Lawinenlagebericht

Salt River and Wyoming Ranges

Bridger-Teton Avalanche Center
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Lawinengefahr

Thu
Hochgebirge
3 · Erheblich
Waldgrenze
2 · Mässig
Unterhalb
2 · Mässig
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Veraltet — dieser Lagebericht ist 4 years ago abgelaufen. Du siehst vergangene Verhältnisse, nicht den aktuellen Bericht.

Kernpunkte

Triggering a large avalanche is likely on steep, wind-drifted slopes. This possibility also exists on upper-elevation slopes that are sheltered from the wind as new snow will sluff easily on crusts formed in some areas of this zone. Additional snowfall is adding weight to buried weak layers in the snowpack. Some of these layers may be in the middle of the snowpack and some may be near the ground. Reduce your risk by sticking to lower-angled terrain that is sheltered from the wind. This zone is large and incredibly variable. Cautious route-finding and conservative decision-making are essential, particularly in upper-elevation terrain or on any shallower slope. 

Lawinenprobleme

  • Wind Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Likely
    Größe
    1–2

    The weight of new snow is adding stress to a variety of weak layers in the snowpack. This stress is amplified in areas where dense, thick, wind slabs formed during recent strong wind. Our most concerning persistent weak layers sit near the middle of the snowpack. An avalanche failing on one of these layers has the potential to be very large, particularly in open and well-connected terrain features. Two ways to manage this are:

    1. Avoid trigger points and shallower slopes (south and east aspects). You’ll be most likely to impact these deep weak layers in areas where the snow cover is thin, like near rocky outcrops. Heavily wind-affected areas where the wind has created a patchwork of scoured and loaded slopes are also more likely to be problematic.
    2. Keep an eye on the terrain you are traveling through and underneath. Avalanches are most likely on slopes between 35-45 degrees of steepness, however, persistent slab avalanches can be triggered remotely — from below or to the side of steeper slopes. 

    ADDITIONAL DISCUSSIONYesterday’s storm brought 6-10” of new snow to this zone. Remote weather stations indicate that wind speeds have remained light through this storm and I expect any wind slabs that you might encounter today will be isolated to exposed, upper-elevation terrain. These slabs are likely to be more touchy where they are sitting on icy crusts or slick surfaces.

  • Persistent Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    2–3

    The weight of this new snow is adding stress to a variety of weak layers in the snowpack. This stress is amplified in areas where dense wind slabs may form today.  

    Our most concerning persistent weak layers sit near the middle and base of the snowpack. An avalanche failing on one of these layers has the potential to be very large, particularly in open and well-connected terrain features. Persistent weak layers are difficult to deal with. They can produce avalanches many weeks after they are buried and they provide fewer and fewer obvious signs of instability as the days without a significant loading event pass. They can break wider than you might expect and may be triggered remotely, from gentle terrain adjacent to steeper slopes.

    Digging a snowpit in one location may not identify these layers, but will clue you into what the overarching structure at a certain aspect or elevation may look like. Broadly, the snowpack structure is poor here, and use extra caution, even in terrain sheltered from the wind, where weak structure (any harder snow + softer snow underneath it) exists.

    (1/5/2023) Photo: Antonioli

    Persistent slab avalanche in the Wyoming Range. 9500' SE aspect

Avalanche Discussion

Feedback

Hopefully, we’ll have a larger body of evidence to pull from after this series of storms in the Greys River zone. I say “hopefully” because there’s an overarching "I guess we’ll wait and see if certain things avalanche naturally” mentality leading up to this storm. It’ll be interesting to see what slides and what doesn't, of course, a lot of this activity is tied to how much snow we get, where it falls, and how fast. Given the spatial variability of the current snowfall, snow depths, slab properties, and weak layers, the outcomes may vary drastically over a short distance. While these weak layers are put to the test, take a big step back and record what you see—the next several days could be interesting.

In the Greys Zone over the past week, I've found snowpack depths ranging from 12 inches to over 3 feet deep; one sub-zone had widespread melt-freeze crust from a recent clearing above 9,000 feet, even on northerly and shaded aspects, while another held soft, dry snow still even in the lower elevations. I've found buried surface hoar, thick layers of facets in the middle and base of the pack, and also thick crusts at the base of the pack with very little facet development-literally every condition in the book. Microclimate zones exist within each larger range (whether it's the west vs east of the Tetons, the differences along the Continental Divide at Togwotee, or the Salt Range vs Wyoming Range of the Greys), and each is worth getting to know closely if you are frequenting it.  With any snowpack, it's very important to recognize when you are dealing with a problem that is more complex than we as humans can typically fully understand. We can still make our best assessment with all the tools available to us, and our best bet is to always step back if surprised by something. Pad your uncertainty by building healthy margins for error into your travel practices, and tread lightly with rapidly changing snow conditions today.

 

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