Bulletin d’avalanche

Tetons

Bridger-Teton Avalanche Center
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Danger d’avalanche

Tue
Alpin
2 · Modéré
Limite forestière
3 · Marqué
Sous la limite
2 · Modéré
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Périmé — ce bulletin a expiré 3 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

Avalanche conditions remain dangerous and difficult to predict. Hard slab avalanches can be triggered in very steep terrain. These slabs could be triggered on a variety of aspects and are most sensitive in the middle elevations. Warming temperatures and periods of direct sun will make these slabs more sensitive in the afternoon. Monitor snow conditions as the day warms and make conservative terrain choices to avoid being caught in a large avalanche.

Problèmes avalancheux

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    1.5–3

    It is possible for skiers and riders to trigger large hard slab avalanches failing on weak snow that formed during December. These slabs are 2-4 feet deep above 7,500’ and 1-2 feet deep below that. Most aspects remain suspect because of the widespread nature of the January 4th persistent weak layer. Triggering an avalanche is most likely between 7,500’ and 9,000’ due to a thinner slab and well preserved weak layer, but should not be ruled out on steep slopes at the higher elevations. These slabs will become more sensitive to human triggers as temperatures rise today. A remotely triggered avalanche that occurred two days ago indicates that triggering a slide from a distance is still possible in the middle elevations. Steep, rocky, and unsupported terrain features are most likely to produce an avalanche at the moment. However, given the well connected nature of the weak layer, it is possible for avalanches to propagate long distances across or up slopes. Because of this, careful evaluation of the terrain that you plan to ride, as well as the surrounding slopes is important. Avoid crossing underneath steep slopes, especially this afternoon, and give consequential terrain features (gullies/cliffs) a wide margin.

    Although unlikely, there is a chance that an avalanche failing on the January 4th interface could step down to weak snow at the base of the snowpack resulting in a very large avalanche.

    Additional Discussion

    For those traveling to the highest portions of the forecast zone, beware of shallow (less than 6”) wind slabs that may have formed from the light snow we have received over the past week. These slides will be isolated to very steep, wind loaded features in the upper elevations such as couloirs. A small slide that knocks you off your feet in serious terrain can have severe consequences.

    A remotely triggered avalanche that occurred  on 1/27 outside the JHMR boundary. Note the convex, rocky, and wind affected nature of the terrain.

  • Loose Wet

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    1–1.5

    Temperatures at 8,500’ warmed to freezing yesterday afternoon and stayed warm overnight. Rising temperatures today combined with periods of direct sun will increase the chance for wet loose activity on steep solar slopes and all aspects at the low elevations. Notable wet loose activity was reported yesterday afternoon below 8,500’ near Teton Pass. These slides will be small, but have the potential to knock you off your feet or push you into terrain traps like gullies, cliffs, or trees. Monitor snow surfaces as the day warms and beware of the terrain you travel through and under as you exit from the upper elevations.

Avalanche Discussion

Slab depths from the January storms vary across the Tetons. In the upper elevations of the central Tetons, the January 4th weak layer is likely buried by 3+ feet of hard, consolidated snow making it difficult, but not impossible for humans to impact said layer. This is not the case in other parts of the range. For example, the western slope of the Tetons and areas near Teton Pass have a thinner overlaying slab making human triggered avalanches more likely. While the likelihood of triggering an avalanche varies by location and elevation, the consequences of being caught in a large hard slab avalanche do not. Digging and probing for depths to the January 4th interface can provide useful information about the snowpack in terrain you wish to ride. However, it is safe to assume that poor structure exists across the zone and knowing exactly where a trigger point exists is very difficult. Warm temperatures and sun will add another layer of uncertainty to the decision making required in the backcountry today. Increasing your margin of safety to allow for surprises is a good idea given the current conditions. If you are uncertain about the likelihood of triggering an avalanche where you are riding, then defaulting to lower angle terrain that is not connected to overhead hazard remains the best option.

Régions couvertes