.  Avoid wind-stiffened drifts of snow in terrain steeper than 30 degrees to decrease your chances of getting caught in an avalanche.  

Problèmes avalancheux

  • Wind Slabs

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

    The storm that arrived Tuesday and continued through yesterday morning was accompanied by strong winds.   In mid and upper-elevation exposed areas, the wind redistributed the snow into dense slabs of cohesive snow.   These wind slabs could remain sensitive to the weight of a rider today and could be large enough to bury, injure, or kill a person.   They are most likely to be found on West through North through East aspects at mid and upper elevations.  These avalanches will run fast and far where the underlying bed surface is a firm crust.  Look for clues to wind loading such as a rippled or stiff snow surface, cracking around your skis or under your machine, and fresh cornice development along ridgelines.  Use small test slopes with little consequence to test the reactivity of wind slabs.  

    Yesterday in the Northern Wallowas, observers found the windward (south and east aspects) sides of ridgelines blown down to the old snow surface, while the leeward (north and west aspects) were loaded with dense drifts.  A couple of natural small wind slab avalanches were noted just under a corniced ridgeline on a North aspect around 8,000'.  Cat ski guides from Anthony Lakes reported shooting cracks from the snow cat driving through wind drifts.  Ski guides in the Norway Basin zone skied windward (Southwest) aspects near treeline and found little reactivity at the interface of the new/old snow.  They had some views into the alpine and saw no natural avalanches.  

    Today, the forecasted wind speeds are generally 15-20 mph out of the South and Southwest and we could see some higher gusts.  This will continue to load leeward aspects along ridgelines and mid-slope terrain features.  

    (3/7/2025)

    Wind Slab Formation along Lees shoulder

    Photo: Caleb Merrill

Avalanche Discussion

Reports yesterday from the Northern Wallowas indicated 10-12" of new snow at Wing Ridge with wind-drifted snow depths up to 16-20" deep.  Field reports from Anthony Lakes included an average settled storm total of 8-12" with less in wind-scoured locations.   In the Norway Basin area, reports are that there was no new snow accumulation below 6800', but 6-12" of settled storm snow from 7300' and higher.   Check out an observation from yesterday at Wing Ridge here.

There are mixed signals of how well the new snow has bonded to the old snow surface.  Under the new snow, a firm melt-freeze or wind crust exists on most all aspects and elevations (except for the rare upper elevation, wind-protected, northerly aspects).  In the Northern Wallowas, snowpack tests indicated easy propagation of a layer of weaker snow near this melt-freeze crust.  In the Southern Wallowas, on windward aspects, observers found good bonding to the old melt-freeze crusts with plenty of graupel in the new snow.   

In wind-sheltered terrain, get curious about how well the new snow has bonded to the old snow surface.  The best way to assess this is through hand pits:  isolate a block of snow using your hand or ski pole and pull on the back of it to see how well it is bonded to the old snow surface.   If you can pick up the slab of snow and it cleanly shears off the old snow surface, you should remain weary of storm slab avalanches and avoid steep terrain.  On steep slopes where new snow lacks the quality of a cohesive slab, be aware of loose dry avalanches running fast and far on old, firm crusts.   These might not be big enough to bury you, unless they push you over or into consequential terrain traps such as cliffs, gullies, or dense trees.  

Expect the avalanche hazard to rise back up after today, with larger snow totals on the horizon starting this evening.  

It is time to take a step back in your terrain selection.   To hedge your bets and decrease your odds of getting caught in an avalanche, stick to simple terrain under 30 degrees and avoid recently wind-loaded terrain features.  If traveling in avalanche terrain, remember good travel and communication protocols:  Expose only one person at a time, keep eyes on your partners, and regroup well clear of avalanche path runouts.   Keep clear lines of communication open with your partners, respect the veto power of someone who wants to dial it back, and be clear with your intentions.  

Engage with your backcountry community and forecasters.   Submit an observation here and help us reduce uncertainty.  It can be simple, short, and even anonymous.  Thank you! 

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