Bulletin d’avalanche

Togwotee Pass

Bridger-Teton Avalanche Center
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Danger d’avalanche

Fri
Alpin
3 · Marqué
Limite forestière
3 · Marqué
Sous la limite
Sans niveau
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Périmé — ce bulletin a expiré 4 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

Extreme winds and  8" of new snow in the past 36 hours created dangerous conditions that will require careful assessment and route-finding today.  The threat of natural avalanches, such as occurred yesterday in Hoback Canyon, has passed but widespread wind slabs combined with very weak snow beneath make large avalanches possible today.  Dig pits, observe snow surfaces for signs of wind loading and find your route cautiously if you brave the extreme cold to travel in the mountains today.

Problèmes avalancheux

  • Wind Slabs

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

    Due to the extreme winds, you'll find wind slabs up to a two feet thick in many areas with larger slabs in more exposed locations.  These may still be sensitive to triggering today. At upper elevations, slabs are more likely to be stubborn to triggering but will be much larger; two to three feet, maybe more in isolated areas. You'll find a mix of scoured terrain, sculpted snow surfaces, large drifts and cornices in most elevations and aspects today. Wind slabs also exist at lower elevations and though they are smaller, they are also more likely to be softer and still sensitive to triggering. By nature, the harder the slab, the more likely it is to crack a long distance from you rather than underfoot so check for hollow sounding snow and consider the extent of the wind slab above or beside you.  Look out for slabs that have developed lower on a slope and beneath cliff bands.

    (12/21/2022)

    We triggered two small slides on test slopes (N and SW aspects) on the Squaw Creek trail in the northern Greys forecast area. This is an example of the widespread nature of the wind slabs.

    Photo: Frank Carus

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    1.5–2.5

    Leeward areas may contain slabs 2-4' thick sitting on the weak layers of buried, faceted snow which have plagued our snowpack since late November.  The newly developed slabs may tip the balance towards instability.  Particularly troublesome slopes are those that have avalanched previously and reloaded (generally SE, E through N aspects),  solar aspects with a thin snowpack comprised of crusts and facets and steep rocky slopes like Angle Mountain. The Cow in the Woods slide yesterday morning in Hoback canyon is a good example of the very large avalanche that this layer could still produce. 

    (12/20/2022)

    SSE aspect at 9150 ft in Squaw Basin near the CD Trail. The pit revealed the loose sugary snow that has turned to facets. This process keeps snow grains from bonding together (sintering). The sqaures drawn on the snow indicate faceted snow.

Avalanche Discussion

Wind speeds on the summit of Rendezvous Peak yesterday morning hit 96 mph. Signs of extreme wind were everywhere with downed trees, sastrugi and debris scattered around even at valley locations. High snow desntities refleted the high wind as turbulence aloft began rounding snowfalkes before they even hit the ground.  Snow quickly formed slabs where none existed before with some natural avalanches observed even in the poor visibilty. Intentional human triggered avalanches were reported as well.  Signs of these wonds are numerous with fresh cornices that could fail under your weight and downed trees across trails.

Very cold temperatures are likely to sap these slabs of energy today and it seems likely that the number of human triggers in the mountains today will be small given the very cold temperatures. By the middle of the day, it is likely that conditions wil more accurately fit a the definition for moderate avalanche danger. The recency of the loading however, combined with the persistent slab problem creates the sort of conditions that will require very careful route-finding to figure out the intersection of these avalanche problems. 

Régions couvertes