Bulletin d’avalanche

Northwest Mountains

Crested Butte Avalanche Center
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Danger d’avalanche

Tue
Alpin
3 · Marqué
Limite forestière
3 · Marqué
Sous la limite
3 · Marqué
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Périmé — ce bulletin a expiré 6 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

The avalanche danger will rise to CONSIDERABLE by this evening and may reach HIGH later tonight.   New snow over the next 24 hours will tip our fragile snowpack beyond its breaking point again, as it has done with every previous storm this month.  You can trigger slab avalanches up to several feet thick today.  Instabilities will become more widespread and avalanches will start to fail naturally by this evening.  Dangerous avalanche conditions are expected to develop around sundown, coinciding with the arrival of intense snowfall.  Expect changing conditions later today and choose more conservative terrain options as snow totals surmount 6" or more.  

Problèmes avalancheux

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    2

    Persistent slabs will become increasingly sensitive to human and natural triggers as new snow and windloading adds stress to the snowpack.  Collapses and shooting cracks are clear warning signs of danger.   The problem is most reactive on below treeline slopes that face the northern half of the compass, where you can find soft slabs one to two feet thick over old, weak snow.  Near and above treeline, slabs are thicker, harder, and more localized to wind loaded terrain features. They are tougher to trigger, but more consequential.  In either case, you can easily avoid the problem by choosing slope angles less than 30 degrees that aren't connected to steeper terrain above.  

  • Storm Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    1

    Intense snowfall rates around sunset may spur storm slab instabilities involving new and recent snow.  The problem is unlikely to develop until late in the day.  Monitor storm accumulations. If you see more than 6" of new snow, small slabs in the upper snowpack can be triggered on steep rollovers or windloaded terrain features.  These will fail on weak layers and crusts at or just below this morning's snow surface.  Any storm instabilities that develop today will be small, but they can cause trouble if they push you into a terrain trap or trigger a larger persistent slab avalanche.  

Avalanche Discussion

We're staring down the barrel of the next storm system and avalanche cycle.  Snowfall will be slow to ramp up today, and through most of the daylight hours, the danger should hang tough at MODERATE.  Triggering persistent slabs will be possible on some terrain features.  Lurking instabilities are generally on steep windsheltered terrain on the northern half of the compass that hasn't already avalanched or on previously windloaded terrain features near and above treeline.  Heavy snowfall around sunset will increase the likelihood of persistent slabs and storm slabs, and quickly ramp the danger up to CONSIDERABLE.  We are showing this late-day anticipated change in the forecasted danger and problems above.  If the storm overproduces, the danger may rise to HIGH during the peak of the storm around midnight.  An AVALANCHE WATCH is in effect.  

 Our persistent weak layers have proven, time and time again, that they can not handle even mild loading events.  Yesterday's observations included more collapses and triggered persistent slabs.  The snowpack is weakest below treeline, and I expect we'll start to see natural avalanche activity, both at the snow surface and on weak layers near the ground, as soon as storm totals reach 4" to 6".  This looks like it will happen near or shortly after sunset.  The alpine has been worked hard by winds last week, making for thicker, more localized persistent slabs.  Instabilities in the alpine are most likely to involve just today's new and wind drifted snow at first.  Once storm totals start reaching a foot or more, I'm nervous about larger slides breaking across alpine start zones, similar to the avalanches we saw last week on Mt. Richmond.    The timing and severity of increasing danger hinges directly on how potent this storm is.  Pay attention to storm totals today and expect natural avalanche activity to be on the rise tonight.  

Régions couvertes