Lawinenlagebericht

Northwest Mountains

Crested Butte Avalanche Center
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Lawinengefahr

Sat
Hochgebirge
2 · Mässig
Waldgrenze
2 · Mässig
Unterhalb
2 · Mässig
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Veraltet — dieser Lagebericht ist 6 years ago abgelaufen. Du siehst vergangene Verhältnisse, nicht den aktuellen Bericht.

Kernpunkte

The snowpack is on a slowly improving trend under a quiet weather pattern.  We are only a couple of days out from several large natural avalanches in the region, which highlight the ongoing potential for skiers or riders to trigger similar slides.   The most dangerous conditions are on leeward terrain features near and above treeline, where winds have formed larger and more cohesive slabs above weak snow. Today's avalanche problems can be remotely triggered and propagate wider than expected without giving clear warning signs.   Choose your terrain carefully.  

Lawinenprobleme

  • Persistent Slabs

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

    On or near steep terrain, you can trigger persistent slabs 2 to 4 feet thick that fail on weak snow near the ground.  Persistent slabs often surprise even the most experienced travelers: They give irregular feedback, they can propagate unusually wide distances, and they can be remotely triggered from below or adjacent to the slope.  To avoid this problem,  choose routes that stay off of, and out from underneath, steep terrain holding dense slabs over sugary weak layers.  Poor structure is most common on the slopes highlighted by the distribution rose above, on west to north to east and some southeast slopes.   Shooting cracks and collapses are clear warning signs to stay on slope angles less than about 30 degrees, although their absence isn't a guarantee of safety.   In the Northwest Mountains, slabs are generally thicker and denser: you are most likely to trigger them from shallow points on the slope such as rock bands, pungie trees, or where slabs taper in thickness from wind effects.  

    12/31: A large, remotely triggered persistent slab in Redwell Basin

Avalanche Discussion

Large grained weak layers near the ground have been on the losing side of a dramatic tug-of-war match against overlying slabs for most of December.  With quieter weather since January, the layers have started to adjust and gain traction against their opponent.  Clearly, it's still a close match: it only took a few inches of snow and wind transport on Tuesday to initiate more natural avalanche activity, including this impressive avalanche just north of our forecast area.  This is unnerving bullseye data that our buried weak layers aren't adjusting as quickly as we all wish they would.  Human triggering a similar avalanche is a distinct possibility on higher elevation,  leeward terrain.  Pay close attention to seasonal wind loading and scouring patterns if you are traveling in the alpine.   If there's a thick slab of drifted snow, you might be able to trigger it, especially from where the slab thins out near its margins.   

At lower elevations, the danger is improving quicker, especially in the shallower snowpack of the Southeast Mountains.  Dry weather this month is eroding and faceting away at slabs, giving the weak layers an upper hand in the tug-of-war match.  The number of concerning slopes is diminishing and the potential for wider propagation and larger slides is also trending down.  Even though we are seeing an improving trend, don't get complacent.   We are still receiving reports of obvious signs of instability in sheltered terrain, such as yesterday's observation of shooting cracks on Snodgrass.    Here is a recent video that demonstrates how the size and stiffness of slabs vary with elevation and from shallower to deeper snowpacks.  Unless the slab has lost all of its cohesion to a point where you are sinking through it on your skis or boards, treat it with suspicion.  

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