Bulletin d’avalanche

Northwest Mountains

Crested Butte Avalanche Center
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Danger d’avalanche

Tue
Alpin
3 · Marqué
Limite forestière
2 · Modéré
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

An increase in northerly winds and low-density storm snow create dangerous conditions on leeward terrain features at upper elevations.  Human-triggered avalanches are likely in wind-drifted storm snow.  There is a small chance for an avalanche in the storm snow to release a larger avalanche as it runs down the slope.  In steep wind-protected terrain, you can trigger loose avalanches, and possibly a thin slab, in the recent snow.   You can enjoy this cold and sunny Christmas by avoiding wind-drifted slopes and favoring southerly-facing, low-elevation terrain options.  

Problèmes avalancheux

  • Wind Slabs

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

    Up to 10 inches of new snow fell this weekend with generally light to moderate winds.  On Sunday night, northerly winds increased to moderate speeds with strong gusts above treeline.  Expect to find sensitive avalanche conditions where the northerly winds drift the new snow.  Some avalanches could grow large enough to bury or injure you.  Read the snow surface to identify areas below ridge tops or cross-loaded behind ribs where the wind deposited snow.  The most likely place to encounter a Wind Slab is on the south half of the compass, and possibly on more northerly slopes depending on local loading patterns.  Slopes that have a large fetch are the most concerning for a large Wind Slab.

    A couple of natural avalanches from Sunday along the leeward east side of Purple Ridge.  Expect similar conditions on Christmas but the size of avalanches may have increased due to stronger winds last night.

    Photo: Eric Murrow

  • Storm Slabs

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

    Storm totals range from 5 to 10 inches in the Northwest Mountains.  Small soft slabs will be possible to trigger where they have formed over weak snow. Those near-surface facets and surface hoar weak layers primarily existed on the northern half of the compass.  There is a remote possibility that an avalanche triggered in the new snow, could further step down into the persistent slab avalanche problem or simply entrain weak snow as it runs down slope and grows larger than expected. 

    A small soft slab that was triggered on Saturday 12/23. 

  • Persistent Slabs

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

    Slabs 1 to 3 feet thick exist over several persistent weak layers in the snowpack:  Weak facets and depth hoar near the ground and surface hoar layers in the upper snowpack. The problem was most common on northerly and easterly facing slopes earlier this month, along with some wind-loaded westerly facing terrain. After below-average snowfall for the last two weeks, these weak layers are expected to be temporarily dormant on most slopes, with the potential for isolated exceptions from the small amount of loading this weekend. The most suspect areas could be, extreme terrain, unsupported slopes, or previously wind-loaded terrain features. You can reduce your risk by traveling on south-facing slopes that have thick crusts, or by traveling on smaller terrain features without terrain traps.  You can avoid the problem on slopes consistently less than 30 degrees. 

    This large persistent slab was triggered by skiers descending the ridgeline on the Aspen side of the Elk Mountains last weekend, 12/17.  

Avalanche Discussion

Merry Christmas and Happy Holidays!

Storm totals range from 2 to 10 inches across the forecast zones.  The most snow fell in the Northwest Mountains along the Ruby Range and thus the greatest avalanche hazard can be found in the Northwest Mountains on slopes drifted by northerly winds.  Conditions above treeline are flirting with dangerous where you find wind-deposited snow.  An observation from Purple Ridge on Sunday gives a little taste of what you can expect on Christmas; Wind Slabs likely grew larger on Sunday night and increased in distribution.  Some drifted slopes in the Northwest Mountains may be able to produce a large avalanche in the storm snow alone.  Your best and safest strategy is to avoid upper-elevation terrain where you find evidence of fresh drifting.

You can find less avalanche danger at lower elevations in wind-sheltered terrain.  Observations from Sunday reported sloughing, or Dry Loose avalanches, as the primary concern.  One observer on Axtel was able to find buried Surface Hoar in the upper snowpack that produced signs of instability and small slab avalanches.  You can dig into the upper snowpack to look for buried Surface Hoar before committing to steep, sheltered terrain on the north half of the compass.  Sunny slopes at lower elevations lack the facets and Surface Hoar driving the storm slab avalanche problem.

Areas in the Southeast Mountains received much less snow and therefore the avalanche danger rating is lower.  You can expect to find sensitive Wind Slabs at upper elevations but at a smaller size.  Even though these avalanches are smaller, you wouldn't want to ruin your Christmas by taking a ride in an avalanche.  Sheltered terrain in the Southeast Mountains has generally safe conditions.  Not enough storm snow accumulated to cause many problems outside of small loose avalanches on very steep slopes.  

 

Avalanche Beacon Park Update:

Want to practice your avalanche beacon skills over the holidays? A practice area is currently set up behind the community school (located here). The control box that runs the normal park is out for repairs, but in the meantime, there are two beacons buried in the training park. Get out there and get some practice over the holiday!

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