Bollettino valanghe

Northwest Mountains

Crested Butte Avalanche Center
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Pericolo valanghe

Mon
Alta quota
3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
2 · Moderato
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Non aggiornato — questo bollettino è scaduto 8 months ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

Dangerous avalanche conditions exist, requiring cautious route-finding and conservative decision-making to manage a diverse list of avalanche problems. Yesterday, a couple of storm slab avalanches ran naturally on upper-elevation south-facing slopes from warming temperatures. While the most serious avalanche concern exists on northerly and easterly-facing slopes, where widely propagating persistent slab avalanches can be triggered. Multiple skiers were caught and carried in these types of avalanches on Friday. Lower elevations have a lower likelihood of triggering these avalanche problems, while low-angle terrain remains another easy way to avoid them and enjoy the backcountry. 

 

Problemi valanghivi

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    1.5–2.5

    The snowpack on the north side of the compass holds a variable mix of weak snow. The primary layers of concern are facets in the bottom half of the snowpack from the December drought, and a colasable crust near ~10,000ft and ~11,000ft created by a rain event on Christmas day. Persistent weak layers have been further documented on some high-elevation southeasterly facing slopes. An extensive natural avalanche cycle occurred on Friday, while many more human-triggered avalanches were triggered in the past few days. This snowpack structure is variable due to past wind events and well-above-average temperatures. This variability can create inconsistent feedback and problem distribution. So, obvious signs of instability may not provide reliable feedback before you trigger a dangerous avalanche.  You can reliably avoid the problem by choosing slopes less than 30 degrees and not connected to steeper slopes above, or head to sunnier aspects where sensitive weak layers are less common.

    This avalanche problem becomes less likely to trigger at lower elevations due to thicker crusts buried in the snowpack on all aspects. Continue to carefully evaluate your local terrain, as variability can exist across the forecast area. 

    A complex mix of storm slab and persistent slab avalanches between Purple and Afley in the Ruby Range. These avalanches are estimated to have run on Friday, 2/2. 

     

  • Storm Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–2

    Last Friday's storm created thick slabs around the compass. These slabs have become notably more stubborn to human triggering over the last couple of days, and will most likely not provide obvious signs of instability. Continue to exercise caution at upper elevations where this avalanche problem will take the longest to heal. The unseasonably warm temperatures today may create a hybrid spring-like avalanche problem on steep southerly-facing slopes, such as a wet loose avalanche or roller balls that could trigger a wider slab avalanche.

    A pair of storm slabs that ran naturally on Saturday. They were triggered by roller balls or wet loose avalanches from above. South side of Ruby Peak. 2/2. 

Avalanche Discussion

Good visibility on Saturday allowed us to gather data on the recent avalanche cycle. Storm slab avalanches occurred around the compass, and we have spent less time documenting those avalanches as they are continuing to heal. The persistent avalanche problem deserves focus, as it will be the lasting problem. The avalanche cycle between 1/1 and 1/3, has 58 documented avalanches so far. If we filter that data to include only avalanches labeled as persistent slabs, we are down to 38 documented avalanches. This data highlights the "most likely" areas where this avalanche problem exists. Northerly and easterly facing slopes at near and above treeline elevations. These avalanches paint the bullseye for the most dangerous terrain, but of course, there will be outliers. Persistent weak layers exist on other aspects, and the snowpack structure on those other aspects has simply made them comparitbly less reactive. 

Comparing the avalanche data between the two forecast areas, there has been significantly more avalanche activity documented in the NW Mountain forecast area than in the SE Mountain forecast area. While there haven't been any observations in upper Brush Creek or upper Cement Creek, the primary reason for the difference in avalanche activity was the amount of load that occurred during the last storm. Measured snow totals in the NW Mountains have been up to 1.5" of SWE. In comparison, the SE Mountains had accumulations in the .6 to .8 SWE range. Of course, more snow accumulated at higher elevations or at different locations in those forecast areas, but that helps show the difference between the forecast areas. 

Regioni coperte