Bollettino valanghe

Blues

Wallowa Avalanche Center
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Pericolo valanghe

Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
1 · Debole
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Non aggiornato — questo bollettino è scaduto 3 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

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 by Brooks Painting

Problemi valanghivi

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–1.5

    The 6-8" of new snow we've received in the last 48 hours has been easily transported by SW winds and deposited on NW-E facing terrain at and below ridgeline.  Expect to find reactive wind slabs a foot thick or more with human-triggered avalanches being a real possibility.  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 features mid-slope like on the leeside of ribs and sub-ridges. Look for smooth pillows with a dabbled texture and if you get any kind of shooting crack or hollow-sounding snowpack underneath you, then you should scramble for the exit by staying off and out from underneath avalanche terrain. 

    Winds have been light overnight, however they are forecast to pick up in the afternoon and veer from SW - N - NE - S throughout the day. This may lead to some interesting loading patterns near ridgeline. Pay close attention to surface features that indicate wind deposition and expect potential wind slabs in unexpected places. 

    (1/11/2024)

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

    Photo: Caleb Merrill

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Unlikely
    Dimensione
    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 sledder or 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.  Recreationsist should continue to be vigilant and seek out critical snowpack information to assess the reactivity of these deeply buried weak layers. The consequences of triggering an avalanche on these weak layers would be severe. 

The new snow has fallen 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). 

A big issue out there is that we had widespread surface hoar formation during the recent dry spell and cold clear nights. 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. Not a good situation.  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 propogate 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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