Bollettino valanghe

Southeast Mountains

Crested Butte Avalanche Center
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Pericolo valanghe

Thu
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
2 · Moderato
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In sintesi

Remote weather stations are reporting 24-hour snow totals varying drastically between 1 and 7 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 concerns.

Problemi valanghivi

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    2–2.5

    In the Southeast Mountains, the last round of persistent slab avalanches occurred on March 16th. The most prominent weak layers are surface hoar buried a couple of feet deep and depth hoar near the ground.  The snowfall and windloading may increase the sensitivity of deeply buried weak layers.   Poor snowpack structure still exists in some areas and is commonly associated with a total snowpack height between 80 and 170cm. Persistent slab avalanches can be remotely triggered from low-angle terrain and break deeper and wider than you might expect.   Persistent slab avalanches are unlikely on southerly aspects, or areas where the snowpack is consistently deeper than 200 cm.  Slope angles consistently less than 30 degrees are a reliable way to avoid the problem. 

    A large persistent slab on Mt. Crested Butte that ran on 3/16.  This slope is shallow, variable in depth, and on the north half of the compass: a combination of ingredients to consider avoiding.

  • Storm Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    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 around 1 foot 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 in the NW Mountain forecast area.

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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