Avalanche forecast

Northwest Mountains

Crested Butte Avalanche Center
View on map

Avalanche danger

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Out of date — this forecast expired 5 years ago.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

Highlights

An Avalanche Watch is in effect with very dangerous conditions expected to develop tomorrow.  Mega storm totals since Christmas Eve are stressing buried weak layers near the bottom of the snowpack. Very large and destructive natural avalanches are possible today, and you can easily trigger them from on or below steep terrain.  Unusual avalanches should be expected, such as this large natural that ran yesterday on Mt. Crested Butte.   We recommend a conservative mindset today: low-angle terrain (less than 30 degrees) with minimal exposure to overhead hazards.

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    2.5–4

    Large and destructive avalanches are sensitive to human triggers and have the potential to fail naturally today.  These widely propagating and long running avalanches will break 5 to 8 feet thick or more on weak layers near the bottom of the snowpack.    Persistent slabs are most common on northerly and easterly aspects, where these buried weak layers are most fragile and slabs are more widespread. The distribution rose also includes south to west aspects where there may be potential for crusts near the bottom of the snowpack to collapse. Given how thick these slabs are, you may not observe any obvious signs of instability. For example, two large avalanches were human triggered on Mt Emmons on Saturday; neither group reported any warning signs, such as collapses or shooting cracks.  

    A persistent slab triggered from a low angle ridgeline on Red Lady Glades. The slide broke 3 to 4 feet deep and ran far.

  • Storm Slabs

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

    2 to 3 feet of fresh snow and gusty southwest winds have created instabilities in the upper snowpack, mostly in wind drifted terrain.   Slabs will be most sensitive near and above treeline where winds have stiffened or drifted the snow into more cohesive or thicker slabs.  New snow instabilities are easier to recognize: you are likely to see cracking in the snow or get feedback on steep terrain.  However, any moving snow in the upper snowpack could step down and trigger a larger persistent slab.  You can avoid triggering storm slabs by riding on slopes less than 30 degrees.  

    An example of an avalanche earlier this season, that propagated widely below a wind-loaded ridgeline.  

Avalanche Discussion

This video gives a brief snowpack history and context as to why avalanche conditions are so dangerous right now.     The snowpack has tripled in size since Christmas Eve.  Schofield Pass has picked up a whopping 10" of snow water equivalent (more than 10 feet of snow) with this storm, and CBMR has tallied 68" of accumulating snow since the storm started on December 23rd.  This is a significant and continuous loading event onto several persistent weak layers.  We have had limited visibility and limited observations over the past few days.   The one avalanche observation from yesterday confirms that conditions are far from ordinary: A large avalanche released in a heavily timbered path on the southern side of Mt. Crested Butte, a path which rarely sees such action.  There has been an unusual amount of surprises and near misses amongst avalanche safety operations around the state with this storm.  That reflects the especially challenging conditions of this cycle.  Slabs are denser and thicker than what we typically see in December, meaning that they can break wider and have more mass to run further.    It is a time to exercise more caution than usual.  Our forecast staff is in an entrenchment mindset until this storm clears after New Years.  

The downtrend in today's danger is a mere reflection of the decreasing likelihood of naturals today, given a brief lull in heavy snowfall rates.  Naturals are still possible today, either from wind drifting or snowfall, and anything that runs has potential to be very large and destructive.  If you see heavy snowfall rates or strong wind loading, expect a higher danger.  The sensitivity of human triggering is also decreasing due to the enormous slab sizes.  This isn't something I would gamble with today; slabs are still very stressed.  Tomorrow, we expect natural activity to increase through the day and surge overnight with a very impressive storm that culminates this prolonged loading period. Our weather tab has details on this system.  An Avalanche Watch is in effect today, and will likely upgrade to a Warning tomorrow morning.  The avalanche danger will rise to HIGH tomorrow and could rise towards EXTREME on Thursday night.  Tomorrow's forecast shift will iron out those details as the storm gets underway.  

 

 

 

Regions covered