Avalanche forecast

Tetons

Bridger-Teton Avalanche Center
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Avalanche danger

Sun
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
2 · Moderate
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Highlights

Human triggered avalanches remain possible at all elevations today. Fresh wind slabs near ridgelines and start zones as well as avalanches failing on buried weak layers on the southern half of the compass are the primary concerns. The avalanche danger could rise to Considerable on steep slopes that receive direct sunlight and have been recently wind affected. Pay attention to cracking within wind drifted snow and monitor the effects of the sun today.

There were two avalanche involvements this week involving burials, one of which was critical with a fatal outcome. You can find details here. Our sincere condolences go out to the friends and family for their loss.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–1.5

    Fresh wind slabs near ridgelines and start zones will be reactive to human triggering today. If triggered, soft slab avalanches up to size 1.5 will be likely in lee terrain with slope angles nearing 40 degrees. Old stubborn wind slabs from the February 19-23 storm cycle exist in the alpine in isoloated areas. 

    Pay attention to signs of instability such as cracking within wind drifted snow and monitor slope angles. 

    Dry Loose: Dry loose avalanches are a concern in very steep, rocky, sunlit terrain today. Monitor the effects of the sun today.

    (2/23/2023) Starting zone, with ski tracks (up & down) on ridge to looker's Left

  • Persistent Slabs

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

    Stubborn slabs that are both soft and hard could be triggered by humans today in specific locations. Slopes in excess of 35 degrees on the southern half of the compass are the most suspect, especially near rocky outcroppings and unsupported terrain features. 

    Weak faceted snow and slick crusts exist at both the Feb 18 and Jan 26 interface.  The Feb 18 crust/facet combo is buried 30-60 cm below the surface of the snow on West through South through East aspects at the middle and upper elevations. The Jan 26 crust/facet combo is buried 60-90 cm below the surface of the snow on southerly aspects. Triggering avalanches from a distance (remote triggering) is possible but unlikely. 

    Pay attention to signs of instability such as audible collapsing of the snowpack and monitor the effects of the sun on the snow surface today. Your best line of defense against a persistent slab problem is to dig a snowpit in a representative location and perform some stability tests such as an Extended Column Test. 

    (2/23/2023)

Avalanche Discussion

More snow and wind for the Tetons. Fresh wind slabs are on the menu. Persistent slabs are still in play at all elevations. Today will be the first sunny day since the last major storm event and there is fresh, light powder to be found. What role will human factors play today?

The Tetons picked up 30 to 40 inches of snow from February 19-23. Westerly winds prevailed at the beginning of the storm cycle but veered to the North and eventual the East by the end of the cycle. This has resulted in wind slabs that are generally 18-24 inches deep on a variety of aspects at the upper elevations, but could be up to 3 feet deep in favored locations. On the northern half of the compass these slabs are failing on a density change within the new snow or on the new snow/old snow interface (Feb 18). On the southern half of the compass these slabs are failing on a slick crust at the new snow/old snow interface (Feb 18). These slabs could be both soft (4f) and hard (1f). Wind pressing from easterlies at the end of the storm as stiffened slabs on unusual aspects. 

Recent avalanches have been observed at all elevation bands on a variety of aspects up to size 2. These avalanches have failed within the new snow and at the new/old interface. Avalanches involving older buried weak layers have occured in the Greys River Zone and near Snow King within the last 2 days. In my mind human triggered avalanches will most likely occur near the new/old interface on North and East aspects (slab depths 18-24 inches, possibly deeper). On southerly aspects failure at the Jan 26 interface remains a very real concern, especially at the middle elevations (slab depths 18-24 inches but could be deeper).  As is common in the wake of windy storms in the Tetons, avalanches starting below traditional starting zones ( i.e. below cliff bands) need to be considered. 

The new snow/old snow interface lies 30-40 cm down on the southern half of the compass and closer to 60 cm down on the northern half of the compass. This interface is a crust on southern aspects and near surface facets on northern aspects. The January 26 crust/facet combo lies 60-80 cm below the surface of the snow at upper elevations on the southern half of the compass. The last known human triggered avalanches associated with this layer in the Tetons occured in the wake of the major storm event at the end of January and early February, but some of the recently observed avalanches in the Greys River Zone and at Snow King have raised our hackles. The November 27 layer generally lies 1-2 meters below the surface of the snow at upper elevations on the southern half of the compass. The last known human triggered avalanche associated with this layer was on January 16.  

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