Avalanche forecast

Northwest Mountains

Crested Butte Avalanche Center
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Avalanche danger

Mon
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
2 · Moderate
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Highlights

Yesterday's storm delivered 6 to 12 inches with areas west and north of town accumulating the most.  Strong westerly winds transported snow onto easterly aspects at upper elevations.  Cracking in drifted snow is a sign you have found unstable conditions.  Beneath the recent storm snow is thick slabs that formed during the holidays which rest upon weak layers near the ground particularly on the north half of the compass.  Triggering an avalanche that breaks deeply is a lower likelihood but high consequence event.  Slopes with variable snow depth and terrain that avalanched earlier in the winter increase your chances of triggering a broad and deep avalanche.  Sheltered terrain and south-facing slopes offer relatively safer conditions.

Avalanche problems

  • Deep Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2.5–3.5

    The snowpack structure for this avalanche problem is the most widespread on the northern half of the compass, where buried layers are the most fragile. Slabs have grown stubborn to human triggers because of how thick they are. You are most likely to trigger a monster avalanche where slabs are thinner. Thin areas are more common at higher elevations where the wind has redistributed snow into variable snow depths, and where the snowpack thins near rock outcrops. These widely propagating and long-running avalanches would break 6 to 10 feet thick or more on weak layers near the bottom of the snowpack.  

    A deep persistent slab avalanche near Yule Pass that released around 12/31.  

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–2

    Moderate to strong westerly winds will drift the new storm snow into shallow slabs on leeward aspects and cross-load windward features.  Reports of small Surface Hoar formation on some shaded near treeline terrain may make Wind Slabs more reactive.  Wind Slabs will be most commonly found beneath ridgetops, underneath corniced features, and cross-loaded in windward gullies.  Active snow transport will provide clues on distribution if visibility allows.  Cracking on small, drifted features is good evidence of a sensitive Wind Slab problem.

    A Wind Slab avalanche was observed last week below an alpine ridgeline.  You can expect similar slab formation today at upper elevations.

Avalanche Discussion

Areas to the west and north of town received up to 12 inches of new snow accompanied by strong westerly winds.  Anticipate finding freshly formed slabs at the surface on leeward terrain features at upper elevations.  Winds dropped to low speeds yesterday afternoon and the drifting likely stopped then.  If you are venturing into alpine areas take the time to identify drifted features and assess conditions before you commit to leeward terrain.  Observing recent natural Wind Slabs or cracking in small test features is a good sign that you have found sensitive avalanche conditions.  Expect the Wind Slab problem to have a greater distribution and increased size for areas in the Northwest Mountains where more snow accumulated yesterday. 

The Deep/Persistent Slab problem continues to require your attention.  The likelihood of you triggering a very large avalanche that fails near the ground is decreasing, but cannot be ruled out.  Slopes with uniform depth, greater than about 6 feet, will help reduce the risk of you finding a trigger point like a thin part of the slab near rocks or cliffs.  Slopes with uniform depths are more common below treeline where winds haven't been able to redistribute snow.  Southerly-facing terrain offers less risk because basal weak layers are far less common.  It's a sure bet that northerly-facing terrain possesses weak snow at the ground.  Watch this video by Zach Guy for more information on the Deep Persistent Slab problem (also viewable in the gallery below).  Additionally, there is a concern for slopes that avalanched earlier this winter and subsequently redeveloped a slab.  This observation from Climax Chutes illustrates that some slopes with previous avalanche activity have maintained basal weak layers and rebuilt thinner slabs above that may be more prone to human-triggering.  With a bit of detective work, you can identify a good number of these slopes with previous avalanche activity by looking through our Observations Page and inspecting the Avalanche Table.

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