Avalanche forecast

Snake River Range

Bridger-Teton Avalanche Center
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Avalanche danger

Thu
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
1 · Low
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Highlights

Recent wind slabs are becoming stubborn. However, the possibility remains of triggering an avalanche 1-2 feet thick on very steep wind loaded slopes above 9500 feet. Look for signs of wind loading and recent avalanches. Buried weak layers remain an unlikely threat but will cause large and destructive avalanches if triggered. Evaluate steep and shady slopes carefully above 8500 feet for deeper instabilities.

Avalanche problems

  • Wind Slabs

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

    It is becoming unlikely that you will trigger a wind slab. The likelihood will continue to decrease as we get further from the last loading event. However, there may be lingering slabs up to 2 feet deep at upper elevations in very steep terrain. Wind slabs from several days ago formed on multiple aspects from shifting winds. Continue to pay attention to very steep slopes below ridges, rocky outcrops, cliffs, and cross-loaded gullies.

    Very steep middle and upper elevation sunny slopes could warm quickly today with a temperature inversion in place.  Look for moist surfaces and rollerballs. Watch for overhead hazard on very steep sunny slopes with rocky outcrops, where shedding snow could entrain enough snow to knock you off your feet.

    A skier triggered avalanche on No Name Peak on Dec 28th resulted in the skier being caught and carried but not buried. 

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely
    Size
    1.5–3

    Weak layers exist in the snowpack throughout much of the forecast area. It is unlikely that you will impact these layers and cause an avalanche, but it cannot be ruled out. If triggered, avalanches will be 3-6 feet thick, very large and destructive. Slopes that face north through east at middle and upper elevations are the most concerning. Triggering is more likely if you find a thin spot in the snowpack or have a large enough trigger - like smaller avalanches that step down or cornice falls. Give yourself a margin around steep, northerly slopes.

    A very large persistent slab avalanche in the north fork of Mosquito Creek. This avalanche included the entire snowpack and likely ran late 12/27 or early 12/28. 4-5 feet deep.

    NE facing at 8,900'

    Photo: Bridger-Teton Avalanche Center

Avalanche Discussion

If you take a quick look at recent avalanche observations, the last avalanche cycle paints a clear picture - a surface instability problem (wind slabs) and a specific persistent slab problem. The latter might be worth discussing. Weak snow from November is sitting at the bottom of the snowpack. Above that basal weak layer sits a hard crust buried in mid-December. These layers remain a concern above 8500’ on multiple aspects. Several very large and destructive avalanches occurred in the Tetons and Snake River Range at the tail end of the recent storm system; No Name Canyon, North Fork of Mosquito, Powder Corn, Starvation - to name a few. These avalanches ran either on the ground or in deep weak layers, were all large and destructive, and illustrate the unpredictable nature of a persistent slab problem. We’re just never quite sure when they will occur or how much loading it will take to tip the balance. The last of these big avalanches most likely occurred around the 27th or 28th, and since then, a lack of any new loading and cooling temperatures has helped the snowpack to begin the adjustment process. 

These avalanches are all very specific to steep slopes above 8500’ on north through east aspects with wind loading (large trigger). This information gives us guidelines for where (and where not to) travel as the snowpack continues to adjust. While it is unlikely that you will trigger one of these large persistent slab avalanches, we can’t quite rule it out. Carefully evaluate steep middle and upper elevation slopes facing north through east. Give yourself a margin if there is any wind loading in the start zone. There will likely NOT be any signs of instability until it is too late and you are out on a slab and trigger an avalanche. The likelihood is low, but the consequences of this type of problem are high. Without any clues to indicate weak snow, we ultimately manage this problem by avoiding steep shady slopes while the snowpack adjusts.

Happy New Year, everyone!

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