Bollettino valanghe

Salt River and Wyoming Ranges

Bridger-Teton Avalanche Center
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Pericolo valanghe

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

In sintesi

While a significant storm event has ended, conditions remain dangerous. Avalanches are most likely on slopes with wind drifting but could occur in wind-sheltered terrain. Triggering a larger avalanche breaking deeper within the snowpack is becoming less likely, but still poses a real threat. Safer conditions—and the best riding—can be found on gentler slopes (<30°) sheltered from the wind.

Problemi valanghivi

  • Wind Slabs

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

    Close to a foot of new snow over the last 48 hours, with moderate to strong west/southwesterly winds. As a result, wind slabs have formed on the lee sides of ridges and other exposed terrain features. Warm temperatures at the start of this storm period have helped these wind slabs bond to underlying snow surfaces, but more snow and wind today will create a fresh batch that may be sensitive to your weight. Several storm interfaces due to shifting temperatures exist in the upper portion of the snowpack; these layers are more challenging to identify and are less evident than a prominent weak snow layer.

    The best way to avoid this problem is to avoid steep slopes or consequential terrain where you find indications of recent wind loading. Watch for snow that is denser than snow found on wind-sheltered slopes and tell-tale clues such as surface texture and a pillowed, drifted appearance. Yesterday, a rider was fully buried in the Palisades but was fortunately rescued, and the group was able to self-extricate. These avalanches were reported 48 hours ago near Commissary Ridge. 

    Safe travel practices are necessary: good comms, checking out the snow you're riding (particularly north-facing terrain on even small but steep terrain features like those above creekbeds), steering clear of terrain traps, moving one at a time, and not exposing multiple people to steep slopes. 

    (12/28/2024)

    A recent slab avalanche in the Mink Creek Drainage near Commissary Ridge.

    Photo: Kelly Corgiat

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–2.5

    Weaker snow layers now buried 3-4+ feet deep have not gone away, but they've become less reactive to the weight of a skier or rider. Due to their depth, they've also become very difficult to impact with your weight. Bear this weak snow in mind—especially since the consequences of triggering a large persistent slab increase as more snow has fallen. This problem is most prominent on steep (>30°), north-facing alpine terrain and areas more likely to have thin spots where your weight may reach the weak layers. A conservative travel plan is a good idea today, given the uncertainty associated with the buried weak layers deeper in the snowpack.

    (12/20/2024)

    This persistent slab avalanche was remotely triggered up Murphy Creek near the Stewart Massive on a NE aspect around 8300' on 12/20. 

    Photo: Bridger-Teton Avalanche Center

Avalanche Discussion

FAQ's regarding the current snowpack

Q: How do avalanches fail on storm layers...and why?A: Multi-day storms like the one we're experiencing produce a variety of different snow crystal types. Some of these types don't get along very well and can behave much like a persistent weak layer. Like surface hoar, they're slippery. When these crystals are buried, they can remain preserved for longer than we expect and cause avalanches to fail within the new snow or at an interface between the new/old snow, particularly if storms start cool and end warm. Fortunately, the snowfall last evening did just that; however, weaker snow remains preserved in the upper portion of the snowpack from snowfall over the past 72 hours. Storm layers can be tricky, more challenging to identify, and capable of surprisingly wide propagation and remote triggering.  Expect to be surprised and build some safety margin to account for this uncertainty. 

Q: How do persistent weak layers like basal facets or buried surface hoar heal?A: One way is through mechanical compaction or compression. When a very thick, dense slab overlies a weak layer, the sheer weight of the slab begins to squash the weak layer. Like a group of introverts at a social gathering, at some point, they have no choice but to begin to connect. We're just starting to see this mechanism in some places where the primary weak layer near the bottom of the snowpack is showing signs of relenting under the weight of a thick slab. This layer remains shallowly buried and more developed in other areas (primarily the north half of the compass, rocky, or alpine terrain). As snow stacks up, these are the spots to keep on your radar. Continually probing the snow and looking beneath the surface to observe the snow you're riding is the only way to assess this problem and track it over time. 

Thank you to all who have contributed observations during this cycle. This allows everyone to gain a better and more complete understanding of conditions. You can submit observations and photos HERE or text 307-264-3050

 

 

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