Bollettino valanghe

Southeast Mountains

Crested Butte Avalanche Center
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Pericolo valanghe

Wed
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
1 · Debole
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In sintesi

Strong winds and up to 4" on Sunday night formed small wind slabs scattered across higher elevation terrain, easily triggered by skiers yesterday.   Be cautious of lens-shaped, thicker-looking drifts if you are riding in high-consequence terrain above cliffs, gullies, or trees.  Although unlikely, there is lingering potential to trigger a high-consequence avalanche in terrain with shallow and variable snow depths.   Terrain with a snowpack deeper than 5 feet and sheltered from the wind offers the safest riding today.   

Problemi valanghivi

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–1.5

    A few inches of snow and gusty winds in the past 36 hours formed small drifts in wind-affected terrain.  Sunday night's winds were strong out of the southwest, and have since shifted to the north at lighter speeds. To identify the problem, look for signs of recent drifting, such as thicker or denser wind deposits and cracking underfoot.  Today's wind slabs are generally small and will be most harmful if they push you into a terrain trap.  They'll be most common near ridgelines and concave terrain features or rollovers that catch drifting snow.  

    2/6:  A skier triggered wind slab on a leeward slope on Mt. Emmons. 

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Unlikely
    Dimensione
    2–3

    In the Southeast Mountains, weak layers near the ground are buried 2 to 6 feet deep and have become a rare but consequential instability.  Slabs are most easily triggered where they are thinner.  Be cautious of wind-affected terrain with variable depths, rock bands, and snow-deprived areas 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), or on southerly aspects where recent warmups have strengthened the upper snowpack.

    2/1:  A large skier triggered persistent slab that failed on depth hoar at the ground near Park Cone.  

Avalanche Discussion

Today's avalanche danger is driven by the threat of small wind slabs across the entire forecast area at higher elevations, and low likelihood/high consequence persistent slab concerns in shallower parts of the Southeast Mountains.  The Sunday night through Monday morning storm brought 8" at Irwin and 3" at CBMR, with initially strong winds out of the southwest.  Skiers yesterday triggered small slabs in wind-affected terrain. It's worth highlighting that one of these was unintentionally triggered further down the slope than expected.  The wind slabs formed over a faceted snow surface, so they will probably remain sensitive to triggers today.  I expanded the distribution rose of wind slabs in the alpine after last night's gusts out of the northwest to the northeast may have formed fresh drifts on the opposite side of the compass.  This problem is generally small, but something you'll want to manage in high-consequence, wind-affected terrain.  

We're shifting the upper snowpack persistent slab (our mid-January near surface facet layer) from stubborn to unreactive in our assessments.  Dozens of aggressive tracks in suspect terrain over the weekend and recent targeted stability tests (Ex A, Ex B) provide evidence of the upper snowpack persistent slab problem becoming increasingly rare, so we've removed it from our problem list.  In contrast, persistent slabs breaking on basal weak layers are still a concern in the Southeast Mountains because those depth hoar layers are much larger and better developed, thus slower to improve.  Evidence of the lingering problem comes from a close call last Wednesday, just outside of our forecast area on Park Cone, and unstable pit results over the weekend on a shallow, windward slope near treeline by Gothic.  

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