Bollettino valanghe

Northwest Mountains

Crested Butte Avalanche Center
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Pericolo valanghe

Wed
Alta quota
3 · Marcato
Limite del bosco
2 · Moderato
Sotto il limite
2 · Moderato
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Non aggiornato — questo bollettino è scaduto 2 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

Over a foot of recent snowfall and efficient winds created sensitive avalanche conditions on drifted terrain, particularly on northerly slopes where storm snow fell on a faceted weak layer.  Soft slab avalanches may be possible in sheltered areas as well.  Cracking is a clear sign of a problem in wind-sheltered places.  Use caution at upper elevations and avoid drifted terrain features to reduce your risk of triggering an avalanche.

Problemi valanghivi

  • Storm Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–2

    Recent snow totals exceed a foot (reports of 15" in the Anthracite Range) around the Northwest Mountains.  The most concerning slopes will be drifted terrain features at upper elevations.  The new snow accumulated above crusts on the south half of the compass and small-grained facets on the north half of the compass.  Avoid terrain where you expect to find drifting.  Carefully assess the recent storm snow in sheltered areas.  You can use small test slopes on wind-protected terrain to investigate for instabilities in the storm snow and how well it bonded to the old snow surface.  Cracking in the new snow is a sure sign of a slab avalanche problem.

    (3/25/2024)

    A skier-triggered avalanche from the Anthracite Range on Monday.  Expect similar type conditions where you find about a foot or more of new snow on northerly slopes.

     

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Unlikely
    Dimensione
    2–2.5

    In the Northwest Mountains, high-consequence slabs breaking on older weak layers have become isolated and difficult to trigger. The last observed persistent slab avalanche occurred on March 8th in this forecast area. Any lingering persistent slabs would most likely be triggered from an unusually shallow or previously wind-eroded slope where the total snowpack height is below average.  Large cornice falls could act as triggers as well. Persistent slab avalanches can be remotely triggered from low-angle terrain and break deeper and wider than you might expect.  Slope angles consistently less than 30 degrees are a reliable way to avoid the problem when in doubt.  

    The crown of a very large persistent slab remotely triggered by snowmobiles on March 8.  This slope is west facing and eroded by seasonal winds, making for a shallower and more problematic snowpack than other slopes. 

Avalanche Discussion

A slow trickle of snow continues to add volume to storm totals since Saturday night.  Favored locations in the Northwest Mountains exceed a foot with a report of 15 inches in the Antracite Range.  Totals decrease in the Southeast Mountains and are generally less than a foot.

The primary problem in the Northwest Mountains will be managing the recent storm snow.  Expect to find sensitive avalanche conditions where you encounter wind-deposited snow on leeward terrain features.  Observations from Sunday pointed to a developing problem with a triggered avalanche on Mount Emmons, cracking in drifted snow on Anthracite Mesa, and multiple triggered avalanches from the Marble area (1,2,3,4); on Monday triggered avalanches on Axtel and in the Anthracite Range further support an avalanche problem where you find around 1 foot or more of new or windblown snow.  The recent snow fell on a layer of near-surface facets on the north half of the compass, expect conditions to remain sensitive today as a persistent weak layer is responsible for failure below the new snow.  There is uncertainty about the conditions in sheltered terrain, but use caution if you ride in steep, wind-sheltered northerly terrain and carefully assess the storm snow interface.  The storm snow appears to have bonded better where it landed on crusts.

In the Southeast Mountains, there are two problems to manage.  The first is avalanches in the storm snow as mentioned above but there is less storm snow in the Southeast Mountains.  Finding trouble in the storm snow will be more commonly found in drifted terrain and less likely in sheltered areas.  Secondly, the Persistent Slab problem could become more sensitive with the recent loading.  Your best bet is to avoid drifted terrain features highlighted by the Persistent Slab rose as triggering an avalanche that breaks deeply in the snowpack remains possible and would be very dangerous. 

Pay attention to warming snow on sunny slopes if the sun makes an appearance.  Strong, spring-time radiation can quickly heat sunny terrain and cause the new snow to shed from steep sun-exposed slopes.

 

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