Boletín de aludes

Northwest Mountains

Crested Butte Avalanche Center
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Peligro de aludes

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

Lo esencial

You can encounter sensitive drifts at upper elevations formed by fresh snow and gusty winds.  Identify leeward terrain features with recent or ongoing drifting and avoid those areas to reduce the chance of triggering an avalanche in the new snow.  There is a smaller chance that you trigger an avalanche on old weak layers deeper in the snowpack on some slopes facing the north half of the compass.  Although harder to trigger, an avalanche failing on deep weak layers would be dangerously large.  Wind-sheltered areas are less problematic, particularly on the sunny side of the compass.   

Problemas de aludes

  • Wind Slabs

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

    As of 5 am, some weather stations show 10 inches of new snow with a few more inches possible today.  Gusty northwest winds will build slabs on leeward terrain features at upper elevations.  The most problematic slopes are above treeline, but some drifting may extend into lower elevations.  Expect to find fresh slabs underneath cornices, below ridge tops, and cross-loaded in gullies.   Carefully read the terrain to identify drifts.  You can often feel an increased stiffness when you encounter wind-loaded snow.  Shooting cracks are a clear sign of unstable snow.  Avalanche size often remains small, but some well-drifted features could reach a large size.  There is an outside chance that a Wind Slab could step down and trigger a deeper Persistent Slab where the two problems overlap. 

    A Wind Slab avalanche from earlier this season that exemplifies the most likely terrain to encounter a freshly drifted slab: a leeward slope beneath an alpine ridgeline.

    Photo: Crested Butte Avalanche Center

  • Persistent Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Possible
    Tamaño
    2–3

    Weak facets, depth hoar, or collapsible crusts exist on the northern half of the compass.  Slabs on top of these weak layers average 1.5 to 3 feet thick in wind-sheltered terrain. Slabs are thicker and harder in wind-drifted terrain and can step down through older slabs to the ground.    This problem has become stubborn to triggers, often requiring a thin spot on the slope, such as near buried rocks, trees, or where slabs thin from wind effects. Avalanches can break widely across multiple terrain features and be remotely triggered from flat terrain near or below steep slopes without warning signs. The problem can be avoided on slope angles consistently less than about 30 degrees.  

    The current storm could slightly increase the sensitivity of the Persistent Slab problem on a few isolated slopes that experience extensive wind loading. 

    A couple of persistent slab avalanches were remotely triggered in the upper Cement Creek area on Friday, 2/28. 

Avalanche Discussion

Winter returns on Tuesday with a modest refresh of snowfall and northwest winds.  Storm totals vary significantly across the forecast zones, with the largest totals coming from the Ruby Range in the Northwest Mountains (up to 10 inches early this morning).  Lesser amounts accumulated in the Southeast Mountains with 2 to 4 inches.  Expect the winds to efficiently drift the new snow in both zones, but snow-favored areas will have a higher risk due to larger slab size and greater distribution.  In the Northwest Mountains, there is just enough snow that a few heavily drifted slopes could produce a large avalanche in the storm snow.  In the Southeast Mountains, avalanches in the storm snow are likely to remain small in size.  A reasonable rule of thumb would be to exercise caution when you encounter or expect to encounter about 10 inches or more of new/wind-blown snow.

The older Persistent Slab problem remains Possible in both forecast areas.  There is a chance that you release an avalanche on weak layers buried earlier in the winter if you were to find a trigger point on a slope.  One of these avalanches won't give a warning before releasing.  If you choose to travel on steep slopes highlighted by the Persistent Slab rose, avoid places with obvious signs of wind effect and rocky areas to reduce the chance of finding a shallower spot in the snowpack.  Trigger points can often be hidden in the snowpack without visual clues at the surface.  Slopes with a uniform appearance could hide trigger points like buried rocks or bushes.  You can reduce risk by selecting small slopes without terrain traps to lower the consequences if you take a ride in an avalanche.  The current storm is not expected to impact the Persistent Slab problem significantly. Still, we couldn't rule out a Wind Slab stepping down into older weak layers or a minor increase in sensitivity on northerly slopes where the most storm snow accumulates.  

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