Avalanche forecast

Northwest Mountains

Crested Butte Avalanche Center
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Avalanche danger

Wed
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
3 · Considerable
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Highlights

Avalanche conditions are dangerous.  Up to 3 feet of snow fell recently with more forecasted today.  Southwesterly winds will blow hard enough to transport the new snow to leeward terrain.  You can trigger storm snow avalanches in sheltered and drifted terrain.  Storm snow avalanches have enough volume to bury you.  A small chance remains for an avalanche to break deeper into the snowpack where snow depths are variable and less than 6 feet.  You can reduce your chance of triggering a dangerous avalanche in the upper snowpack by avoiding leeward terrain and keeping slope angles less than 35 degrees. 

Avalanche problems

  • Storm Slabs

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

    Up to 3 feet of snow accumulated in the Northwest Mountains.  Settled Storm Slabs are 2 feet thick in sheltered areas and larger on drifted terrain features.  Prior to the storm, several observations mentioned surface hoar formation at a variety of elevations which may help create instability immediately beneath the new snow.  Look for cracking, utilize test slopes, and frequent hand tests to help understand the reactivity of the storm snow.  Areas with around 12 inches or more of settled storm snow will indicate the increased hazard and need for caution.  

    An example from a few days ago of an avalanche releasing in storm snow.  In this example, the avalanche failed in drifted storm snow but for today, expect similar storm snow problems to exist in sheltered areas as well.

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2–3.5

    Slabs ranging from 5 to 8+ feet thick have formed around much of the compass and at all elevations over faceted weak layers in the lower snowpack. These weak layers have adjusted to their current load and become more difficult to trigger. The most suspect areas to release this avalanche problem would be trigger points and areas where the snowpack thins to a below-average depth. Such as near rock bands, on some slopes that previously avalanched and have refilled, or where winds have formed variable snow depths. Persistent slab avalanches can propagate widely through the terrain, or be remotely triggered from low-angle slopes connected to steeper slopes. You can reduce your risk by traveling on slopes with a deep, uniform snowpack, and you can reliably avoid the problem by traveling on slope angles that are consistently less than 30 degrees and not connected to steeper terrain above.  

     

     

    1/4:  A destructive natural avalanche in Red Lady Bowl broke full-width last week.  This avalanche would be hard to survive.

Avalanche Discussion

The storminess continues with another round of moisture overnight and continued accumulations during daylight hours on Tuesday.  Total snowfall is nearly 3 feet for areas around Irwin to Schofield Pass with 2 inches of Snow Water Equivalent.  Closer to Crested Butte and east of town, snow totals are less than 2 feet with around 1 inch of Snow Water Equivalent.  Winds overnight from the southwest will slowly shift to the south changing the loading patterns throughout the day.  Some natural avalanche activity is possible today on drifted terrain.

In the Northwest Mountains, the primary concern lies with the storm snow and avalanches in the upper snowpack.  Soft slabs around 2 feet thick exist this morning and will grow throughout the day as mother nature continues to pile up the snow.  Use caution while managing the storm snow as it can become increasingly sensitive during loading periods.  Reports for yesterday indicated generally well-behaved storm snow but no real loading occurred due to very light snowfall.  Expect an increased chance for sensitive Storm Slabs today during periods of stronger snowfall and on drifted terrain features.  Yesterday one observer was able to find an area in the Anthracites with buried Surface Hoar which created sensitive avalanche conditions and produced easy propagating test results; it can be nearly impossible to predict where areas of buried Surface Hoar exist.  Exercise caution as the Storm Slab problem grows in sheltered terrain and drifter features today; conservative terrain choices are your best defense.

Smaller storm totals and a generally shallower snowpack in the Southeast Mountains forecast zone make for a different terrain management plan.  It is possible to trigger avalanches in the storm snow in places where you find 12 inches of new or wind-blown snow.  The trickier part of the equation is weak layers deeper in the snowpack becoming more sensitive due to the loading event.  As snowfall accumulates the balance continues to slowly move towards more dangerous conditions and an increased likelihood of deeper failing avalanches.  Drifted terrain is the most dangerous due to the increased burden from wind-loading and greater variation in snowpack depth.  If you are uncertain about avalanches failing deeper in the snowpack, simply defer to terrain 30 degrees or less and avoid exposing your group to overhead hazards. 

Regions covered