Bollettino valanghe

Galena Summit & Eastern Mtns

Sawtooth Avalanche Center
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Pericolo valanghe

Tue
Alta quota
1 · Debole
Limite del bosco
1 · Debole
Sotto il limite
1 · Debole
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Non aggiornato — questo bollettino è scaduto 6 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

Large avalanches are unlikely today. Increasing wind speeds overnight are moving snow and building small slabs in exposed, upper elevation terrain. New snow falling this afternoon and tonight will provide the wind with additional ammunition. Look for these small slabs near terrain features that slow the wind down and force it to drop the load it is carrying, such as ridgelines, gullies, and ribs.

If you are traveling in the Pioneer Mountains, refer to the forecast for the Soldier & Wood River Valley Mtns.

Problemi valanghivi

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Unlikely
    Dimensione
    1

    In shaded terrain, the snow that fell last week has settled and gradually faceted, making for some great skiing and riding conditions ("recycled powder"). Last night, the wind picked up speed and began searching for what unconsolidated snow it could find. In areas with soft snow, this wind is moving snow and building small, isolated drifts. These will continue to grow in size as snowfall starts this afternoon. Look for these slabs near terrain features that slow the wind down and force it to drop the load it is carrying. Typical locations are along ridgelines, and near mid-slope terrain features such as gullies, and rocky ribs. Any slabs the wind builds today will be small and isolated. However, if you're traveling in very steep terrain the consequences of getting knocked off your feet and taken for a ride can be high. 

    ADDITIONAL DISCUSSIONSeveral observations have pointed to the existence of layers of weak snow buried in the upper snowpack. These layers have produced natural avalanches, cracking, collapsing, and unstable snowpack test scores. Without a significant recent load, these layers appear to be in a period of dormancy. However, where wind drifts are stressing these layers triggering an avalanche remains a possibility. Be alert to this possibility today and in the coming days as new snow further builds the slab on top of these layers.

    If you are traveling in the Pioneer Mountains, refer to the forecast for the Soldier & Wood River Valley Mtns to read about the persistent slab problem you may encounter.

Avalanche Discussion

The Avalanche Forecast is a tool that helps you to orient yourself to the types of problems you may encounter in the backcountry. It provides a starting point for your mental model of the hazards you will be dealing with on any given day. Let's walk through my day yesterday to get a sense for how you might use it:

The area I was heading (East Fork of the Big Wood) sits near the boundary between two zones, so I checked the forecast for both. Persistent slabs and wet loose avalanches were on the problem list and the forecast text specifically called out where I was headed as being problematic. I made a mental note of these issues, checked the weather, and headed out the door.

As I drove to the trailhead, the sound of refrozen mud crunching underneath my tires told me that there had been a good freeze overnight. I unloaded my sled, and headed up the road, struggling to keep the engine cool even with my scratchers down. I had to stop and pack the tunnel with snow a few times and I felt comfortable knowing that wet loose problems were unlikely at the moment. 

When I got to where I planned to park my sled, I transitioned from a sun-baked slope to a colder, shaded slope. Immediately, I noticed the character of the snow beneath me change. Instead of riding on top of a firm, icy crust, I felt the track of my sled dropping into weak, sugary snow. I parked my sled and stepped off, immediately sinking straight to the ground. "So this is the weak snow that Chris was writing about in the forecast," I thought to myself. I'd found one of the ingredients for the persistent slab problem. These types of avalanches are unpredictable and the best management strategy is to avoid terrain where the problem exists. I'd already decided that morning to do just that.

Skinning up the drainage, I found that slopes that faced the sun were free of snow. No avalanche problems here. On the other side of the drainage, weak sugary snow made up almost the entire snowpack. As I climbed in elevation, the amount of new snow increased and I felt the snowpack collapse underneath me in a number of places. Persistent slab problem located. I stopped to dig a pit and perform some snowpack tests. I stepped out of my skis and sunk through four feet of snow to the ground. A weak snowpack indeed! My snowpit tests yielded unstable results, confirming my earlier decision to avoid slopes where a weak snowpack existed below the slab of recent snow.

I readied myself to head down, choosing low angle terrain to avoid the persistent slab problem. The sunny slopes I encountered had softened a bit, providing some good corn skiing. Fortunately, I'd left early and was getting out of the mountains early, and in doing so I avoided the wet loose avalanche problem. Another good, safe day in the hills.

 

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