Lawinenlagebericht

Southeast Mountains

Crested Butte Avalanche Center
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Lawinengefahr

Mon
Hochgebirge
3 · Erheblich
Waldgrenze
3 · Erheblich
Unterhalb
3 · Erheblich
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Kernpunkte

More snow and an increase in winds overnight keep the snowpack under distress. Numerous large natural avalanches released in the last few days from increased winds, and collapsing snowpacks have been relentless at lower elevations.  Slabs are often an ideal depth for human triggering, and remain sensitive where they formed over the shallow and weak snowpacks left behind in steep terrain by the Thanksgiving cycle.  Last week featured numerous close calls in the Elk Mountains (see our weekly summary).   Conservative terrain choices on west, north, east, and high elevation south aspects are essential.  The safest riding is on slope angles under 30 degrees or wind protected southerly slopes at lower elevations.  

Lawinenprobleme

  • Persistent Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Likely
    Größe
    1.5–2.5

    Slabs averaging 1 to 2 feet thick in sheltered terrain and larger in wind-loaded terrain are most sensitive where they formed over well-developed facets and collapsible crusts on west, north, and east aspects. Additionally, wind-loaded slabs can fail above the stout crusts on high elevation, southerly aspects. Slab behavior is challenging with variable and deceptive feedback, remote triggering potential, and wide propagation across terrain features.  You may not see obvious warning signs, such as collapses or cracking, before triggering an avalanche. You can reliably avoid the problem on slope angles less than 30 degrees without steeper slopes above you.  You can significantly reduce your risk on lower elevation southerly aspects.    

  • Wind Slabs

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

    Moderate to strong northerly winds drifted up to 6" of new snow over the 24 hours.  Watch for shallow soft slabs breaking below leeward ridgelines, rollovers, or crossloaded gullies at higher elevations.  Look for deeper, denser drifts or cracking in wind loaded terrain to identify the problem.  These slabs will be most dangerous in high consequence terrain or if they step down and trigger a larger persistent slab described above.  

    A thin slab triggered yesterday on Mt. Emmons.  Watch out for soft slabs like these in wind loaded terrain features today.  

Avalanche Discussion

Storm totals range from 4" at CBMR to 10" in the Slate and 18" around Kebler Pass.   In areas where the storm over-delivered, observers reported sensitive sluffs, wind slabs, and storm slabs up to D1.5 in size (ex. Anthracites, Irwin).   Elsewhere, the new snow is only a problem where northwest to north winds are drifting it into more cohesive slabs.  Storm slab instabilities in low-density snow are typically short-lived after the loading period ends, but could remain sensitive today, especially at higher elevations where winds have stiffened the new snow.  Issues in the storm snow will be easy to recognize: look for cracking, use small test slopes, and know that a storm instability can gain enough mass to step down in terrain where persistent slabs are highlighted. 

The larger and more difficult problem to manage is slabs breaking on our weak layers deeper in the snowpack, which now range from about 4 feet deep around Kebler Pass to a foot deep in the shallowest parts of our forecast area near town.  In the Southeast Mountains and terrain near the boundary of the two zones, we continue to find evidence that the problem is reactive and easy to trigger, with abundant recent naturals and consistent reports of collapsing.  In much of the Northwest Mountains, the likelihood of the problem appears to be gradually decreasing (see this observation from the Slate).  It's important to recognize that the drop from "likely" to "possible" was not a dramatic and sudden change, but rather a gradual transition on a sliding scale:  "Possiblikely".   The seriousness of triggering a persistent remains the same: slabs will be large enough to injure or kill you in all but small terrain features.  

Events:  Our next Fireside Chat is this Thursday, 7 p.m., at the billy barr lounge, where Danielle Beamer will discuss Mental Health and Backcountry Decisions.  The event is free and open to all.  

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