Bulletin d’avalanche

Northwest Mountains

Crested Butte Avalanche Center
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Danger d’avalanche

Wed
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

Strong northerly winds drifted snow into sensitive slabs on leeward terrain features.  Skiers on Monday triggered a pair of avalanches on alpine terrain in the Ruby Range.  Visually inspect terrain to identify areas of wind-deposited snow and steer clear of those slopes.  Fresh drifts will likely feel stiff.  Sheltered terrain has been less problematic in the past few days, however, buried surface hoar in the upper snowpack could produce small slab avalanches in some places.  A quick dig into the snowpack will allow you to locate buried surface hoar in the upper snowpack.

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 and Monday, northerly winds increased to moderate speeds at ridgetops with strong gusts above treeline.  Strong winds persist on Tuesday with some continued loading possible.  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.  Fresh drifts will likely feel stiff or hard.  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 of specific features.

    12/25:  A pair of skier triggered wind slabs on the south side of Ruby Peak.  

    Photo: Zach Guy

  • 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

Storm totals from the weekend range from 2 to 10 inches across the forecast zones.  Strong northerly winds kicked up on Sunday night, blew through Monday, and were forecasted to continue on Tuesday.  There was plenty of blowing snow visible on Monday during daylight hours.  A handful of recent natural avalanches ran and skiers triggered a pair of avalanches on Ruby Peak on Monday.  You can typically identify areas of wind-deposited snow by reading the snow surface and surrounding terrain.  Avoiding leeward terrain features with evidence of drifting is a good idea for Tuesday.  Some Wind Slabs are fairly stiff and supportive to skis or board which may give a false sense of stability and lure you onto a slope before failing.  The likelihood of triggering a Wind Slab will taper off over the next few days but remain a concern on Tuesday.

You can find less avalanche danger at lower elevations in wind-sheltered areas.  There is a threat in some sheltered terrain to trigger a small slab avalanche on buried surface hoar in the upper snowpack.  On Sunday, observers found one of these areas on Mount Axtel.  Issues with surface hoar are more likely to be found in the Northwest Mountains due to deeper storm totals.  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 slab avalanche problem in sheltered areas.

Areas in the Southeast Mountains received less snow this weekend, around 2 to 5 inches.  You can expect to find sensitive Wind Slabs at upper elevations but drifts will be smaller and less commonly encountered.  Even though these avalanches are generally small, you don't want to risk injury taking a ride in an avalanche; there is also an outside chance that a Wind Slab could release a deeper avalanche as it runs downslope.  There could be some isolated features that have a large fetch adjacent where the wind could gather enough snow to produce a large 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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