Lawinenlagebericht

Northwest Mountains

Crested Butte Avalanche Center
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Lawinengefahr

Wed
Hochgebirge
2 · Mässig
Waldgrenze
2 · Mässig
Unterhalb
2 · Mässig
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Kernpunkte

You can trigger a slab avalanche up to several feet thick.  This problem is more commonly found at upper elevations and wind-drifted features.  Natural avalanche activity diminished on Monday after multiple days with large natural avalanches.  Less problematic conditions can be found in wind-protected terrain at lower elevations.  Warming temperatures and a strong April sun will wet snow surfaces primarily on the south half of the compass.  Expect to trigger loose avalanches once you encounter more than a couple of inches of wet, cohesionless snow on sunbaked slopes.

Lawinenprobleme

  • Persistent Slabs

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

    Snow and wind-loading in the past week have formed a new generation of slabs up to several feet thick over small-grained facets in the upper snowpack.  Numerous large slab avalanches have occurred on this layer in the past week.  Slabs are larger and most active near and above treeline on wind-loaded slopes, especially on colder aspects.  For a safer day, avoid recently windloaded slopes while staying alert for potential instabilities on wind-sheltered terrain.  

    On unusually shallow slopes, most commonly in the Southeast Mountains, there is still a small potential to trigger a destructive avalanche that breaks on deeper weak layers. The most concerning structures are on northerly aspects near and above treeline where snow depths are less than 170 cm, or where large cornices fall onto slopes.  

    A large persistent slab in Racoon Basin triggered by a shallow windslab on Sunday.  

  • Loose Wet

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

    Warming temperatures and strong solar radiation will wet snow surfaces on the south half of the compass and possibly low elevation northerly aspects.  Recent winter storms have left dry snow on many aspects and elevations for loose avalanches to entrain.  Tuesday's modest warm-up under northerly flow may limit size, but given there's ample snow for entrainment loose avalanches could grow large today.  You can manage the risk by riding on sunny slopes earlier in the day, by following the warming conditions from east to south to west as the day progresses, or by sticking to wind-sheltered northerly slopes with cold, dry surfaces. 

    A Wet Loose avalanche from a few weeks ago.  Expect similar-sized avalanches to become possible today by the late morning or early afternoon on sunbaked slopes.

    Photo: Evan Ross

Avalanche Discussion

A beautiful spring day will require you to manage both wet and dry avalanche problems.  A week of stormy weather just ended along with natural slab avalanche activity.  Expect to find the most hazardous conditions for the Persistent Slab problem at upper elevations and on wind-drifted slopes.  Take a look at the documented avalanche data from the past week.  It points to increased trouble at higher elevations and on leeward terrain.  The weak layer responsible for the recent activity is commonly 2 to 3 feet deep which provides enough volume for large avalanches.  Slabs are less developed and the weak layers are less common below treeline making for a lower likelihood of triggering an avalanche.  There have been a couple of human-triggered avalanches below treeline in the Northwest Mountains this past week so maintain your guard on unsupported features or isolated slopes with wind loading at lower elevations.

Sunny skies and rising temperatures are sure to create a wet loose problem on Tuesday.  The biggest question is how large will loose avalanches grow and do temperatures warm enough for avalanches to spread to low-elevation northerly aspects.  Additionally, there is some distribution overlap between the Wet Loose and Persistent Slab problem.  For example, on a below treeline east slope you could trigger a wet loose in the surface snow that pries out the Persistent Slab problem as it descends.  Manage wet snow problems by starting your day early and catching sunny slopes at the optimal time.  A supportive snowpack with just an inch or two of sun-softened snow is ideal for riding conditions and safety.  East slopes will warm first followed by south and finally westerly terrain in the afternoon.

Temperatures continue to rise on Wednesday and Thursday.  Expect wet avalanche concerns to escalate day after day.  As temperatures begin to soar during the middle of the week, Wet Slab avalanche conditions may develop as meltwater floods the persistent weak layers and crusts a few feet deep.  If you plan to travel on or below steep, sunny terrain, then expect to start your days earlier to manage wet snow problems.

 

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