Bollettino valanghe

Tetons

Bridger-Teton Avalanche Center
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Pericolo valanghe

Thu
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
1 · Debole
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Non aggiornato — questo bollettino è scaduto 4 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

To significantly reduce the odds of triggering a large avalanche, avoid steep, open slopes that are exposed to the wind. Look for evidence of recent wind loading such as cornices, pillows, and drifted snow. While unlikely, it remains possible to trigger a large, 3-5 foot thick avalanche—especially on steep, rocky, wind-affected slopes. 

Problemi valanghivi

  • Wind Slabs

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

    The combination of new snow and wind has built slabs in terrain where the wind blows. I say this because as we know, this means many different features in the middle and upper elevations, and sustained west/northwest winds can craft slabs in abnormal locations.  Continued wind transport was observed yesterday above 9,000 feet in the Tetons. I'd expect fresh wind slabs to be on the smaller side, but given the weak snow surfaces they're forming on, they may remain sensitive to your weight. Recognize that wind-loading also adds stress to the weak layers buried in the snowpack (described in Problem 2 below). Any wind slab you trigger could step down to these deeper layers, producing a much larger, more dangerous avalanche. While come of these new slabs may remain small, they may be able to pick up steam as they travel downslope. Even small slides can have high consequences if they carry you through rocky, treed terrain.

    The new and wind-transported snow from the past 24 hours is now masking older wind slabs that formed earlier in the week. These older wind slabs have likely had time to stabilize, but given the increased chances of triggering a larger avalanche on wind-loaded slopes, it is prudent to avoid obviously wind-loaded avalanche terrain. 

    (1/23/2023)

    This wind slab avalanche in Crooked Thumb Basin entrained a larger amount of new snow and traveled over consequential terrain. This illustrates the importance of choosing terrain wisely with both wind slab and persistent problems. 

  • Deep Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Unlikely
    Dimensione
    2–3

    As days with small amounts of new snowfall continue to trickle in, the snowpack is getting time to slowly adjust to additional loading.  However, the possibility of triggering a slide on a deeply buried persistent weak layer will be on the table for some time to come. Uncertainty is high as to the tipping point of these layers. If you choose to enter avalanche terrain, be aware that at least one of these layers likely exists in the snowpack underneath you, particularly if recreating in terrain in the middle and upper elevations and on the southern half of the compass. Though not widespread, the layers most likely to produce large avalanches in this zone are found 2-5 feet deep consisting of well-developed facets near the base of the snowpack and crust+facet sandwiches. These prominent early-season facet layers are buried deeply in some areas, making it much more difficult, but not impossible, to trigger. 

    In a nutshell: be alert to the consequence of being caught in a large avalanche in the terrain you are recreating in. 

    You are more likely to trigger an avalanche on upper elevation, "prime-time" slopes steeper than about 35 degrees. Most upper-elevation slopes have received additional loading due to wind over the past few weeks. While triggering a wind slab (Problem #1 above) is more likely, a wind slab avalanche could step down into these persistent weak layers resulting in a much larger avalanche.

    (1/20/2023)

    Snow pit on Prospector's Peak showing moderate strength (ECTP14) and continued sensitivity on facets buried Nov. 27th. 

Avalanche Discussion

Gather Evidence and Play the "What-If" Game

We're in an interesting time with daily incremental snowfall, new slabs forming on some weak surface snow, and the Teton trickle continuing to possibly tickle deeply buried weak layers. I'm interested in seeing what flushes out with a bigger storm this weekend. 

A low-frequency, high-consequence event is one of the most difficult problems to manage. By definition, it lies on the edges of our experience. Talk to your partners, communicate with other parties you encounter, and poke holes in your theories to not limit yourself to the obvious. Taking a broader approach to problems and solutions will set you up for mitigating uncertainty and the consequences that come with it. I constantly play the "What If" game in avalanche terrain. What if this slid? How bad could it be? What evidence do I need to know that I'm not just propagating errors in my thinking about this avalanche problem? Uncertainty can act as a guide for your plan for gathering observations while in the backcountry. Ensure the evidence you're gathering actually helps reduce your uncertainty about a problem and doesn't just support a desire. At the end of the day, a slope full o' tracks is just that-- a slope full o' tracks, and not a stability pattern. 

Another guiding question I read recently in a neighboring forecast zone is this: "Sure, avalanches are still possible, but where are they most possible?" Nearly all of this season's natural and human-triggered avalanches have occurred on a) steep terrain, b) ranging on the southern half of the compass, and c) wind-loaded slopes. Avoiding these types of slopes means you avoid areas where avalanches are "most possible." 

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