Avalanche forecast

Tetons

Bridger-Teton Avalanche Center
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Avalanche danger

Wed
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
2 · Moderate
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Out of date — this forecast expired 3 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

Avalanche conditions remain 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. 

Avalanche problems

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    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 

    (2/27/2023)

    Storm slab avalanches failing within the newest snowfall on 2/27/2023.

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    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.  

     

    (2/25/2023)

    Recent Rendezvous Peak avalanche; this thing just won't stop avalanching. Winded areas harbor shallower snowpacks, weaker snow, and more avalanches. 

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    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.

    Avalanches triggered on this layer have the highest concentration on the southern half of the compass. (Wolf Trap, No Name Canyon, Nugget), and frequent-flyer paths are flying. Wind-loaded terrain will also have an increased likelihood of triggering this weak layer. 

    ADDITIONAL DISCUSSION

    Yesterday, skiers in the Northern Tetons reported widespread collapsing and sensitive conditions at lower elevations.  Multiple human-triggered avalanches have been reported on buried weak snow across the lower elevations. Many of these slopes held weak snow--and that's it--until recently. Steep terrain is avalanche terrain and should be assessed as such regardless of elevation. 

    (2/26/2023)

    Crown an explosive-triggered avalanche at Targhee which failed on a crust facet combo.

    Photo: Dan Nagy

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 (small facets and/or facet+crust sandwich known as Feb. 18 layer, buried about 60+ cm deep), and 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.

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