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

In sintesi

Avalanche conditions remain very dangerous. New snow + wind + weak layers in the snowpack = increased likelihood of triggering a large avalanche. Similar conditions over the past few weeks have produced several human-triggered and natural avalanches. Reduce your risk by sticking to gentler slopes, especially those sheltered from the wind. 

Problemi valanghivi

  • Wind Slabs

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

    Fresh wind slabs will continue to form with moderate winds from the southwest at ridgetops. Winds are expected to shift east/southeasterly, so be on the lookout for these slabs developing in abnormal locations.  Yesterday in the Tetons, I found less active wind slab development in the middle elevations than I expected, however, your terrain of choice may dictate where you find this problem. Assume it will be present at upper elevations--but more exposed sections of terrain, rocky features, and saddles and ridges down to the middle elevations may also build some burly slabs today. Slab depths will range from1-2+ feet, and may break on mid-storm interfaces but also hold a higher possibility of breaking on layers deeper in the snowpack.  

     

  • Storm Slabs

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

    With any start-and-stop snowfall or incremental loading, different interfaces will form within said newest snowfall.  Many folks reported slab development in areas sheltered from the wind, and snow skied upside-down--clear indicators of this problem. I suspect it to remain today as intense periods of snowfall continue into the morning. Be on the lookout for surface cracking, even in sheltered terrain, and expect to find this problem wherever the wind has not compacted, primarily at middle elevations and lower elevations.

  • Persistent Slabs

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

    Weather conditions are rapidly changing, and subsequently, as are the avalanche problems dictated by them. Numerous soft and hard slab avalanches have been triggered recently on weak layers buried 2-3 feet across all elevations and most aspects. Additional loading of new snow as this storm cycle continues will add stress to these weak layers increasing reactivity. A primary persistent weak layer of concern, buried Feb 18th, consists of small facets and/or facets+crust. This layer may be hard to find in simple hand pits and is in the top meter of the snowpack, thus is worth digging and checking for.

    This zone is large and snowfall rates for this storm have varied greatly; larger amounts of new snowfall will greatly increase the possibility of triggering a large avalanche here

    Recent avalanche activity, including the unfortunate fatality in Poker Creek, is a clear sign that we need to carefully assess the terrain we enter in the Greys Zone for the remainder of the winter. 

     

    (2/24/2023)

    Poker Creek fatality from a persistent slab avalanche. 8100' NW aspect

Avalanche Discussion

The Thorn (bad news). Over the next few days, we will remain in a very active weather pattern which may dictate much of the avalanche activity we will see--or not see, due to lack of visibility. Incremental loading will test weak snow buried near the middle and base of the snowpack across the Greys Zone. Storm snow may remain sensitive and easy to trigger due to shifts in snowfall and rapid loading. I'm a big fan of sunshine, but any clearings or warming temperatures will come as a shock to the snowpack moving into the next week. Most of our areas have significant amounts of moderate-density snow at the surface. We'll likely see some of this recent snowfall sluffing from steep terrain. Any next longer clearing, we may see a significant "shed" cycle where large amounts of snow come unglued from steep, sunny slopes—especially in areas that received the most recent snowfall. These loose snow avalanches could trigger larger slabs as they run downhill. Another point to consider is that as this new snow settles or warms, this process may add stress to buried weak layers or recent wind slabs, worsening any persistent slab problem. Creepy!

The Rose (good news). This past month has led to a rapidly changing and stressed-out snowpack, but there's been plenty of good riding to be had. Few clearings and sunny days have made for fairly endless and safe pow on many slopes. After the initial effects of this storm, instabilities within the new snowfall will likely taper off quickly.  Any subsequent sunny clearings or warm temperatures will run their first course, and the snowpack will start to get the break it sorely needs. Over time as we transition to spring, warmer temperatures promote the strengthening of snowpack layers. Since the more recently-formed persistent weak layers in the top 3' of the snowpack aren't particularly well-developed there's reason to be hopeful that the warming trend will help these to stabilize. Deeper, more well-developed layers may take more time, however, plenty of great terrain exists that minimizes our vulnerability to larger avalanches breaking on deep layers. 

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