Avalanche forecast

Southeast Mountains

Crested Butte Avalanche Center
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Avalanche danger

Fri
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
3 · Considerable
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Highlights

You will encounter dangerous avalanche conditions on leeward terrain features due to snowfall and strong westerly winds.  Expect to easily trigger avalanches on drifted terrain with the potential for avalanches to break in the upper snowpack or on deeper weak layers.  You will find less avalanche risk below treeline in wind-sheltered terrain, but soft slabs around 12 inches thick rest above weak layers that may be sensitive to the weight of a person.  Some chance remains for you to trigger a deeper avalanche where the snowpack is less than about 4 feet.  You can find safer conditions on low-elevation, wind-protected southerly slopes.

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–2.5

    Recent snowfall has formed slabs 1 to 3 feet thick over widespread weak layers of surface hoar and facets on most east, north, and west-facing slopes, and potentially faceted crusts on high-elevation southerly aspects.  Slabs will increase in size with snowfall and drifting on Wednesday.  These slabs have been sensitive to human triggers, evidenced by recent triggered and natural avalanches, and likely become more sensitive as more snow accumulates today. They can be remotely triggered from flat terrain, or propagate widely across terrain features.  Shooting cracks or collapses are a clear sign of danger.  This problem is generally D1 to D2 in size.

    There are old faceted weak layers near the ground that are more stubborn to human triggers. These dense old slabs may not give warning signs before they release; they are most commonly triggered from terrain features with shallow or variable snowpacks, or if avalanches in the upper snowpack gain enough mass to step down.  This problem is generally up to D2.5 in size.  

    The most reliable strategy for avoiding these issues is by riding on slope angles consistently less than about 30 degrees.  Mid to low-elevation southerly slopes are less problematic.   

    2/4: This avalanche on Mt. Axtell exemplifies our newest generation of persistent slabs (recent storm snow breaking on facets or surface hoar), which then stepped down and triggered older hard slabs deeper in the snowpack on old weak layers near the ground.  

  • Wind Slabs

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

     On Wednesday and Thursday snowfall and strong westerly winds loaded leeward terrain features.  This drifting may cause natural avalanches to break in the storm snow or persistent weak layers deeper in the snowpack.  Some avalanches may break in the drifted storm snow and run in the upper snowpack, however, it is difficult to know if a Wind Slab will step down into deeper weak layers.  Simply avoid all drifted terrain to greatly reduce your risk of triggering an avalanche. 

    2/5: A recent Wind Slab on the east side of Star Pass.  You could trigger a similar avalanche today as more snow and wind load alpine slopes.  An avalanche in the upper snowpack could step down to deeper weak layers and release a much larger avalanche.

    Photo: Eric Murrow

Avalanche Discussion

Northwest Mountains:  An Avalanche Warning is in place for very dangerous avalanche conditions.  Storm totals range from about 10 to 14 inches of relatively dense snow (storm totals are likely deeper at upper elevations and there is a few-hour lag in weather stations reporting this morning).  Snow Water Equivalents have exceeded 1" early this morning with more snow forecasted during the day.  Strong westerly winds have been transporting snow to leeward terrain on the east half of the compass.  This round of snowfall is adding to existing slabs from this past weekend's storm.  There is a reasonable degree of confidence that large to very large avalanches are running naturally on drifted terrain features; some of these avalanches could be failing on deep weak layers near the bottom of the snowpack.  We got a small preview of the potential this past weekend with deep-breaking avalanches on Axtel, Bellview, and Mount Emmons.  When visibility improves after this stormy period ends, I expect to see that more very large avalanches have failed. 

In Sheltered areas, a widespread weak layer exists comprised of surface hoar and facets.  You can check out this video from a week ago describing it before it was buried.  This layer is now buried 2+ feet deep across the Northwest Mountains.  There was relatively little natural avalanche activity after this weekend's storm in wind-protected places, but there has been a handful of human-triggered avalanches on this interface this past week.  Yesterday, observers reported easy-to-trigger avalanches about two feet deep where the slab rests over persistent weak layers.  One backcountry traveler in the Anthracites triggered a slide and was carried into a tree resulting in minor injuries.  There is some uncertainty about a widespread natural avalanche cycle in sheltered terrain, HOWEVER, human-triggered avalanches are very likely with many avalanches big enough to bury and injure you.  The hazard is further increased by very large natural avalanches running from alpine terrain into below treeline areas.

Avoiding avalanche terrain in the Northwest Mountains is the simple travel advice.  Keep tabs of overhead hazards as some natural avalanches may run much longer than you expect and remotely triggered avalanches are on the menu.

Southeast Mountains: With less snowfall in the Southeast Mountains (storm totals might max out around 10 inches with today's additional snow), avalanche hazards are less dire.  You can still encounter dangerous avalanche conditions on drifted slopes.  Strong westerly winds have loaded the east half of the compass and natural avalanche activity is expected.  Avoid leeward terrain features to greatly reduce your risk.  In sheltered areas, the same widespread weak layer exists on west through north through east aspects, but slabs are generally soft and only about a foot thick.  You could still trigger an avalanche where you encounter 12 inches or more of recent snow above weak layers in the upper snowpack.  Look for cracking or collapsing to clue you into unstable conditions in the upper snowpack at below treeline elevations.  There is some risk of triggering a deeper avalanche in sheltered areas where the snowpack is generally less than 4 feet deep for aspects highlighted by the Persistent Slab Rose.   Lower elevation, wind-protected sunny slopes offer lower risk options as weak layers are less common in the upper snowpack, and deep weak layers are insulated by thick crusts that formed a week ago.

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