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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Out of date — this forecast expired 3 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

Dangerous avalanche conditions are forecasted to develop throughout the day as snowfall accumulates and strong southwest-to-west winds drift the new snow to leeward terrain features.  Expect to find sensitive slabs on drifted terrain features and the potential for cornices to fall which could trigger much larger avalanches.  Avoid wind-drifted slopes and seek out safer riding conditions in sheltered terrain at low elevations.  If you encounter 10 inches or more of new snow, evaluate how it is bonding to old surfaces and look for signs of instability like cracking to indicate worsening avalanche conditions in wind-protected terrain.

Avalanche problems

  • Storm Slabs

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

    Snowfall began early Tuesday morning and continues throughout Tuesday.  The most likely place to trigger an avalanche in the storm snow is on leeward slopes loaded by southwest and west winds.  As storm totals near a foot, avalanche problems in the storm snow may begin to develop on steep wind-sheltered slopes.  Cracking in the storm snow is a good indication that sheltered terrain is developing a Storm Slab avalanche problem.  Storm slabs commonly become most sensitive during periods of heavy snowfall.

    4/1: A wind slab triggered by a cornice fall.  Similar conditions will develop throughout the day on Tuesday.

  • Persistent Slabs

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

    Large, stubborn slabs several feet thick or more exist over faceted weak layers in the upper snowpack.  The most recent persistent slabs have required larger triggers such as the mass of a smaller avalanche running through the terrain or a cornice falling. The greatest number of avalanches have occurred on easterly-facing slopes where faceted crusts exist. Similar structures exist on west-facing terrain.  Recent warming on lower elevation and more southerly aspects has strengthened the upper snowpack with crusts, and triggering persistent slabs is less likely in that terrain.   Weak layers on north-facing terrain are less developed and have been less active.  

    Early warning signs for this avalanche problem are rare and feedback is infrequent. You can reduce your chance of triggering this avalanche problem by avoiding recently wind-loaded terrain and unusually shallow terrain.  Safer riding is where the snowpack is deep, wind-protected, and on slope angles less than 35 degrees, without steeper slopes above. 

    Very large persistent slab on the east face of Gothic Mountain. 3/31. This avalanche was likely triggered by a cornice falling onto the slope. 

Avalanche Discussion

Here we go again...another winter storm has arrived and will produce snowfall on Tuesday and probably into Wednesday.  Storm totals as of 5 am reach up to 5 inches for areas in the Ruby Range from Kebler Pass to Schofield Pass.  Strong southwest winds will shift to a more westerly direction during the day and form fresh Wind Slabs on leeward terrain.  The most dangerous conditions can be found on leeward terrain at upper elevations, particularly in the Northwest Mountains where the most snow is forecasted to fall.  Expect conditions to worsen throughout the day as more snow accumulates and the winds drift more and more snow to leeward terrain features.  Avoiding drifted terrain is a straightforward way to reduce your chances of triggering an avalanche.

There is uncertainty about how much snow will accumulate today.  The Northwest Mountains forecast zone is favored with this storm.  If snow totals near or exceed 10 inches, there is the potential for storm snow avalanche hazards to develop in sheltered terrain.  This could include Loose Dry avalanches and Storm Slab avalanches in the storm snow on steep, sheltered terrain.  Use small test slopes and look for cracking in the new snow to get a better understanding of the bonding between the new snow and old surfaces.  If you experience cracking then head to slopes that are 35 degrees or less.  Storm Slab problems often are most sensitive during periods of heavy snowfall.

There is a lingering chance of triggering an avalanche that breaks much deeper than the storm snow.  This potential is most likely on wind-drifted slopes at upper elevations, more common in the Southeast Mountains, and shallow/rocky terrain.  Several different faceted crusts exist in the snowpack in addition to well-developed Depth Hoar near the ground on northerly slopes with a shallow snowpack (less than 150cm or 5 feet).  The last two storm systems produced several deep and widely-propagating avalanches on well-drifted slopes at upper elevations.  It seems reasonable to anticipate similar types of avalanches to occur with this storm, particularly if cornices fail from another round of growth due to snowfall and wind.

The snowpack remains winter-like on most near/above treeline terrain.  An unusually snowy and cool winter season has left the snowpack seasonally confused.  Safer avalanche conditions will develop later this spring and an ample snowpack will linger for months to come.  Remains patient in your terrain selection as safer conditions are likely to develop in the next few weeks.

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