Bollettino valanghe

Northwest Mountains

Crested Butte Avalanche Center
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Pericolo valanghe

Wed
Alta quota
2 · Moderato
Limite del bosco
1 · Debole
Sotto il limite
1 · Debole
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Non aggiornato — questo bollettino è scaduto 5 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

A small storm delivered 1-3 inches below treeline with a chance for an inch or two more in the alpine accompanied by moderate westerly winds at ridgetops.  Anticipate finding shallow yet sensitive drifted slabs on leeward features at upper elevations particularly on slopes with a northerly-facing component where fragile weak layers exist.  Identify leeward terrain features and monitor new snow accumulations and if you find 6 inches or more of new snow, you should expect that human-triggered avalanches are possible.

Problemi valanghivi

  • Wind Slabs

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

    New snow accumulations are rather modest,  but westerly winds have helped to form fresh slabs on leeward terrain features at upper elevations.  You are most likely to find newly formed slabs immediately below ridgetops, underneath cornices, and tucked behind rock outcrops/tree fences.  The most suspect slopes for Wind Slab formation previously possessed very weak and fragile snow surfaces which will help create slabs that are sensitive to the weight of a person.  Given the weak old snow surfaces, expect to be able to trigger avalanches that are thinner than you are accustomed to.  Avalanches are possible with as little as 6 inches of new or wind-blown snow.  

    An example of a Wind Slab avalanche tucked below an alpine peak immediately beneath a cornice.  This is a good example of the most suspect terrain today for triggering an avalanche. 

Avalanche Discussion

Snow totals overnight are a bit underwhelming with only 3 inches observed below treeline however, westerly winds have drifted snow at upper elevations, and the old snow surfaces are weak and fragile after a nearly two-week dry period.  The old, weak snow surfaces have been thoroughly documented in recent observations (Northwest Mountains, Southeast Mountains, additionally you can watch the video in the media gallery below).  Prior to the current storm, the missing ingredient for avalanches has been a slab.  Last night's snowfall and westerly winds have likely formed slabs at upper elevations on leeward terrain features.  The combination of well-documented weak layers and newly formed slabs means that a genuine avalanche problem exists.  Given the exceptionally fragile nature of the current weak layers expect that you may be able to trigger avalanches that are much thinner than you expect or normally encounter.  You may find fresh drifts on slopes that had melt/freeze crusts as well (for example some east and southeast slopes), but these locations are not expected to be nearly as sensitive as those on the north half of the compass.  It appears as though more snow has fallen in the Northwest Mountains than in the Southeast Mountains so the problem will be found in more locations and be a bit larger in size in the Northwest Mountains.  Most avalanche activity is expected to remain small in size, but leeward slopes with efficient fetches and snow favored areas in the Northwest Mountains may creep close to large size avalanches.

Your best defense for managing today's problem will be to closely monitor new snow accumulations and identify and avoid terrain the appears to have fresh drifting.  6 inches of new or wind-drifted snow is a good threshold for finding increased avalanche hazard.  Use a bit of extra caution today at upper elevations as the sensitivity of the Wind Slab problem may be a bit surprising.

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