Bollettino valanghe

Northwest Mountains

Crested Butte Avalanche Center
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Pericolo valanghe

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

In sintesi

The avalanche danger is currently driven by the previous wind-loading that has occurred during the last week. Wind slabs have generally become stubborn and more difficult to trigger, and you may not observe obvious signs of instability. Make a plan with your group on how to either manage or avoid this avalanche problem. In wind-sheltered areas at below treeline elevations, you can expect to find normal caution conditions. At these lower elevations, avalanche problems are mostly confined to some extreme terrain and a few cross-loaded terrain features. 

Problemi valanghivi

  • Wind Slabs

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

    The wind has been mostly calm to light for greater than 24hr now. While in the alpine there have still been wind gusts into the 20's from the west and north. You could find an isolated wind slab that has freshly formed and is more reactive, but in the big picture, this avalanche problem is stubborn and more difficult to trigger. Earlier this week we had an extreme wind event from the southwest, with continued strong winds into Wednesday. Those old slabs will still require some consideration near ridgelines and cross-loaded terrain features. The recent avalanche activity from this last week is well documented in the observations tab. 

    This recent avalanche has a combination of terrain characteristics that you would still want to avoid. The slope is wind-loaded, steep, and unsupported by the rollover below the crown.

  • Persistent Slabs

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

    There are several layers of small-grained facets in the upper few feet of the snowpack that have created a lingering low probability of an avalanche stepping down into these deeper layers. In most cases, we would need a significant trigger such as a cornice falling onto a suspect slope. A human could more likely be the trigger in an unusually shallow or rocky area where there is a thinner slab over weak snow. 

    A persistent slab that ran in the last week on a shallow slope off East Beckwith. 

Avalanche Discussion

West Elk Air has come through many times now to help the forecast team document avalanche activity after notable weather events. Big thanks to them, as it is really helpful for us all to have this data. On a daily basis, public observers continue to send in detailed observations while we also have local avalanche forecasters in the air and on the ground. We sure have something special going on in this valley. 

 

So what did we learn from all the avalanche data we received yesterday? This past week was characterized by an extreme wind event from the southwest, combined with 1 to 2 feet of snow across the forecast area. We expected some amount of natural avalanche activity with avalanches releasing in the new snow and in some areas breaking into persistent weak layers. The avalanche size was in the D1 to D2 range and not large enough or widespread enough to have pushed us into HIGH avalanche danger or an avalanche warning. 

In the NW Mountains, some cornices fell, and both wind slab and storm slab avalanches released, up to D2 in size. The persistent slab avalanche problem was listed at unlikely, and we have only observed avalanches stepping down into deeper weak layers in one location so far. This was on a steep slope that held a below-average snowpack height due to past avalanche activity. Zach had previously documented the weak snow in this area back in mid-February.

In the SE Mountains, the avalanche activity was mostly the same with cornices releasing and both wind slab and storm slab avalanches to D2 in size. However, there were more avalanches that stepped down into persistent weak layers. The persistent slab avalanche problem has been in the "possible" category for some time now, and that is a step higher on that likelihood scale than the NW Mountain forecast. The most common areas where persistent slab avalanches were observed, were below cornices and in steep rocky terrain. 

All the recent avalanche data can be viewed in the observations tab, avalanche table and the avalanche rose. 

 

Looking ahead to the weekend, the wind will continue to drive the avalanche danger. Late Saturday afternoon and into Sunday it is looking like we'll have another extreme wind event. 

Regioni coperte