Lawinenlagebericht

Southeast Mountains

Crested Butte Avalanche Center
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Lawinengefahr

Fri
Hochgebirge
2 · Mässig
Waldgrenze
2 · Mässig
Unterhalb
1 · Gering
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Veraltet — dieser Lagebericht ist last year abgelaufen. Du siehst vergangene Verhältnisse, nicht den aktuellen Bericht.

Kernpunkte

You can trigger relatively thin avalanches of drifted snow, most commonly on leeward slopes near and above treeline.  Numerous human-triggered slides yesterday exemplify the problem. Wind-sheltered terrain offers safer travel.  On high, northerly aspects, there's a small chance you can trigger a much larger slab in steep terrain where snow depths are thin and variable.

Lawinenprobleme

  • Wind Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    1–1.5

    This week's new and windblown snow has formed wind slabs on leeward terrain features favored by westerly winds. Winds are shifting to the southeast and south today, potentially forming a new generation of wind slabs on north to west aspects.  These slabs formed over various surfaces, including slower-to-heal facets on some slopes.  Carefully assess slab size and terrain consequences before riding in steep, leeward terrain.  Fresh wind slabs are commonly found below corniced ridgelines, abrupt rollovers, or in crossloaded gullies.  Cracking, collapsing, and thick/stiff drifts indicate the problem.  You can avoid the problem on wind-eroded or wind-sheltered terrain.   

    Examples of several small wind slabs that ran naturally during Tuesday's storm. 

  • Persistent Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    2–2.5

    The snowpack remains winter-like on high, northerly aspects, and faceted weak layers linger near the bottom of the snowpack.   Persistent and deep persistent slabs are most likely triggered by cornice falls, or there's a slight chance you can trigger one from a shallow or rocky part of a steep slope.   Terrain where the snowpack is unusually shallow from wind effects or previous avalanche activity is most concerning.  You can reduce your risk by traveling where the snowpack is deep and uniform, and you can avoid the problem on sunnier aspects that have a spring-like snowpack that saw extensive meltwater last week.

    A recent persistent slab above Peeler Lakes. This is a great example of the most worrisome terrain: thin, rocky, and wind-affected.   

Avalanche Discussion

Clearing skies yesterday allowed us to extract some avalanche patterns from Tuesday's storm, which produced up to 20" in the Northwest Mountains and less than 6" in the Southeast Mountains.  Storm instabilities were most active near and above treeline and favored the Northwest Mountains.   A handful of these avalanches were large enough to bury you (D2 in size), and these generally occurred on large, leeward slopes near alpine summits.  Although most storm instabilities are improving, some formed over faceted weak layers and are slower to heal.   These forecaster observations from Baxter Basin and Elkton discuss the spotty distribution and inconsistent pattern of this buried weak layer, which was likely the cause of the remote trigger in Marble yesterday.  We're still calling the problem a storm slab today, but the problem is expected to transition into a new generation of persistent slabs as time goes on. Choosing terrain with smaller consequences can help you manage uncertainty where recent storm totals exceed a foot or more.   The problem is easier to navigate in the Southeast Mountains because slabs are generally smaller and only formed on wind-loaded terrain features.  Another round of fresh wind slabs could form from today's snow and southerly winds. Below treeline, slab instabilities are generally small and isolated, and the avalanche danger is Low this morning.  We're showing Moderate danger in the Northwest Mountains below treeline due to uncertainty with incoming storm totals today; if we reach or exceed the high end of snow forecasts, storm instabilities could become more active.   

A notable exception to the pattern of storm instabilities is this large natural avalanche above Peeler Lakes.  This appears to be a recent hard slab that failed on old weak layers. High northerlies are the only slopes that didn't see extensive meltwater into the snowpack last week. On those colder aspects, a more winter-like snowpack structure exists and requires consideration for the early-season weak layers that have plagued us this winter, especially on terrain with unusually shallow snow depths. The most recent human-triggered examples of the problem include a snowmobile-triggered slide on Axtell and a skier-triggered slide on Gothic.   In the San Juans yesterday, a skier was surprised when they triggered a shallow wind slab that stepped down and produced a very large avalanche. 

Events: CBAC's Party for the People is at the Talk of the Town next Thursday.  Come celebrate the end of the season with us!  (Don't worry, we'll be forecasting for at least a few more weeks.)

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