Bollettino valanghe

Northwest Mountains

Crested Butte Avalanche Center
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Pericolo valanghe

Thu
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
2 · Moderato
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In sintesi

You can trigger a dangerous slab avalanche several feet thick near and above treeline.  The most recent natural avalanche ran on Mount Emmons Monday night.  Lower elevation, wind-protected northerly slopes offer less risky options as fewer avalanches have been documented this past week.  Warming temperatures and solar radiation will wet snow surfaces primarily on the south half of the compass.  Expect to trigger wet avalanches on steep slopes once you encounter more than a few inches of slushy snow.  Wet avalanches might grow to a large size today.

Problemi valanghivi

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    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.  

    (4/2/2024). Recent Persistent Slab avalanches in Redwell Basin on Mount Emmons.

    Photo: Eric Murrow

  • Loose Wet

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    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.  Wednesday's 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 present wet and dry avalanche problems.  After a week of snowy and windy weather, expect to find the most hazardous conditions for the Persistent Slab problem at upper elevations and on wind-drifted slopes.  The documented avalanche data from the past week points to northerly-facing slopes and possibly high-elevation southeast slopes as the most problematic.  A forecaster experienced a collapse and propagating test results on this interface on Tuesday near Mount Baldy.   The weak layer responsible for the recent activity is commonly 2 to 3 feet deep and could produce a large avalanche.  Below treeline slabs are less developed and weak layers are less common.  This results in a lower likelihood of Persistent Slab avalanches at lower elevations.  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 create a wet loose problem on Wednesday.  Tuesday's high temperatures were too cool for a significant problem, but high temperatures may increase by 4 to 7 degrees today.  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 in optimal conditions.  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.

The warming trend continues on Wednesday and Thursday.  Expect wet avalanche concerns to increase each day.  Forecasters have discussed the possibility of Wet Slab conditions to develop this week as crusts and facets in the upper snowpack could be flooded with meltwater.  The danger trend was set to CONSIDERABLE for Thursday as wet problems increase in size and frequency.

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