Avalanche forecast

Northwest Mountains

Crested Butte Avalanche Center
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Avalanche danger

Thu
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
3 · Considerable
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Out of date — this forecast expired 5 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

The avalanche danger is rising again and large natural avalanches are a threat today.  Fresh snowfall and strong winds are rapidly loading the same weak snowpack structure that produced extensive avalanche activity with the last storm.   On the northern half of the compass, avalanches can break several feet thick involving most of the season's snowpack.  Conditions are especially dangerous where intense wind loading is occurring onto high elevation, shady aspects.   Smaller slabs involving the drifted new snow will also be easy to trigger.  The safest riding today is either on low slope angles free from overhead hazards or on southerly aspects where the new snow is either sheltered from or being eroded by winds. 

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1.5–2.5

    Persistent slabs up to several feet thick will become easier to trigger and can fail naturally today.  The problem is on the north half of the compass, where the foundation to our thickening snowpack is weak and faceted.  In steep terrain, the distribution of these slabs is variable because of a widespread cycle that occurred last week.   Persistent avalanches can be remotely triggered from flat terrain below a steep slope, and avalanches might propagate much wider than you expect.  Collapsing snow and shooting cracks are warning signs telling you to stay away from steep terrain or move to a southerly aspect where the snowpack structure is lacking weak layers.  

    This widely propagating persistent slab ran naturally during last week's storm on Mt. Axtell. 

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–2

    New snow and strong winds will rapidly form sensitive drifts through the day.  Freshly forming slabs will be small at lower elevations, but could grow to large sizes in high terrain with efficient fetches and where snow totals are greater.  Stay off of steep terrain where you see snow actively blowing and loading the slope.  Winds will change direction from south to west through the day: expect slabs to form on a variety of aspects.  Anticipate unusual drifting patterns due to extreme wind gusts; drifts will be forming in crossloaded terrain features at low elevations and lower on slopes than normal.   Look for thicker drifts and cracking snow to identify the problem.  Wind slabs involving the fresh snow could step down and trigger a much larger persistent slab on shady aspects.  

    This is an example of several wind slabs that failed during the last storm.  

Avalanche Discussion

Snowfall is just firing up early this morning as the squall line approaches.  Expect a few hours of intense snowfall accompanied by unusually fierce winds, shifting from south to west.  Details in our weather tab.  The brief but rapid loading from this system is increasing the avalanche danger.   We are expecting an uptick in avalanche activity today, with the potential for natural avalanches.  Today's intense windloading is pointed directly at our most problematic aspects for persistent slabs - a big red flag.  Avoid traveling on or below windloaded north to east facing start zones today; that's where I expect to see the most natural activity.    Rapid snowfall rates will also add stress and increase the sensitivity of persistent slabs in wind-sheltered terrain.  Slopes on the northern half of the compass have been producing signs of instability all week.  That pattern won't change today.  You'll also have to contend with shallow storm instabilities developing around the compass as well.  In most areas, these instabilities will be confined to wind drifted terrain features where the new snow will quickly thicken into reactive wind slabs.  In areas that receive favored snowfall, you may also encounter shallow storm slabs developing on slopes that are sheltered from the wind (if such a place exists).    

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