Lawinenlagebericht

Tetons

Bridger-Teton Avalanche Center
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Lawinengefahr

Thu
Hochgebirge
2 · Mässig
Waldgrenze
2 · Mässig
Unterhalb
1 · Gering
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Kernpunkte

Avalanches are most likely on slopes where the wind has built slabs on top of weak layers in the snowpack. Slabs failing on weak layers in sheltered terrain are less likely but can't be ruled out entirely. One way to reduce your risk is to avoid thinner areas in the snowpack at middle and upper elevations. 

Lawinenprobleme

  • Wind Slabs

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

    Observers across the forecast area reported sensitive wind drifts yesterday, and a handful of small natural wind slab avalanches occurred. The wind has eased over the past several days, but many of these wind slabs will remain reactive to your weight today. Wind-affected areas can be identified by pillowed drifts or dunes, cornices along ridge crests or running down sub-ridges, and/or stiffened snow surfaces.

    These wind slab avalanches are likely to be on the smaller side, but if you find yourself in wind-loaded terrain, you're also in an area where you're more likely to trigger a persistent slab avalanche (Problem #2 below). Steep slopes where these problems overlap are where you're most likely to get into trouble. Wind-affected snow may also be buried beneath recent, lighter snowfall. Slopes with stiffer snow near the surface—whether from wind-loading or "spin drifting" below large cliff faces—are more likely to produce big avalanches than areas where the surface is loose powder.

     

     

     

    (1/17/2023)

    Small wind slabs triggered in Chicken Scratch (NE aspect off of Mt. Glory in the Teton Zone). 

    Photo: L. Wolfe

  • Persistent Slabs

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

    Certain aspects and elevations have remained in the sweet spot for hosting a lingering persistent slab avalanche problem that has ebbed and flowed over time. Most of these shallower areas just gained a significant slab due to snowfall and wind changes over the past two weeks. In these locations, the weaker snow near the base of the snowpack is well-developed and exists in a continuous layer. The slab overlying this weak layer is thinner relative to other aspects and elevations and has remained so for a longer period of time. This makes it easier for you to trigger. For these reasons, triggering an avalanche that fails on this weak snow remains a possibility today.

    Over the past week, we've been seeing older snow layers become reactive once again in the middle and upper elevation aspects ranging from east-south-west across the compass. Yesterday's crown on Albright revealed a taper from one foot to around five feet. We can see that the snowpack structure isn’t great in these areas and has remained so throughout the season, but we can’t predict exactly when or where you might affect the weak snow underneath. Probing for changes in snowpack depths on these aspects, looking for visual clues as to shallower snowpack, and digging are some of the ways to assess this dragon. When in doubt about the structure of the snowpack you are riding, choose terrain that is less than 35-45 degrees of steepness.

    (1/16/2023)

    This avalanche was triggered on a west aspect off of Albright Peak around 10,200 feet.

    Photo: C. Martin

Avalanche Discussion

Avoiding avalanche terrain is pretty simple. Deciding when and where to engage with avalanche terrain is very complex. We have patterns of weak snow and slabs that vary widely by aspect and elevation and between forecast zones. If you want to completely avoid areas where weak snow exists you will have to do quite a bit of thinking, planning, and checking snow in the field. The likelihood of triggering avalanches on these weak layers is tricky, particularly with the loading pattern of incremental snowfall discussed in yesterday's forecast.  When you're out in the mountains today, think about the trends we've been seeing with recent deeper activity rearing its head once again, and whether this combination of weak layers and slab exists in the terrain you are in. In many places, you can confirm whether or not that weak snow exists by probing the snow and digging any sort of test pit. The danger may be moderate in all of our zones, but the snowpack is different everywhere you go. Whether or not you choose to enter avalanche terrain is up to you, just be sure you know what sort of dragon you are choosing to engage with. Personally, anytime I'm skiing in the Intermountain West mid-winter, I assume there are dragons everywhere until I gather enough data and see enough of a trend to confirm otherwise. You can significantly decrease your risk by choosing to avoid the terrain where certain dragons live. Here, that means avoiding terrain where the wind has either built drifts or stripped areas so that they've remained thinner until recently-and terrain where weaker snow from November makes up the base of the snowpack.

Remain wary of entering avalanche paths in this zone that have most or all of the following characteristics:

  • Wind-affected alpine or near-treeline terrain above about 9000' in elevation. This does not exclude predominantly windward slopes. These areas have seen recent consistent snowfall and differing wind patterns that have created a complex pattern of scoured and loaded slopes, likely resting on a far thinner snowpack relative to other slopes in the area. 
  • Slopes with rocks poking through the snow and variable snow depths due to uneven terrain
  • 35-45 degrees in steepness
  • On the southern half of the compass (east-south-west)

 

 

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