Avalanche forecast

Northwest Mountains

Crested Butte Avalanche Center
View on map

Avalanche danger

Fri
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
2 · Moderate
Open full map
Out of date — this forecast expired 6 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

Several wind slab avalanches were observed yesterday and a wide propagating persistent slab avalanche was recently reported just next door in the Aspen area. Today it will be possible to trigger similar slab avalanches. The most concerning terrain features are located at near and above treeline elevations where winds have formed large, cohesive slabs above weak snow. These particular avalanches could be remotely triggered, propagate widely in the terrain, and become larger than expected. Obvious signs of instability have become less frequent, so don't necessarily expect feedback or a warning from the snowpack.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1

    Fresh Wind Slabs have formed at upper elevations and can be found on some slopes that are genurally easterly facing.  Expect these slabs to have formed immediately below ridgetops and have a smooth, pillowy appearance.  Shallow Wind Slabs may also be present on windward aspects in gullies or cross-loaded behind ribs.  Expect the Wind Slab avalanche problem to primarily exist along the western and northern edge of the Northwest Mountain forecast area.

    1/6: Human triggered wind slab on an above treeline south facing slope.

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2

    On or near steep terrain, you can trigger persistent slabs 2 to 4 feet thick that fail on weak snow near the ground.  Persistent slabs often surprise even the most experienced travelers: They give irregular feedback, they can propagate unusually wide distances, and they can be remotely triggered from below or adjacent to the slope.  To avoid this problem,  choose routes that stay off of, and out from underneath, steep terrain holding dense slabs over sugary weak layers.  Poor structure is most common on the slopes highlighted by the distribution rose above, on west to north to east and some southeast slopes.   Shooting cracks and collapses are clear warning signs to stay on slope angles less than about 30 degrees, although their absence isn't a guarantee of safety.   In the Northwest Mountains, slabs are generally thicker and denser: you are most likely to trigger them from shallow points on the slope such as rock bands, pungie trees, or where slabs taper in thickness from wind effects.  

    12/31: A large, remotely triggered persistent slab in Redwell Basin

Avalanche Discussion

The biggest change of recent, was a little bit of snow in the 2 to 7" range on Tuesday, with strong northwesterly winds continuing on Wednesday. For example, the 12,000ft weather station on Cinnamon Mountain had northwest winds averaging 30mph and gusting into the 40's yesterday. Nearby, backcountry skiers traveling above treeline on Mt Baldy were able to trigger, or remote trigger, a couple of fresh wind slab avalanches. These same avalanches will be more stubborn to triggering today but remain on the problem list for the Northwest Mountains. The Southeast Mountains saw similar winds but had less snow available for transport. 

The avalanche observation from Aspen, linked in the bottom line, is an interesting one to me. This avalanche failed around Wednesday Night, after only a few inches of new snow and similar winds to what we just experienced. Often enough, when weird things like this happen in the Aspen Area, they show up over here too. Or vice versa... Let's take the East Face of Gothic for example. That terrain has seen avalanche activity this winter, but nothing really gouging out the start zone. So could it be another small loading event away from releasing a wide propagating avalanche similar to the avalanches we are talking about in the Aspen Area? The loading period has mostly ended now that the winds have calmed down. Natural avalanche activity is unlikely. You are hopefully not thinking about skiing the East Face of Gothic. Yet for the advanced users, surprise events like this are interesting to keep track of and continue watching for trends. 

Moving the discussion down to lower elevations and more sheltered locations. Here, west, north, and easterly aspects continue to hold on to the persistent slab problem, but the snowpack has been slowly changing since the last major loading event back around December 28th. For areas in the Southeast Mountains, slabs have little by little began to lose strength due to faceting. As slabs facet and lose strength, they are less likely to propagate significant distances and the expected avalanche size is becoming smaller. Even though slabs are weakening, if you trigger an avalanche and are pushed into terrain traps like rocks, trees, or ditches then the consequences remain high. To see an example of weakening slabs in the Southeast Mountains take a look at this observation from Snodgrass. Sheltered terrain in the Northwest Mountains has received significantly more snow than the Southeast Mountains and slabs are denser and have yet to lose as much strength. The Persistent Slab problem, in sheltered terrain, for areas with deeper accumulations remains a more concerning problem due to the potential size even though triggering has slowly become less likely. Here is a recent video that also compares lower elevations with thinner slabs to higher elevations with thicker slabs. 

Regions covered