Avalanche forecast

Southeast Mountains

Crested Butte Avalanche Center
View on map

Avalanche danger

Thu
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
3 · Considerable
Open full map
Out of date — this forecast expired 3 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

More snowfall and wind-loading on Wednesday maintain dangerous conditions on drifted terrain; some avalanches could run naturally at upper elevations.  Avoid traveling on leeward terrain.  Human-triggered avalanches may become likely in sheltered terrain where you find more than about a foot of recent snow above weak layers in the upper snowpack.  There is a lingering threat of triggering an avalanche on deep weak layers where the snowpack is less than about 4 feet deep.  Low elevations southerly slopes offer lower risk options as fragile weak layers are unlikely to exist in the upper snowpack.

Avalanche problems

  • Persistent Slabs

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

    Last weekend's storm formed slabs 1 to 2 feet thick at mid and upper elevations 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
    Possible
    Size
    1–1.5

    An increase in southerly winds on Tuesday and Tuesday night drifted snow to the north half of the compass at upper elevations.  On Wednesday more snowfall and a shift in wind direction to the west in the afternoon will further load upper-elevation terrain.  This drifting may cause natural avalanches to break in the storm snow or persistent weak layers.  Some avalanches may just break in the drifted storm snow and run above crusts in the upper snowpack, however, it is difficult to know if a Wind Slab will step down into deeper weak layers.

    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

An Avalanche Watch has been issued in preparation for very dangerous (HIGH danger) conditions to develop by Thursday in the Northwest Mountains.  Storm totals could reach or exceed two feet on Thursday.  Lesser snow totals of around a foot are expected for areas closer to Crested Butte and the Southeast Mountains.

For Wednesday, the most dangerous terrain will certainly be on leeward slopes as the potential avalanche size is very large and some could run naturally due to snowfall and wind-loading.  Take a look at these avalanches from last weekend to get a feel for the deadly size potential and keep in mind these avalanches occurred last weekend.  Avalanches that fail today will increase in size as slabs continue to grow(Axtel, Bellview, Purple Peak).  Traveling on or immediately below drifted terrain is a deadly proposition today.

There have been a handful of human-triggered avalanches in sheltered terrain during and after this past weekend's storm.  You can see examples from the Anthracites, Purple Palace, and Axtel.  1 to 2 feet below the surface there is a nasty layer of surface hoar and near-surface facets.  Slabs have been relatively soft in sheltered terrain limiting propagation and sensitivity to human triggers, however, snowfall on Wednesday may dramatically increase sensitivity and drive propagation farther resulting in easy-to-trigger, large avalanches.  There is uncertainty about how much more snow is required to see an uptick in sensitivity but a reasonable expectation is for it to happen today.  Remain very skeptical of steep sheltered slopes highlighted by the Persistent Slab rose.

Some areas in the Southeast Mountains have much less snow resting above the problematic layer of surface hoar and facets.  With less snowfall forecasted and thinner, softer pre-existing slabs, expect to find reduced avalanche hazard in sheltered terrain in the Southeast Mountains compared to the Northwest Mountains.  This is a product of smaller-sized avalanches and less sensitive conditions in the upper snowpack.  Deeper weak layers exist at the bottom of the snowpack and can still be triggered by backcountry travelers where the snowpack is less than about 4 feet.  

In both forecast zones, lower elevation southerly slopes present lower risk options.  Warm temperatures before last weekend's storm built thick crusts insulating deeper weak layers and destroyed the problematic surface hoar found on other aspects.  You can always take the safest path and surf the fresh snow on slopes less than 30 degrees.

Regions covered