Bulletin d’avalanche

Tetons

Bridger-Teton Avalanche Center
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Danger d’avalanche

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

Points saillants

The chance continues for backcountry riders and skiers to trigger slab avalanches involving buried weak snow layers at the mid and upper elevations. Although these slabs have become less sensitive, the weak layers are well preserved.  Careful snowpack evaluation or staying on lower angle slopes are the best methods to safely travel through avalanche terrain at this time. Lower elevations lack enough snow coverage for significant avalanche concerns. 

Problèmes avalancheux

  • Persistent Slabs

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

    Weak snow that formed during a dry period in November remains a real concern on W-N-E aspects above 8000'.  Time and above average temperatures have decreased the sensitivity of these slabs which makes their failure harder to predict as it could occur when the first person impacts the terrain or after it has been tracked several times and a weak spot is crossed.  If triggered, these slabs are likely to be hard with crown depths of 2-3 feet. Avoiding being in or under steep terrain on these aspects. 

     

    (12/12/2023) A recent avalanche showing a crown depth taper from shallower new snow to a large, 3-foot-deep avalanche.

Avalanche Discussion

The decrease in the danger rating to Moderate is often interpreted as a green light to hit more aggressive terrain. It is not, especially in cases where a persistent weak layer is involved. As the existing slabs progress more and more from being “sensitive” to being “stubborn” it makes their release much more difficult to predict as it can occur after a slope has been tracked. When persistent slab problems evolve to this stage, vigilance to sticking with conservative terrain and thoughtfulness about the snowpack in the specific terrain is still warranted.

There is a lot of snowpack information currently available. Reading the posted observations shows that the PWL (persistent weak layer) has a lot of variability with some areas having simply a thick faceted snow layer and others have a mix of facets (including surface-hoar), melt-freeze, and rain-crusts. All of these fall into the PWL classification and have been in active during the December storm cycles. 

The current dry period is providing for future concerns with south facing slopes forming melt-freeze crusts while surface facets are developing in colder shaded terrain.

Régions couvertes