Bulletin d’avalanche

Tetons

Bridger-Teton Avalanche Center
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Danger d’avalanche

Sun
Alpin
3 · Marqué
Limite forestière
2 · Modéré
Sous la limite
1 · Faible
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Points saillants

The combination of recent snowfall, wind, and buried weak layers make human triggered avalanches likely at the upper elevations today. Steep and rocky terrain where the wind has stiffened the snow into slabs is of primary concern. Cracking within wind drifted snow and audible collapsing of the snowpack are signs of instability. Conservative decision making and cautious route finding are advised. 

Problèmes avalancheux

  • Wind Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    1–2

    Wind slabs have formed over the last few days with consistent snowfall and light to moderate winds. With 3-5 inches of snow forecasted and SW winds gusting into the 30s these slabs could be 2-4 feet deep and sensitive to human triggers. Winds are forecasted to peak sometime before noon today before tapering off throughout the rest of the day. 

    There is plenty of snow available for transport from yesterday and the previous storm cycle. In the last 3 days the Tetons have picked up around 17 inches of snow above 9k' with light to moderate winds.  

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    1–2.5

    There are currently 2 major persistent weak layers buried within the top 3-6 feet of the snowpack. These layers are failing in the moderate-hard range in stability tests and have not been showing a propensity to propagate lately. New snow and wind will stress these buried weak layers.

    Weak snow is also present in very steep, rocky terrain. This is especially true in areas that have been affected by previous avalanche cycles this month. 

     

Avalanche Discussion

Yesterday and last night the Tetons picked up an additional 4-7 inches of snow. Most of this snow has fallen with a gradual warming trend, causing the storm snow to be slightly upside down in many areas. In the last 3 days the Tetons have received around 17 inches of snow above 9000' with light to moderate winds. This has led to large amounts of snow available for transport. At 6 am winds on top of Rendezvous are blowing out of the SSW around 30 mph with gusts in the upper 40s. 

Yesterday wind slabs did not seem to be nearly as prevalent as forecasted, at least below 10,000 feet. Reports of drifting and cracking snow seemed to be more common on the SW corner of the range or at the uppermost elevations. At this point it seems like steep, rocky, and shallow areas are the most suspect (typical). South aspects with shallow snowpacks and crust/facet combos have poor structure at the middle and upper elevations but it doesn't seem like the winds have been westerly enough at this point to sufficiently cross load these areas. Winds are forecasted to shift the N on Sunday. 

Avalanche paths that slid earlier in the month at the mid elevations are also an interesting problem. Start zones with northerly aspects around 8800' that avalanched in early to mid December are starting to get built out again. Sloughing in steep terrain and couloirs could also be an issue today.

Observations have been limited from the last few days but no human triggered avalanches have been reported. It is likely that some natural wind slab activity took place some time around the evening of the 28th (associated with AR frontal passage). There were also some reports of stability tests failing on a layer of graupel that fell mid-storm on the afternoon of the 28th. Snowfall and light winds since have conspired to cover up any avalanche activity (if it did occur).

The November 27th layer has been dormant since about December 16. A thin layer of near surface facets that was buried around December 5 seems to be gaining strength as well. 

Régions couvertes