Bollettino valanghe

Galena Summit & Eastern Mtns

Sawtooth Avalanche Center
Vedi sulla mappa

Pericolo valanghe

Sun
Alta quota
3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
3 · Marcato
Open full map
Non aggiornato — questo bollettino è scaduto 3 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

The snowpack is fragile, complex, and unstable — treat it with respect and build wide safety margins into your travel plans. In the past week, many large human-triggered and natural avalanches were reported, and triggering a large, destructive avalanche remains uncomfortably likely today. Warm temperatures and periods of sunshine will bring wet snow problems to the table. Smaller natural and human-triggered slides can step down to deeper weak layers in the snowpack, resulting in much larger avalanches. 

Problemi valanghivi

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    1.5–3

    Snowfall in January built a hefty, 1-2 foot thick slab over an impressively fragile weak layer. In wind-loaded terrain, the slab may be twice this thick. This combination of slab + weak layer exists on most slopes and has produced countless avalanches in recent days, including a number of large, remotely triggered slides. Dig down and you'll find a layer of snow that resembles an early-season weak layer here: thick facet stacks on slopes that face away from the sun, crusts with associated facets on sunny slopes, and a good helping of surface hoar sprinkled in. 

    Avalanches that fail on this layer of snow will break widely and can be triggered from long distances away from the slope that slides (remote triggering). Small avalanches involving snow near the surface can step down to this weak snow, producing a much larger avalanche.

    At the base of the snowpack, you'll find another layer of weak snow. While less likely, avalanches that step down to this weak layer will involve the entire snowpack and are likely to be unsurvivable (video).

    This enormous avalanche failed above the N Fk of the Big Wood River. The set of crowns that produced it spread across over a mile of terrain and these slides deposited debris in 4 separate alpine bowls. Based on the location and the appearance of the crown, these slides likely failed on a crust with associated facets. The crown pictured here faces SE-S-SW between 9,300 and 10,000'.

  • Wind Slabs

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

    Expect to encounter a range of smaller avalanche issues in the upper snowpack. Warm temperatures and rain will bring a range of wet snow issues to lower elevations and to slopes that directly face the sun. If the snow you are moving through is moist and you can easily make a snowfall, be alert to these types of slides. As you climb higher into colder, windier terrain, look for small fresh cornices and wind slabs. Steep slopes that haven't been affected by the sun can produce dry loose avalanches. All of these problems are likely to be small but can be effective triggers for much larger avalanches failing on the weak snow buried in the snowpack. 

Avalanche Discussion

In recent days, the Forecast has been roughly divided into near-surface and older snow categories. The old snow box (Persistent Slab) isn't going anywhere and continues to be our primary concern. However, warm temperatures and rain are changing the nature of the problems that you'll encounter in the upper snowpack. As the snow at the surface melts, small wet snow avalanches will make an appearance. Initially, these aren't likely to be large enough to bury you, but they can knock you off your feet and push you into places you don't want to go. Small loose snow and wind slab avalanches can step down to the persistent weak layer in the snowpack, producing much larger and more destructive avalanches. These same conditions are also changing the properties of the slab that is sitting on our problematic weak layer. This is a much more difficult process to forecast and the result of this surface warming are uncertain. However, we do know that the snowpack doesn't appreciate rapid change and is about to be subjected to a major meltdown that will play out over the coming days. 

The snowpack varies across this zone, but the theme of instability rings true across the board. The southern end of this zone (Pioneer Mtns) has received the short end of the snowfall stick this season. Snow depth increases as you travel north through the Boulder Mtns, the Baker Creek and Galena Sumit areas, and into the White Clouds. The weak layers described above exist in all of these ranges, but the overlying slab thickness increases as you travel north. The slopes surrounding Galena Summit have produced many avalanches this season already, often occurring in locations that infrequently avalanche. As you gain elevation you'll find increasingly thick slabs that have been stiffened by the wind. You can make very large avalanches here, the type that break hundreds to thousands of feet wide. Be suspicious of steep, snow-covered slopes at all elevations.

So how do we manage this problem? Travel through the mountains knowing that you can make large avalanches in many locations. And that the type of slides you make will surprise you. You may find and trigger avalanches in places where you have never seen them before. Or you may see slides breaking much wider than you might expect. Head into the mountains expecting the unexpected today. Start with a conservative plan and stick with it. 

Regioni coperte