Avalanche forecast

Northwest Mountains

Crested Butte Avalanche Center
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Avalanche danger

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

Nearly 3 feet of snow fell since Saturday night while southwesterly winds continuously drifted snow to leeward terrain features.  Natural avalanches remain possible on slopes with active wind loading today.  Avalanches on leeward slopes may break in the recently drifted snow, but there's a chance slides break deeper into the snowpack and grow to a destructive size.  You can find less hazardous conditions in wind sheltered areas free from overhead hazards, but with this much recent storm snow, you will need to skillfully assess the snowpack before entering steep terrain.

Avalanche problems

  • Persistent Slabs

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

    In the Northwest Mountains, avalanches can fail on buried weak layers on windloaded slopes, producing large to very large avalanches.  The most prominent and active weak layer is buried surface hoar several feet deep on the north half of the compass. There is also smaller potential for avalanches to break on faceted crust layers on some higher, southerly aspects, or depth hoar layers near the ground.  Persistent slab avalanches can be remotely triggered from low-angle terrain and break larger and wider than you might expect.  Avalanches breaking into old weak layers are unlikely on low elevation, southerly aspects.  Slope angles consistently less than 30 degrees away from runout zones are a reliable way to avoid the problem.  

  • Wind Slabs

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

    Nearly three feet of snowfall and strong winds are forming slabs, most commonly in wind-loaded terrain. Storm slabs are possible in wind-protected areas.  Slab avalanches breaking in the new and drifted snow have potential to step down and trigger larger persistent slabs.  Avoid traveling on windloaded slopes, where slabs will look and feel thicker.  In wind protected terrain, monitor for signs of instability such as cracking on small, steep terrain features to evaluate for new snow instabilities.  

Avalanche Discussion

Storm totals range from 1 to 3 feet with the Northwest Mountains accumulating the most; areas from Irwin to Schofield Pass in the Ruby Range snagged around 3 inches of Snow Water Equivalent!  Southwest winds continue to blow fast enough to transport snow above treeline and in some locations near treeline.  Natural avalanche activity could occur on slopes with additional wind loading or from cornice fall.  Poor visibility prevented observers from viewing much terrain however this observation documented a significant round of Persistent Slab avalanches on Whetstone.  

Expect to find dangerous conditions at all elevations in the Southeast Mountains forecast area.  Drifted terrain is the most dangerous as avalanche size is the greatest, but triggered avalanches in sheltered areas will be big enough to bury and injure you.  The recent avalanches on Whetstone suggest that portions of the forest area with a shallower overall snowpack have been pushed to the breaking point.  Avoid drifted terrain features and manage overhead hazards.  Choose conservative terrain and slope angles in sheltered areas highlighted by the Persistent Slab rose.  Low-elevation sunny slopes have less risk of Persistent Slab avalanches where the new storm snow rests on thicker crusts.  Carefully inspect the recent storm snow for instabilities before entering steeper terrain on sunny slopes below treeline.  If the sun comes out for an extended period, monitor snow surfaces for rapid warming.

Uncertainty increases in the Northwest Mountains regarding Persistent Slab avalanches.  Persistent Weak Layers are buried by feet of snow and have slowly become harder to impact by the weight of a person as slabs grow in thickness.  It may be difficult to trigger a deep failing avalanche in sheltered areas, but it remains possible on unsupported slopes, rocky terrain, convex rolls, or on slopes with shallower than average depths.  On wind drifted terrain, the concern for a deep failing avalanche increases; snowfall and loading placed an impressive burden on leeward terrain and some slopes likely teeter near their breaking point.  It would be wise to avoid drifted terrain features and limit your exposure time beneath as some avalanches could run further than you expect.

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