Lawinenlagebericht

Northwest Mountains

Crested Butte Avalanche Center
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Lawinengefahr

Sat
Hochgebirge
3 · Erheblich
Waldgrenze
3 · Erheblich
Unterhalb
3 · Erheblich
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Kernpunkte

Dangerous avalanche conditions persist.  A recent storm deposited 2 to 3 feet of storm snow above well-developed weak layers which produced an impressive natural avalanche cycle over the past several days.  Human triggered avalanches remain likely and natural avalanches remain possible on slopes that endure continued wind-loading.  The most effective strategy for managing today's avalanche conditions is to choose slopes 30 degrees or less in steepness.  Give steep terrain a wide berth to prevent triggering an avalanche from below or adjacent terrain.

Lawinenprobleme

  • Persistent Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Likely
    Größe
    1.5–3

    Natural and human-triggered slabs breaking several feet thick are very likely today.  2 to 3 feet of new snow and strong winds have formed touchy slabs on top of exceptionally fragile facets and faceted crusts.  The avalanches can be triggered from below steep slopes, they can propagate surprisingly wide distances, and they can fail spontaneously on slopes with continued wind-loading.  Expect this problem to remain sensitive to human triggers for days to come.  The observations page and avalanche table are brimming with evidence of the widespread natural cycle that lasted for several days this week.   Choose slopes that are consistently less than about 30 degrees that don't connect to steeper terrain above you.  

    This slab failed on a collapsible crust and propagated 1500 feet wide.  

  • Storm Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    1–2

    With light snowfall and continued wind-loading today, avalanches breaking on layers within the storm snow is a potential threat.  In most terrain, slabs breaking within the storm snow will immediately step down to release a persistent slab that fails on the dry spell weak layer a few feet down.  On south to southwest aspects, the step-down and unusual slab behavior is less likely, so you'll be managing for storm slabs running on crusts or on layers within the storm snow.   Cracking and signs of recent drifting are red flags for this problem.

    A Storm Slab avalanche failed naturally sometime Thursday morning in the Anthracite Range.  All of the recent storm snow, about 2 feet deep, ran above the old melt/freeze crust on a southerly aspect.

Avalanche Discussion

A few inches of snow fell overnight and southwest to west winds increased allowing for more wind-loading on leeward features.  Continued wind-loading will maintain the threat of natural avalanches.  Dangerous avalanche conditions exist due to the likely chance of human-triggered avalanches and the possibility of large natural avalanches where the wind transports snow.  You can read through these two observations with reports of fresh natural avalanches from yesterday on drifted terrain (observation 1, observation 2).

On slopes that face west through north through southeast at all elevations, the hazard is well defined and understood.  Slabs from the recent storm are resting above horrendous persistent weak layers and most steep slopes are primed and ready, just waiting for a trigger like you to come along and release a dangerous avalanche.  Take a look at our observation page to see the mountain of evidence demonstrating the dangerous conditions on these aspects.  This is why the travel advice is simple avoidance.  Choose lower angled slopes that are not connected to or underneath steeper terrain. 

A change was made to the Storm Slab avalanche problem today.  We removed it from below treeline elevations.  Most below treeline slopes are covered by the Persistent Slab avalanche problem which leaves south and southwest slopes below treeline NOT covered by a problem.  Near and above treeline south and southwest slopes remain suspect and untrustworthy due to wind-drifting in the storm snow.  To be clear, this is not a green light to run wild on south and southwest slopes below treeline.  Rather the evidence, like natural avalanches, snowpack tests, and field observations, suggest that these slopes are not the most likely place to trigger an avalanche, yet still possible.  South and southwest slopes below treeline have a 2 to 3-foot slab resting over a melt/freeze crust that in some places may produce an avalanche.

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