Boletín de aludes

Northwest Mountains

Crested Butte Avalanche Center
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Peligro de aludes

Mon
Alta montaña
3 · Notable
Límite del bosque
3 · Notable
Bajo el límite
2 · Moderado
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Desactualizado: este boletín caducó 3 years ago. Estás viendo condiciones pasadas, no el boletín vigente.

Lo esencial

Increasing winds today will add stress to leeward slopes and form fresh wind slabs: stay off of steep slopes receiving active wind loading.  On some west to north to easterly facing terrain features, you can trigger a large and deadly avalanche several feet thick at any elevation.  The safest riding is in simple terrain or on wind-sheltered, southerly aspects. 

Problemas de aludes

  • Persistent Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Possible
    Tamaño
    1–2.5

    Slabs 1 to 4 feet thick have formed over several persistent weak layers in the snowpack:  Facets and depth hoar near the ground and surface hoar layers in the upper snowpack. The problem has been most active on northerly and easterly facing slopes, with some avalanches on westerly facing terrain as well. Persistent slabs are gradually becoming more difficult to trigger; although today's drifting snow will stress some leeward or crossloaded terrain.  Persistent slabs could break wider than you expect, and they can be triggered from flat slopes connected to steeper terrain above you. You can reduce your risk by traveling on slopes where the problem isn't highlighted above, or by traveling on small terrain features without terrain traps.  You can avoid the problem on slopes consistently less than 30 degrees.    

    12/8: The flank of a persistent slab avalanche that was remotely triggered from lower on the slope.  

  • Wind Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Likely
    Tamaño
    1–2

    Increasing northwesterly winds will drift the recent snow into sensitive wind slabs today.  Look for blowing snow and thicker feeling drifts to alert you to the problem. Fresh wind slabs will be forming below leeward ridgelines and in cross-loaded terrain features such as gullies or behind tree fences.    Seek out wind-protected terrain to avoid the problem.  

    A small wind slab from earlier this weekend.  Wind slabs are expected to be more widespread and grow a bit larger today.  

Avalanche Discussion

Alpine winds are increasing into the 20's and 30's with stronger gusts out of the northwest.  There is more snow available for transport in the Northwest Mountains, so fresh wind slabs are expected to grow up to D2 in size in terrain with productive fetches.  Elsewhere, most wind slabs are expected to be relatively small, D1-1.5.

Friday's storm produced .6 to 1.1" SWE (6" to 16") across the forecast area, favoring the Northwest Mountains.  This was about half the load compared to last weekend's storm, and thankfully, our forecast team and public observers did not spot any avalanches breaking into old layers. That's in contrast to every other storm we've seen this winter, and in contrast to the rampant activity from last weekend's storm.  This supports snowpack observations over the past few days of a gradual decrease in the sensitivity of our persistent slab problem.  However, today's increasing northwesterly winds will test a few suspect aspects at higher elevations: east to southeast facing terrain and crossloaded terrain features elsewhere.   Although signs of instability on our deep weak layers are gradually diminishing, we remain quite cautious of the terrain highlighted by the persistent slab rose, especially slopes getting windloaded today.  The destructive size remains the same: slabs up to several feet thick.  We've also rolled our most recent storm snow over surface hoar concerns into the persistent slab problem.  This newly developing issue is most concerning in the snow-favored Northwest Mountains, on shady, wind-protected slopes near and below treeline, described in this observation yesterday.  

Last week's warm spell added some strength to the upper snowpack on southerly aspects.  These same aspects have fewer and less developed weak layers in the snowpack.  Wind-sheltered slopes on the southern quadrant offer a safer alternative to traveling on west, north, or east-facing terrain.  Avoid fresh wind slabs and look for thick, supportive crusts below the recent snow for a more trustworthy snowpack.   High southeast aspects tend to stay colder than the rest of the southerly aspects; thus we still have some concerns about collapsible crusts a couple of feet deep in terrain like Red Lady Bowl, especially with the bullseye of today's wind-loading pointed at that terrain.    

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