Bulletin d’avalanche

Southeast Mountains

Crested Butte Avalanche Center
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Danger d’avalanche

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

Points saillants

Wind-sheltered terrain with a deep and uniform snowpack offers the safest riding today.  Sensitive wind slabs have formed a relatively small hazard in leeward terrain at higher elevations, exemplified by several skier-triggered slides yesterday (Ruby, Schuylkill).  In the Southeast Mountains,  triggering a large and dangerous persistent slab remains possible.  Be cautious in snow-deprived areas where slabs are only a few feet thick or in wind-affected terrain where slopes with a thin and variable snowpack are more common. 

Problèmes avalancheux

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    2–3

    In the Southeast Mountains, faceted weak layers are buried 2 to 6 feet deep and are becoming more difficult to trigger as layers adjust to the last month of active loading.  Slabs are most easily triggered where they are thinner, which is most common in shallow areas near Crested Butte and CB South, or in wind-affected terrain.   Be cautious of windward terrain features with variable depths, rock bands, and slopes where slabs are only a few feet thick.   The safest riding is where the snowpack is uniform and consistently deeper than about 5 feet (150 cm).  

     

    This large persistent avalanche was explosively triggered on Mt. Crested Butte on 1/17.  It exemplifies the destructive size, and one example of the type of terrain that is troublesome.

  • Wind Slabs

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

    Observers yesterday triggered a handful of fresh wind slabs 6" to 12" thick.  Northwest winds are forecasted to increase later today, which will thicken yesterday's slabs or form a fresh batch.  Wind drifts are most common below ridges, in crossloaded gullies, and below abrupt rollovers.  Be especially cautious in large or consequential terrain.  Cracking snow and blowing snow are signs of instability.  Most slabs are expected to be small, although there could be isolated exceptions in terrain with large fetches.  

    1/24: A skier triggered wind slab that broke about a foot thick on Ruby Peak.  

Avalanche Discussion

We are keeping the danger elevated in the Northwest Mountains today because yesterday's observations suggest that wind slab formation was a bit more widespread and reactive than anticipated.  Winds are expected to increase again later today, which will continue to fuel the problem.  Some drifts will be stubborn today, while others are forming over a reactive weak layer of near-surface facets that formed during our recent dry weather.  You'll need to manage this problem using visual clues and feeling for thicker drifts if you are riding in large or consequential wind-exposed terrain.  

The relatively quiet weather of the past week has given weak layers near the ground a chance to recover and adjust to the month-long loading period.  Our forecast team has been discussing whether we can phase the persistent slab problem off the list in the Northwest Mountains.  Our pit work yesterday on Ruby Peak suggested layers are becoming unreactive, while explosive work at Irwin yesterday produced some deep cracking and a large collapse with a hand shot.  That suggests that we aren't quite out of the woods yet in the deep zone:  there still may be a few slopes out there that could bring down the house if you hit a shallow trigger point.  The easiest solution to safeguard against that very low likelihood but high consequence threat is to ride where the snowpack is deep and uniform.  In parts of the Southeast Mountains, it's an unhappier story, where the snowpack has remained thinner and weaker this season.    For example, stability tests near Red Mountain on Tuesday produced unstable results on both of our prominent weak layers in the lower snowpack, both at ideal depths for human triggering.   Although there's a lot of variability across the Southeast Mountains right now, stability involving deep layers is generally improving.  You'll want to assess each slope on a case-by-case basis.  This map of modeled snow depths around our forecast area paints a generalized picture of the deeper and more trustworthy areas vs. the have-nots.  The goldilocks snow depth for finding the most troublesome structure seems to be around 3 to 4 feet (90 to 120 cm).  

Régions couvertes