Avalanche forecast

Northwest Mountains

Crested Butte Avalanche Center
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Avalanche danger

Fri
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
2 · Moderate
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Highlights

Avalanche hazards have improved with cooler temperatures and cloudy skies.  You can trigger a dangerous avalanche on terrain drifted by previous westerly winds.  Slopes with signs of recent drifting at mid and upper elevations are the most concerning.  A triggered avalanche in recently drifted snow could step down to deeper weak layers.  Safer terrain options exist in wind-sheltered areas, slopes with supportive melt/freeze crusts at the surface, and terrain less than 35 degrees.  Snowfall is forecasted to begin in the afternoon with strong southwest winds which may form shallow, fresh drifts later in the day.

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2–3

    Last week's storm formed slabs up to several feet thick over faceted weak layers.  Remote triggers and natural avalanches failing on these persistent weak layers have been gradually diminishing since widespread activity peaked last Wednesday.  The greatest number of avalanches have occurred on easterly-facing slopes where faceted crusts exist. Similar structures are also found on westerly-facing slopes. On northerly-facing slopes, these slabs formed over a layer of near-surface facets which should be bonding better now.  Slabs are larger at higher elevations due to previous wind transport.  In a few cases, avalanches have stepped down into older weak layers much deeper in the snowpack, causing destructive avalanches.  

    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 on wind-protected terrain less than 35 degrees, without steeper slopes above.

    This large persistent slab ran naturally on the afternoon of 3/28 on Schuylkill Ridge.

  • Wind Slabs

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

    Winds shifted from the northwest on Monday to the southwest Tuesday and Wednesday, forming drifts at higher elevations.   On Tuesday, we spotted over a dozen recent natural wind slabs and our forecast team intentionally triggered a couple of similar wind slabs up to 2 feet thick.  Drifted slabs are expected to be less reactive as a day or more has passed since formation, but they may still be sensitive to human triggers.   A triggered avalanche in recently drifted terrain could step down and trigger a much thicker and wider persistent slab.   You can identify the problem by looking or feeling for thick lenses of drifted snow below ridges and in gullies. You can avoid the problem by traveling where the snow is protected or eroded by winds.

    This 2-foot thick wind slab was remotely triggered near Hunter Hill on 3/28.  

Avalanche Discussion

Cloudy skies and cooler temperatures on Thursday have improved avalanche conditions.  The warming-related avalanche activity from Tuesday and Wednesday is not expected to be a concern today.  Melt/freeze crusts formed on sunny aspects and shoulder aspects at lower elevations which will reduce the likelihood of triggering an avalanche.  Slopes that have thinner crusts that break under skis or boards may not prevent the weight of a person from impacting weak layers in the upper snowpack and will make for poor riding conditions.  Below treeline terrain was removed from the 'most likely' distribution rose as there are fewer slopes of concern, but the avalanche size remains large if you were to release a slab avalanche. 

Previously drifted slopes near and above treeline are the most concerning particularly those that face northeast through southeast as slabs are the thickest from wind-loading.  Leeward slopes are capable of producing avalanches in the recently drifted snow and in some isolated places break much deeper producing a very large avalanche.  Recent examples of deeply breaking avalanches come from Whetstone Moutain on Monday during a previous storm and on Tuesday, two natural avalanches broke deeply around Crested Butte.  One avalanche released above Perry Creek in the Southeast Mountain Forecast Zone and another on the north side of Chair Mountain near Marble (outside the CBAC forecast area).  Take the time for thoughtful snowpack assessment if you enter steep terrain at upper elevations and be cautious of slopes with signs of recent loading.  Safer conditions can be found in wind-protected areas and by limiting slopes angles to 35 degrees or less.

A storm will begin impacting the area in the early afternoon.  Expect visibility to diminish in the PM and a fresh round of drifting to occur once the snowfall begins stacking up which may happen before sunset.  Expect the avalanche danger to increase on Friday as strong southwest-to-west winds drift the new snow onto leeward terrain features. 

Regions covered