Bollettino valanghe

Northwest Mountains

Crested Butte Avalanche Center
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Pericolo valanghe

Mon
Alta quota
4 · Forte
Limite del bosco
3 · Marcato
Sotto il limite
3 · Marcato
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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 storm really escalated in the past 24 hours and the Northwest Mountains are likely coming off of a large natural cycle this morning.  Avalanches breaking 2 feet thick or more will be very sensitive to human triggers, especially on west, north, and east facing slopes.  More naturals could run today. Some slopes have the potential to step down and produce much larger avalanches.   Expect remote triggering and unusual behavior with the surface hoar layer that was buried at the start of this storm.  We recommend avoiding avalanche terrain today.   

Problemi valanghivi

  • Storm Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Very Likely
    Dimensione
    1–2.5

    Up to two feet of new snow and wind drifting have formed easily triggered slabs that will be most sensitive on wind loaded slopes at higher elevations or on the north half of the compass where they are forming over fragile weak layers.  Storm slabs can be remotely triggered from below steep slopes because they formed on surface hoar.   Instabilities in the upper snowpack have the potential to step down and trigger larger and more dangerous persistent slabs where the problems overlap. Stay off and out from underneath slopes steeper than 30 degrees to avoid the problem.  

    2/4: A 12" storm slab triggered yesterday at the Anthracites.  Slabs are twice as thick today in some parts of the Northwest Mountains.  

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    2–3

    The recent storm will make old layers deeper in the snowpack more susceptible to human and natural triggers than earlier this week.   Persistent slabs up to several feet thick or more have the potential to fail widely or be remotely triggered from near or below steep slopes.  These dense old slabs may not give warning signs before releasing, but collapsing and cracking are sure signs of danger.   The problem is less concerning on wind sheltered southerly aspects where the recent warmup created thick surface crusts (see video).   The easiest and most reliable way to manage this problem is to ride on slopes consistently less than 30 degrees in steepness.  You are most likely to trigger a persistent slab where the snowpack is shallow or variable in depth, or if you trigger an avalanche in the new snow that gains enough mass to step down.  

    An example of a large persistent slab that ran earlier this week in the Elk Mountains.  The current loading pattern will make avalanches like these more likely to fail.  

Avalanche Discussion

Conditions vary significantly across the forecast zones due to significant differences in storm totals.  Read our weather forecast for details on which areas received the most snow and will have the most dangerous conditions today. 

Northwest Mountains: Tell Mother Nature it's underproducing, and it will laugh in your face.  The storm escalated in the Northwest Mountains yesterday and overnight, producing up to another 20" since yesterday morning's report.  In the favored Ruby Range, the danger rose to HIGH overnight and a large natural cycle likely occurred.   We are just coming off of the wind and snow loading period this morning, and conditions are just crossing back towards CONSIDERABLE.  Natural avalanches could continue from solar warming or light wind drifting today, and they'll be very sensitive to triggers at all elevations.  Yesterday, skiers and riders easily triggered fresh slabs 12" to 18" thick breaking on the facets and surface hoar layers that are widespread on west, north, and east aspects.  Those slabs are now up to 2 feet thick below treeline, and larger on wind-drifted slopes.  These new slabs will start behaving more erratically today, with wider propagation and longer remote trigger potential.  With storm totals as high as 3.2" of SWE, avalanches stepping down into older weak layers are a serious concern.  Though the peak of instability occurred before sunrise this morning, we recommend avoiding avalanche terrain today. It's going to be falling apart out there for skiers and riders.  

Southeast Mountains: Smaller storm totals (~6") make for a less dramatic change in conditions.  The biggest driver is the constant wind drifting over the past 36 hours. The shallow zone always produces with productive wind transport, so I expect we'll see natural activity as well, just not as widespread and more confined to wind drifted features.  The persistent slab problem has also shown a pattern of waking up every time we see snow transport this winter; there are more slopes in our shallow zone with a shallower and weaker snowpack that will become reactive to the additional loading from the wind drifting.  Observations from below treeline suggest there wasn't quite enough snow to create storm slab problem yet, but monitor for cracking or collapses to look for outlier conditions.  

Events: Our next Fireside Chat is TODAY at 6 p.m. at High Alpine Brewing Company in Gunnison. A local snowmobiler will talk about his experience with an avalanche burial and rescue while snowmobiling last year.

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