Bollettino valanghe

Southeast Mountains

Crested Butte Avalanche Center
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Pericolo valanghe

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2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
2 · Moderato
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Non aggiornato — questo bollettino è scaduto 3 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

Persistent slab avalanche concerns remain a lingering and stubborn problem. Producing one of these avalanches that breaks into the middle of the snowpack will typically need a large load or just the right trigger point. A quick-hitting storm arriving today will begin building a fresh round of small wind slabs later this afternoon. Continue to use travel techniques to your advantage with regrouping areas safe from an avalanche that could be larger than you expect, and keep an eye out for developing wind slabs later today. 

Problemi valanghivi

  • Persistent Slabs

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

    Over the past couple of weeks, several large avalanches have failed on faceted weak layers deeper in the snowpack. These include a natural avalanche on Carbonate Hil, a remotely triggered avalanche on Mt. Emmons on Sunday, and several human-triggered slides the previous week (Hunter Hill, Snowmass). Persistent slab activity has been infrequent this month and most problematic on wind-loaded terrain. Last week's loading event produced surprisingly little avalanche activity and adds to the infrequent characterization of this avalanche problem recently. 

    At below treeline elevations, there are some areas in the SE Mountains that have seen a foot of snow accumulate on a weak old snow surface. In general, the slabs above that weak snow remain soft and may not be enough to propagate a slab avalanche. In open areas at these lower elevations past winds will have stiffened those slabs or created thicker slabs in some areas that will be more reactive to human triggering. If you are riding steep below treeline slopes, keep an eye on these slab/weak layer characteristics. 

    2/23:  A surprising collapse that broke around 3 feet deep into the snowpack on northeast-facing terrain on Mount Emmons.

  • Wind Slabs

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

    Around mid-day, we'll see winds increasing from the southwest and the west, with the arrival of a quick-hitting storm. By the end of the day, we'll see new snow accumulations in the 1 to 3" range that will add fuel for the new round of wind slabs that will develop through the day. Given the low snow volume that will be available for transport, these new wind slabs will be small in size.

    An example of a wind slab hanging out below a ridgeline. 

Avalanche Discussion

In general, we are saying out with the old and into the new, as we have moved away from one snowy and windy week, and into a new snowy/windy week. Yesterday's warm temperatures and mild weather was a nice break that allowed last week's new snow avalanche problems to settle out. 

NW Mountains: Concerns for persistent slab avalanches breaking in the upper half of the snowpack have decreased. It's important to understand that we do have a layered upper snowpack with some potential weak layers creeping about. However, you are likely going to need to find an isolated area where the snowpack is abnormally shallow and weak, or a large load to produce an avalanche that breaks into those layers. Today's storm will be interesting to see how it plays out. 3" to 6" of snow in a 4hr to 6hr period will make for some high precipitation rates if we see the upper end of that snow forecast. Combine those potential precipitation rates with elevated winds and, we would see some quickly changing avalanche conditions. If we don't see the upper end of that snow forecast then we may see some changes in the avalanche danger rating for below-treeline elevations tomorrow. The new round of wind slabs that develop today will continue to be in the headlines tomorrow. 

SE Mountains: Persistent slabs are the primary avalanche problem until we get more snow later this coming week. As explained this avalanche problem has been infrequent this month but has still produced some surprising avalanches. The main change has been the addition of below treeline elevations to the problem rose. Those elevations have become weak over the last month with cold temperatures and little accumulating snow. Some parts of the forecast area, received around a foot of snow last week and are developing a new persistent slab avalanche problem. Today's forecasted snow amounts will just barely be enough for a new round of small wind slabs to form.

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