Avalanche forecast

Tetons

Bridger-Teton Avalanche Center
View on map

Avalanche danger

Fri
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
1 · Low
Open full map
Out of date — this forecast expired 3 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

The potential remains to trigger wind affected snow today, particularly along ridgetops and in steep gullies.  The lingering threat of triggering a much thicker slab avalanche on a deeply buried persistent layer also exists today.  Riding and skiing on a thicker snowpack unaffected by the wind and off of steep and rocky terrain will greatly reduce your chance of triggering an avalanche.

Two cornice failure incidents occurred yesterday, one of which resulted in a significant fall. Cornices are large and sensitive to triggering right now.

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1.5–2.5

    This zone has persistent weak layers buried 3-5 feet deep on most middle and upper elevation slopes on the north half of the compass. Feedback in the form of avalanches on these layers has been rare and unreliable but recent large avalanches, such as the cornice fall yesterday at Targhee and the very large avalanche last Saturday on No Name Peak, make it clear that these layers are still a potential problem.  Look for clues to help you avoid the thin spots where your weight could trigger a weak layer. Spending time beneath a corniced ridge is also not a good idea. You can further reduce your exposure to this problem type by:

    1. Choosing moderate slopes with low consequences. Safer travel options always exist by sticking to slopes less than ~30 degrees.
    2. Avoiding shallow areas. The weak layer is more easily triggered where it is closer to the surface. The thinner edges of slabs are often the trigger point for much thicker slabs.
    3. Avoiding terrain where wind slabs sit on persistent weak layers. Triggering a wind slab or cornice significantly increases your objective hazard and will more easily impact deeper layers. 

     

    (2/17/2024) Photo: Teton County SAR

    The avalanche on No Name peak is a reminder of the destructive power of an avalanche failing on a deeper weak layer. This one required a very large trigger - either a cornice fall or possibly a smaller avalanche. Steep, rocky terrain like this is a breeding ground for this type of avalanche.

  • Cornices

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–2

    Light density snow and moderate wind speeds have built very large, overhanging cornices that are becoming more sensitive to triggering in the warm temperatures.  Two incidents occurred yesterday near Grand Targheeand in the Big Holes. Give cornices a wide berth, more than you think, and look for rocks and brush underfoot to confirm that you have solid ground beneath your skis or sled. Cornices can break further back than might expect. They can also serve as the heavy trigger needed to impact a deeply buried weak layer. 

    (2/21/2024)

    Cornice failure at the top, crowns in the center, flanks below the cliffs outlined in blue.

    Photo: Daniel Nagy

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–2

    Multiple wind slabs were triggered several days ago.  These slabs have gained stability and become much less reactive since that time. The recent avalanches occurred in exposed upper-elevation and north-facing terrain along gullies and aprons. On southerly aspects, these slabs will be on top of a mix of crusts, and on northerly aspects, a thin layer of facets exists at the old snow/recent snow interface.  Smaller wind slab avalanches have the potential to step down to more deeply buried weak layers and produce a much larger avalanche. 

    (2/19/2024)

    Wind pockets will vary in size and distribution at upper elevations in the Tetons. Choose terrain accordingly, and consider the consequences of even a small slide that rips in an unexpected way. 

Avalanche Discussion

Avalanche forecasts become overly complicated and difficult to apply to terrain choices when there are multiple avalanche problems listed. Cornice fall appeared on the list of problems today in order to highlight an issue which has been discussed from time to time in the wind slab avalanche problem. Cornices are not difficult to identify and avoid, but can be unpredictable in the ability to cling to steep terrain. Most of the time they aren't a widespread problem until significant warming. The two incidents yesterday and maybe the very large avalanche on No Name over the weekend may be a trend towards a wider problem, or maybe these incidents are a coincidence. In any case, these cornices have grown large this season and are a growing concern and will likely continue to be another low probability, high consequence hazard to keep on your radar.

As the sun's azimuth angle continues to increase, brief periods of sunshine  decrease the stability of the snowpack and relatively warm air temperatures do the same.  The period of unsettled weather this week that will persist through the weekend brings the chance of clearer skies than forecast. Keep track of this solar gain when you are out and about. While it doesn't seem likely that we'll see wet avalanche activity given the forecast, direct sunshine or greenhousing can decrease stability quickly though temporarily. 

Regions covered