Boletín de aludes

Northwest Mountains

Crested Butte Avalanche Center
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Peligro de aludes

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

Lo esencial

Remote weather stations are reporting 24-hour snow totals varying drastically between 6 and 22 inches. West to Northwest winds since last Sunday, have formed wind slabs on the lee sides of ridgelines and cross-loaded terrain features. While in wind-sheltered locations you can expect loose snow avalanches and the potential for soft storm slab avalanches. The storm slab avalanche problem will be most common on northerly-facing slopes. Riding in avalanche terrain today will require you to first manage wind-loaded terrain and second evaluate the new snow for smaller loose snow avalanches versus the larger slab avalanche problems.

Problemas de aludes

  • Storm Slabs

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

    The potential for storm slab avalanches is the most widespread on northerly-facing slopes where a layer of small facets were buried last weekend. Those potential slabs are now 1 to 2 feet thick. In other areas, storm slabs releasing within the storm snow are possible, though you most likely find yourself managing previous wind-loading and wind slabs near ridgelines and cross-loaded terrain featuers. Assessing these different avalanche problems will be required before riding in steep avalanche terrain today. Look for small test slopes to get a feel for the avalanche problems in your area. 

    This storm slab was human-triggered yesterday near Purple Ridge. There is now another 6 to 12 inches of snow on top of this avalanche problem.

  • Persistent Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Unlikely
    Tamaño
    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

24-hour snow totals are variable across both forecast areas. The best guess is that a convective storm rolled through last night and created some good snow accumulations in some areas, while other areas not far away got skunked. Below are those 24-hour storm totals from remote weather stations. 

NW Mountains: Schofield Pass .1" SWE, Irwin area 1" SWE and 12 to 22" snow. Purple Ridge 6 to 8" snow. 

SE Mountains: CBMR Pow Cam 7" snow. Butte Snowtel .4" SWE. West Brush Creek at 11,000ft 1" snow. 

With a huge variation in 24-hour storm accumulations, it is difficult to fit the avalanche problem into one primary box. You will need to investigate the avalanche conditions in your local area before committing to steep avalanche terrain. As previously described, you can encounter storm slabs, wind slabs, and loose snow avalanches. Observations over the last several days have noted small facets that were buried last weekend on northerly-facing slopes. In the Anthracite there was a small storm slab that likely ran on this interface, and yesterday a couple of storm slabs were human-triggered near Purple Ridge. We can expect continued issues with soft storm slabs releasing on these facets over the coming days. In other areas like southerly facing slopes, the storm snow has been bonding ok to the old crusts that were buried last weekend. However, density changes between the recent storms could also create a storm slab issue on those aspects too. Upper elevations have seen blowing snow and wind-loading through the week. West to northwest winds were fairly light last night and look to remain light for most of the day today. We may further see some moderate to strong wind gusts mixing in this afternoon and tonight. 

Lastly, if the sun comes out in force this afternoon, pay attention to warming snow on southerly to westerly aspects.  We expect to move into more of a wet loose avalanche problem on Thursday with warming temperatures and a longer period of clear sky. 

 

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