Lawinenlagebericht

Southeast Mountains

Crested Butte Avalanche Center
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Lawinengefahr

Tue
Hochgebirge
2 · Mässig
Waldgrenze
2 · Mässig
Unterhalb
2 · Mässig
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Veraltet — dieser Lagebericht ist 5 years ago abgelaufen. Du siehst vergangene Verhältnisse, nicht den aktuellen Bericht.

Kernpunkte

Skiers and riders have the potential to trigger very large and destructive avalanches today.  Slopes that face the northern half of the compass and have a shallow snowpack are most suspect.  Safer riding is on wind-sheltered southerly aspects, or where the snow coverage is deep and uniform.  

Lawinenprobleme

  • Persistent Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    2–3.5

    It is possible to trigger a very large and destructive avalanche today in steep terrain or from flatter terrain where the snowpack connects to a start zone.  These widely propagating and long-running avalanches will break 3 to 5 feet thick or more on weak layers near the bottom of the snowpack.    Persistent slabs are most likely to be trigged on the northern half of the compass, where buried layers are most fragile.  Slabs have grown stubborn to human triggers because of how thick they are.  You are most likely to trigger a persistent slab avalanche where slabs are thinner.  Thin areas are more common in terrain that has seen less snow, or at higher elevations where the wind has redistributed snow into variable snow depths.      

    A recent persistent slab avalanche that broke wide and deep on weak layers near the ground.  

  • Wind Slabs

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

    Northerly winds on Saturday formed drifts in leeward terrain on the southeastern quadrant of the compass near and above treeline.  These drifts are getting more difficult to trigger, but they could be stiff enough to break above you.  Today, alpine winds are increasing out of the southwest, and could be forming small, sensitive drifts on the northeast quadrant of the compass at the highest elevations.   Look for thicker, denser lobes of drifted snow or blowing snoww to identify the problem.  They'll be most common below alpine ridgelines or in crossloaded terrain features.

    A small wind slab that ran naturally on the south face of Mt. Owen sometime around 1/2.

Avalanche Discussion

Yesterday, our staff took advantage of the clear skies to document extensive carnage from the last cycle.  We'll be entering the slide info into our database over the next couple of days, but for now, this observation summarizes the activity and you can view the photos here.  Apart from the extensive persistent slab activity that ran on 12/31, we also noted a handful of small wind slabs that released naturally early yesterday or the night prior, and a few destructive persistent slabs that ran sometime around 1/1 or later that night from wind loading. 

The snowpack continues to consolidate and adjust from the major loading event that brought over 14" of SWE to Schofield Pass and over 7" of SWE to Upper Taylor.   We've made a few tweaks to the problems now that our data gaps are filling in.  In the Northwest Mountains, we have shifted the problem to a deep persistent slab problem.  Deep slabs are characterized by low likelihood, very high consequence setups.  In the Northwest Mountains, the likelihood of triggering an avalanche that fails on deeply buried weak layers has decreased to unlikely given how thick and dense slabs are.  In isolated terrain features, you may be able to still bring the walls down.  That could be from a shallow, rocky area or on the margin of a slab where winds have thinned the snowpack.    In the Southeast Mountains, the slabs are a bit thinner and the likelihood of triggering is higher.  Slabs will be most reactive in shallow areas (see this observation).  In both regions, our travel advice is to go towards deeper, more uniform snowpacks. 

The other change is that we have trimmed southerly aspects from the distribution rose to highlight that triggering a persistent slab on these aspects is far less likely.  Our evidence for such is three-fold:  1) Our pre-storm observations highlighted that the 12/23 facets were small grained (less than 1mm) on these aspects, thus less likely to persist for long periods of time.  2)  Targeted observations during and after the loading event suggest that propagation potential has diminished on these aspects due to weak layers on these aspects rounding and strengthening  3) Our assessment of avalanche activity during the cycle showed relatively minimal avalanche activity on southerly aspects, in stark contrast to the rest of the compass.   This video that we put together during the last few field days demonstrates some of the aspect differences. 

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