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
2 · Moderato
Sotto il limite
2 · Moderato
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Non aggiornato — questo bollettino è scaduto 3 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

Triggering a large, dangerous avalanche remains likely—especially in wind-affected, upper-elevation terrain. Continued snowfall and strong winds today will create sensitive drifts and add more weight to buried weak layers.  Expect to find these in atypical locations, thanks to the strength and direction of the wind.  Expect hazard to increase throughout the day. The southern portion of the Greys Zone will receive more snowfall today and throughout this evening.

Problemi valanghivi

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1.5–2.5

    Problems #1 and #2 currently have a complex and overlapping relationship. Two primary layers of weak snow exist in the top meter of the snowpack here (and could rest deeper in areas that receive more wind). A natural avalanche on Mt. Taylor likely failed on facets or a crust+facet combination buried from all snowfall accumulated after March 20th. I found this layer on Shadow Mountain on Sunday as well as in the Snake River Range yesterday, however, recent human-triggered avalanche activity has primarily involved a layer of weak snow buried ~ March 30th that is now 2-3 feet deep. Both of these layers have produced failure in snowpit tests and it is worth adding the observation of the activity of both of these layers to your toolkit where you are recreating. Observations are sparse when you put an entire mountain range in viewpoint; both layers of facets seem most common on the middle to upper-elevation slopes ranging NE-E-SE in aspect. We don't often deal with persistent weak layers so late in a season, and it definitely requires a mindset shift. Triggering a 2-3+' thick persistent slab avalanche will remain a possibility this coming week. You're most likely to trigger a slide involving this weak snow on very steep slopes (steeper than about 35 degrees) where the wind has built slabs in recent days and weeks. 

    In areas with a weaker snowpack, such as the Wyoming Range, deeper weak layers still remain a concern. Triggering a wind slab or persistent slab on layers in the upper half of the snowpack could step down to deeper layers resulting in a very large avalanche. 

    (3/28/2023)

    The third rider near or on slope triggered 1' thick soft slab from the diagonal track on the right. The slab slid on a slick crust with small facets on it that was buried March 20.

    Photo: Frank Carus

  • Wind Slabs

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

    Triggering a large avalanche is most likely where the wind has drifted the snow. Today's wind will affect upper-elevation and alpine terrain, and some exposed middle-elevation slopes. Expect to find these slabs in both obvious locations (such as near ridgelines) as well as in atypical locations that are commonly sheltered from the effects of the wind. Slabs also commonly form below cliff bands, on the aprons below steep couloirs, or at the base of cliffs where spindrift accumulates. Watch for evidence of windblown snow such as pillowed areas, dunes or ripples, or denser snow at the surface. Wind slab avalanches could break down into buried weak layers (see below), producing an even more dangerous avalanche.

     

    (3/29/2023)

    Indian Creek Natural avalanche. 9000' NE aspect wind loaded slope failed on March 20th interface

    Photo: Cooper Branham

Avalanche Discussion

It's been a wild ride. Over the past two weeks, our mountains have slowly but surely picked up 2-3'+ of new snow. Cold temperatures have produced uncharacteristically light powder—it's felt more like February than April lately. The final round of snowfall throughout the remainder of this week will deliver several more inches of snowfall, warming temperatures, and strong, gusty winds.  Be prepared to shift your mindset as you head out today and dial back your ambitions through the day as winds increase or if you encounter slabs in unexpected places. The only way to guarantee layers of weak snow won't be an issue is to avoid the terrain where they exist. Unfortunately, that describes a lot of slopes out there. Fortunately, you can significantly reduce your exposure to the hazard by choosing gentler sheltered terrain. 

Frustrated about the complexities of the above problems this late in spring? Don't worry, I'm there with you. One of my favorite things to do is ski avalanche terrain in the spring, and my preference is steep avalanche terrain. But my priority will always be to come home in one piece at the end of the day. Because of the uncertainty associated with these weak layers, I've taken a step back from steep slopes where these weak layers exist, particularly in places that just had a bunch of snow piled up on top of them. There is lots of good skiing and riding to be found in gentler terrain currently. Being exposed to a number of avalanche problems each day, whether at work or play, means that your margins have to be very clearly defined. Thus, though it may not be my first choice for this time of year, it's the only way I can ensure I can head back out again tomorrow. Enjoy another taste of winter, and take some time to think about the range of hazards you'll be facing today.

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