Avalanche forecast

Northwest Mountains

Crested Butte Avalanche Center
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Avalanche danger

Sun
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
3 · Considerable
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Highlights

Multiple days of snowfall and wind loading make for dangerous avalanche conditions.  Natural and remotely triggered avalanches on Friday illustrate the deadly threat.  Leeward terrain is the most dangerous and should be avoided.  Natural avalanches are possible on slopes with active loading or solar warming.  Sheltered terrain harbors an untrustworthy layer of surface hoar around 3 feet deep that has been responsible for recent avalanches and accidents.  Lower elevation sunny slopes are less likely to have the problematic weak layer but avalanches could fail in the recent storm.  Conservative slope angles are your best defense against a dangerous avalanche in sheltered areas.  You can always select terrain less than 30 degrees to manage the avalanche hazard and enjoy the fresh snow.

Avalanche problems

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1.5–2

    Snowfall from late Wednesday through Saturday morning coupled with consistent moderate to strong westerly winds have created an avalanche problem in the recent snow.  Settled storm depths exceed a foot in many places in the Northwest Mountains and much deeper on drifted terrain.  Recently drifted terrain is the most problematic with the recent storm snow, but even sheltered areas could produce avalanches.  An avalanche in the storm snow could "step down" and release a much larger avalanche on weak layers lower in the snowpack.  Avoid wind loaded terrain, understand that you can release a deeper avalanche where the Storm Slab problem overlaps with the Persistent Slab problem, and make careful assessments of the recent storm snow on low elevation sunny slopes. 

    An example of a large avalanche that failed on a wind-loaded terrain feature last week.

  • Persistent Slabs

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

    A new round of weak layers was buried on February 2nd. These weak layers consist of widespread surface hoar and facets on most east, north, and west-facing slopes, and along with some faceted crusts on higher elevation southerly aspects. Slabs about 3 feet thick (even thicker on wind-drifted slopes) above these weak layers can be triggered by skiers and riders. This avalanche problem can be remotely triggered from flat terrain or may propagate further than expected.  Shooting cracks or collapses are a clear sign of danger, but these obvious signs of instability will not always show themselves before an avalanche releases.  There is isolated potential to trigger older, larger slabs on weak layers deeper in the snowpack, most likely from shallow terrain features or step-down avalanches.  

    You can reliably avoid trouble by selecting terrain with slope angles less than 30 degrees that are free from overhead steep terrain.

     

    A remotely triggered avalanche from Friday.  This wind loaded northeast-facing slope on Axtel produced a dangerous avalanche on buried surface hoar and represents the dire consequences of releasing a Persistent Slab avalanche.

    Photo: Evan Ross

Avalanche Discussion

Avalanche conditions are dangerous in the Northwest and Southeast Mountains forecast zones.  Snowfall from Wednesday through Saturday morning has resulted in accumulations of a foot in most areas with some places in the Northwest Mountains even deeper.  Snow water equivalents range from about 1.6 inches to 1 inch.  Now factor in consistent westerly winds drifting all the new snow and you have a recipe for dangerous avalanche conditions.  Even with poor visibility on Friday, ample evidence was observed of the dangerous conditions like this remotely triggered avalanche on Axtel, these avalanches on Schuylkill Ridge, and natural activity immediately adjacent to town on Gibson Ridge.  Natural avalanche activity may continue today from drifting or solar warming due to clear skies.

There are two broad types of terrain you will want to avoid today to reduce the chances of triggering a dangerous avalanche.  First, avoid terrain with evidence of recent drifting.  These slopes will be commonly found at upper elevations where westerly winds transported snow, but could be found in isolated places at lower elevations.  Enough mass exists in just the storm snow to be problematic where drifted into thicker slabs.  Avalanches that break on weak layers below the recent storm snow could grow to very large sizes on some leeward slopes and be difficult to survive.

The second type of terrain to avoid is steep slopes highlighted by the Persistent Slab rose including sheltered areas.  There is some uncertainty about the impact of the recent snow on the buried surface hoar and the likelihood of releasing a deadly avalanche in sheltered locations.  The natural avalanches on Gibson Ridge point to increased sensitivity particularly for areas in the Southeast Mountains where the snowpack is generally shallower.  Surface hoar is a notoriously tricky layer and one we don't commonly deal with in the Crested Butte area.  The evidence and uncertainty point to making conservative terrain choices wherever you expect to encounter or find buried persistent weak layers.

Low elevation sunny slopes are the least likely place to encounter problematic surface hoar or facets, however, there is enough recent snow that you will need to make thoughtful decisions and skillful assessment of the snowpack before entering steeper terrain.

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