Lawinenlagebericht

Southeast Mountains

Crested Butte Avalanche Center
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Lawinengefahr

Fri
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

Mother nature deposited 2 to 5 inches in the Southeast Mountains accompanied by gusty southwest winds.  Expect to find sensitive shallow drifts on leeward terrain features and an increase in available snow for loose avalanches to accumulate as they run.  Old, hard slabs remain scattered on leeward terrain features that are now buried by storm snow which makes visual identification difficult.  Use increased caution on drifted terrain to prevent triggering a slab that could step down into the older, hard slabs and be prepared to effectively manage loose snow avalanches on sheltered northerly terrain.

Lawinenprobleme

  • Wind Slabs

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

    Southwest winds transported the new snow to leeward terrain features and formed fresh, shallow slabs.  You are likely to find Wind Slabs beneath ridgetops, below cornices, and cross-loaded on gully features.  Active transport, cracking, or cohesive surface snow and signs that you have found fresh drifts.  A triggered Wind Slab could entrain old, weak snow as it runs increasing the volume of debris.

    A wind-drifted slab from earlier this winter tucked beneath a ridgetop.

  • Persistent Slabs

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

    Strong northwesterly winds last week raked the mountains and mixed into typically more sheltered locations.  The incremental wind drifting built hard slabs ranging from just a few inches to several feet thick that is now buried and obscured by recent storm snow.  Although you can find these slabs at any elevation, we've seen the most significant wind loading and slab formation occurring nearing treeline, especially in terrain with large fetches favored by northwest winds.   These slabs are slower to heal because they formed above exceptionally weak facet layers.  They can also be remotely triggered from below or adjacent to steep slopes where the drifted snow spans onto lower slope angles.   The problem is localized to leeward terrain features behind tree fences, on the lee sides of ridged terrain features, and in concave catchments such as gullies.   Collapses and shooting cracks are clear warning signs of the problem.  Give wind-loaded terrain a wider berth than normal as surface clues have been buried by the recent storm snow: there have been several near misses this week with some slides breaking into lower-than-usual slope angles.

  • Loose Dry

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

    Dry loose avalanches (sluffs) are a concern in wind-sheltered terrain on the north half of the compass.  Where the snow surface is weak and cohesionless, you can easily trigger sluffs that entrain the top 8" to 14" of loose snow on slopes steeper than 35 degrees.  The recent storm has increased the snow available for loose avalanches to entreain.  Ski cuts, moving across the fall-line while descending, or choosing lower-angled slopes are effective techniques to manage this problem. These point-release avalanches will accumulate more mass in long-running, steep terrain. Use caution above gullies where an avalanche can pile more deeply and above trees and cliffs where the consequences of getting caught in a sluff will be magnified. This problem is most common in sheltered terrain below treeline, but you can also trigger sluffs on some near treeline slopes and a few above treeline slopes.    

Avalanche Discussion

Wednesday's storm delivered 2 to 9 inches of snow.  The Northwest Mountains accumulated 4 to 9 inches with the highest totals in the Ruby Range.  The Southeast Mountains picked up 2 to 5 inches of storm snow.  This difference in snow totals is the key point in the diverging danger rating between the two zones.  There is a variety of avalanche problems to manage today depending on aspect, elevation, and location in the CBAC forecast zone.  What follows will help you make sense of the variety of surface instabilities you may encounter today.

Wind Drifted Terrain:  Leeward terrain features will have formed fresh slabs at upper elevations from southwest winds that will be sensitive to the weight of a person.  Fresh wind-drifted slabs will be the biggest and most concerning for areas that accumulated the most storm snow.  Finding more than about 7 inches of drifted snow is a good clue that you have found increased avalanche hazard.  Cracking or collapsing is a clear sign of instability that you should heed.  Keep in mind that there is an older hard slab problem stacked beneath the recent storm snow on some leeward terrain features, triggering an avalanche in the storm snow could release a hard slab below like in this ob from Schuylkill Ridge yesterday.  Use caution around drifted terrain today as the storm snow may be very sensitive and it is now very hard to tell if an old slab exists below the recent storm.

Sheltered Terrain:  You can be confident that steep, sheltered terrain facing the north half of the compass will produce moving snow.  The question is will it be a shallow soft slab or simply a loose avalanche.  Either way, the new snow will add volume to avalanches as they run and accumulate mass.  Expect avalanches to be large enough to hurt you or potentially bury you in snow-favored areas or long, continuous slopes.  Sheltered terrain facing the south half of the compass could produce small avalanches but are much less likely and will be smaller in size due to crust below the storm snow.

Although this storm was not all that impressive, it will bring a fairly distinct increase in avalanche danger for areas that accumulated the most storm snow.  Take a cautious approach to the day to make sense of the conditions you are traveling through and expect things to be different from what you have been managing the past few weeks.

 

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