Bollettino valanghe

Northern Wallowas

Wallowa Avalanche Center
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Pericolo valanghe

Sat
Alta quota
3 · Marcato
Limite del bosco
2 · Moderato
Sotto il limite
2 · Moderato
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In sintesi

Winds overnight or this morning could create dangerous wind-drifted snow at mid and upper elevations.  February's 1.5-3' of snow sits on a foundation of weak old snow grains on all aspects at mid and lower elevations.  Evaluate snow and terrain carefully, identifying features of concern, especially trauma boosters like trees or burial intensifiers like gullies.  

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Problemi valanghivi

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    1–2

    Moderate winds (17-25mph) can deposit snow 3-5x deeper than what fell from the sky.  4" of new snow could become a 12-20" thick windslab.  Boots sinking down to the knee or thigh yesterday highlights how much snow is available for transport.  Seeing blowing snow is a sign to rein it in.  

    In all terrain, look for textured, rippled or unusually smooth surfaces, or snow that suddenly supports your skis, board or machine.  Feel or listen for hollow or drum-like sounds,  Avoid these features in avalanche terrain.  But take photos!

    Dry loose avalanches may be small today, but they could knock you off your feet or into somewhere you don't want to be.  

    (2/5/2025) Photo: Caleb Merrill

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1.5–2.5

    The thickness of the overlying slab varies from 1.5-2.5' (or more with wind loading). The persistent weak layer below can be summarized:

    • On shady and wind-sheltered northerly aspects, February's snow has not bonded well to the 10-12" of weak, sugary facets and/or surface hoar.  
    • On solar aspects, a buried melt-freeze crust may provide a slick bed surface and harbors weak sugary snow below it.  We have had one confirmation from the S Wallowas of a persistent slab triggering below the 1/31 melt-freeze crust.  

    With each day of snow or wind loading, the weak layer is stressed more.  There is uncertainty about when it reaches its tipping point on a particular slope and is reactive to a human trigger.  

     

     

Avalanche Discussion

A persistent slab needs two ingredients: a weak or soft layer of persistent grains (the facets we've been finding for weeks) and a stronger or harder layer above (the new snow this week).   As the name suggests, the persisting layer will stick around and be slow to strengthen. 

What to do:   A persistent slab avalanche needs two more ingredients: a slope greater than 30 degrees to initiate, and a natural or human trigger.  With uncertainty about which slopes have the right combination of slab ingredients to be unstable enough, you can hedge your bets by choosing low-angle terrain or, at the least, inconsequential pieces of avalanche terrain. 

As always, be on the lookout for the freebie signs of unstable snow: recent natural avalanches, shooting cracks, and whumphing of the snowpack.   With a persistent slab problem, the absence of these clues does not mean that a slope is safe to ride, and careful evaluation should be used. 

Observations:   No obs received yesterday from the Wallowas.  Northern Wallowas and Southern Wallowas reports from Weds, Feb 5, highlight surface wind effect and concerning test results down 1.5' on a mid-storm layer (likely changed or healed since then) and 2.5' down on the 1/31 crust, including one column so weak that it failed on isolation.  A ski guide nearby also found similar propagating tests on the same two layers at NW 7100'.  

Elkhorns: I traveled in Angell Basin Thursday and found unreactive soft windslabs above 7900' and a persistent slab structure on northerlies Near Treeline, but not Above Treeline.  

 Here are Southern/Western Wallowas reports on 2/4 from a current and a former forecaster.   There have been no observed persistent slab avalanches in the Burger Butte/Taylor Green area, with two nearby suspect northerly mid elevation slopes producing wind slabs instead.  

Add value to your avalanche forecast.  Help us reduce uncertainty.   If you get out today, please submit an observation sharing where you traveled and if you saw avalanches or signs of instability.  How deep your boots sink into the snow is an easy gauge for how much snow the wind might transport.  

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