Lawinenlagebericht

Northwest Mountains

Crested Butte Avalanche Center
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Lawinengefahr

Fri
Hochgebirge
4 · Gross
Waldgrenze
4 · Gross
Unterhalb
4 · Gross
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Kernpunkte

Avalanche conditions are very dangerous.  Snowfall yesterday and last night are overloading the snowpack.  You are very likely to trigger an avalanche in the upper snowpack on many slopes, and some locations can fail deeper in the snowpack producing a widely propagating avalanche that runs far.  You can trigger avalanches from below or adjacent lower-angled terrain and some could release naturally.  Travel in or below avalanche terrain is not recommended today.

Lawinenprobleme

  • Persistent Slabs

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

    Many slopes have weak snow at the bottom of the snowpack, and new slabs have formed over persistent weak layers in the upper snowpack which are reactive to the weight of a human. A triggered avalanche in the upper snowpack could step down to deeper weak layers near the ground, becoming much larger than expected, and producing a destructive avalanche. This avalanche problem can propagate widely through the terrain, or be remotely triggered from low-angle slopes connected to steeper slopes.

    Avalanches could step down into deeper weak layers such as this human-triggered avalanche on 12/27.

  • Storm Slabs

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

    Recent warm temperatures combined with the recent storm snow created widespread surface slabs. Avalanches averaging 8 to 18 inches thick will be likely to human trigger on many slopes near or above 35 degrees in steepness. Careful snowpack evaluation and cautious route finding will be essential when traveling near avalanche terrain.  Aspects and elevations where the Storm Slab problem overlaps with the Persistent Slab problem could result in a surface avalanche 'stepping down' to deeper weak layers.

    Shooting cracks or a collapsing snowpack are obvious red flags that the snowpack is unstable. 

Avalanche Discussion

The recent storm produced totals ranging from about 7 to 18+ inches of dense, heavy snow with areas in the Northwest Mountains being the clear winners.  Locations where you find more than a foot of snow are the most dangerous as avalanches will commonly be big enough to bury and kill you.  Travel in or below avalanche terrain is not recommended for areas in the Northwest Mountains.

Peak instability and much of the natural avalanche activity likely occurred last night and during the early morning hours as the final strong pulse of moisture pushed through while we all slept.  However light snowfall continues in the Northwest Mountains this morning and continues to stress the snowpack which will keep the threat of natural avalanches going.  You can expect very easy-to-trigger avalanches in the Northwest Mountains on most steep slopes that did not run naturally.  This observation from the Anthracites points to widespread weak layers nearing their tipping point yesterday afternoon and with additional snowfall last night and this morning conditions have worsened due to thicker slabs and an increased threat of natural avalanches.   Thoughtfully avoid traveling on or underneath avalanche terrain as some avalanches may run further than expected.

The terrain in the Southeast Mountains remains dangerous but slightly less so than in the Northwest Mountains.  The same weak layers exist (surface hoar, near-surface facets, and basal depth hoar) but overlying slabs are smaller due to less snowfall.  Observers reported triggering avalanches yesterday during the first half of the storm on Snodgrass and few more inches of snowfall overnight are keeping the pressure on the snowpack.  Avalanches are expected to be smaller in the Southeast Mountains, with many small avalanches and some large avalanches.  Make no mistake you can be buried, injured, or killed today by an avalanche in the Southeast Mountains just in fewer locations.  

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