Boletín de aludes

Blues

Wallowa Avalanche Center
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Peligro de aludes

Alta montaña
2 · Moderado
Límite del bosque
2 · Moderado
Bajo el límite
1 · Débil
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Desactualizado: este boletín caducó 3 years ago. Estás viendo condiciones pasadas, no el boletín vigente.

Lo esencial

There remains the possibility of triggering wind slabs a foot thick or more at upper elevations on the leeward side of ridgelines and cross-loaded terrain features mid-slope.  It also remains possible to trigger a deeper and more destructive avalanche in persistent weak layers buried 2-6' deep in the snowpack.  To avoid avalanches, steer clear of terrain steeper than 30 degrees, wind-loaded slopes, and areas that harbor a shallow snowpack (less than 3 feet).  

This forecast is sponsored Anthony Lakes Mountain Resort.

Problemas de aludes

  • Wind Slabs

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

    The 6-8" of snow that fell on Thursday and Friday has been easily transported by SW winds and deposited on NW-E facing terrain at and below ridgelines. Moderate S  winds today will continue to move snow building larger wind slabs. Expect to find reactive wind slabs a foot or more thick. Riders should avoid slopes > 30 degrees where recent signs of wind-loading are evident. This includes areas below cornices and ridgelines on NW - N - E facing aspects and cross-loaded terrain mid-slope features.  Look for smooth pillows with a dabbled texture and if you get any shooting cracks or hollow-sounding snowpack underneath you, then you should stay off and out from underneath avalanche terrain.

    (1/11/2024)

    Rippled Snow Surface and Cracking are good indications of wind slab development. 

    Photo: Caleb Merrill

  • Persistent Slabs

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

    The mild temperatures over the last week have helped to consolidate and strengthen the overall snowpack in the Blues. However, we are still finding poor structure in the lower snowpack that warrants the continuing assessment of a low-probability, high-consequence persistent slab problem. The weak layers in the lower snowpack are guarded by a dense and strong mid-pack layer that is well over a foot thick. Where this strong and thick mid-pack layer exists it will be difficult for riders to impact the basal (lower) snowpack weaknesses. Yeah! You all shout. But wait...there is a problem...the problem is spatial variability. There are places in the terrain where this mid-pack layer may be thinner and the weight of a rider could impact the basal weaknesses. The resulting avalanche could be a zinger. How do you manage this pesky problem? By avoiding potential trigger points in the terrain. Oh...what are those? Potential trigger points in the terrain include steep convex rollovers, rocky slopes, and outcroppings, areas with lots of alder and exposed bushes, and on the windward side of mid-slope sub-ridges. Another strategy to employ - only allow one rider to cross or be on a suspect slope at a time. This limits exposure and stress on the snowpack. 

    (2/15/2024) Photo: Wallowa Avalanche Center

Avalanche Discussion

The persistent slab problem continues to plague the Blue Mountains. There are weak layers toward the bottom of the snowpack that still remain a concern.  Recreationalists should continue to be vigilant and seek out critical snowpack information to assess the reactivity of these deeply buried weak layers. If you lack the skills to gather this snowpack information you should avoid avalanche terrain.  

Snow on Thursday and Friday fell on a variable and weak old snow surface. This has likely created instabilities at the old/new interface. Where storm totals are around 6" or less, or the new snow remains uncohesive, the main problem will be loose dry avalanches on slopes > 35 degrees. These small avalanches may not bury you, but they could inflict significant bodily harm if they were to take you off your feet or sled and sweep you into obstacles like rocks and trees. Where storm totals exceed 12" there will be a storm slab problem. The best practice for avoiding this problem is to stick to slopes < 30 degrees (i.e. stay out of avalanche terrain). 

There was widespread surface hoar formation before the Thursday- Friday storm arrived. Surface hoar is a notorious weak layer when buried. It can propagate fractures for long distances and while you may be on low-angle terrain, those fractures can propagate up onto a steep slope above you and release an avalanche. Likely locations for encountering buried surface hoar include more sheltered and protected slopes at and below treeline. If you are hearing the snowpack whoomph underneath you or seeing shooting cracks propagate outwards as you travel, then surface hoar is likely present at the old/new interface. This should have you dialing back your terrain choices and keeping off and out from under slopes > 30 degrees. 

 

 

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