Avalanche forecast

Northwest Mountains

Crested Butte Avalanche Center
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Avalanche danger

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Out of date — this forecast expired 6 years ago.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

Highlights

Heightened avalanche conditions exist at upper elevations, Primarily on wind-loaded slopes. Yesterday, backcountry riders human triggered a couple of small Wind Slab Avalanches, while westerly winds have continued to drift snow into small slabs on the lee sides of ridgelines and cross-loaded gullies. Normal caution is advised at lower elevations where the distribution of a potential avalanche problem is isolated in the terrain.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1

    At 12,000ft, northwesterly winds have been gusting into the 20's, while slowly building Wind Slabs on the lees sides of ridgelines and cross-loaded gullies. These slabs are expected to be generally small in size, up to about 15" thick, and located right near ridgelines vs further down the slope. These slabs will have the best distribution above treeline, and be considerably more isolated in their distribution at near treeline elevations.

    Tuesday 11/24, Small Wind Slab human triggered in the Upper Slate River Valley

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely
    Size
    1

    A patchy distribution of hard slabs on top of old, sugary snow exists on some high elevation, northerly-facing terrain features.  Although these persistent slabs are difficult to trigger, the resulting avalanche would break near the ground and have the power to drag you over rocks, stumps, or early season obstacles. Be cautious of terrain where you find thick, dense snow overlying a continuous layer of weak, faceted snow on the ground.

    High northerly aspect? ☑. Smooth ground cover? ☑. Weak snow on the ground? ☑. Windloaded slab? ☑. Here's what it looks like when you've found the ingredients for our current persistent slab problem.

Avalanche Discussion

Yesterdays thinking of continued snowfall leading to developing Storm Slabs didn't really pan out. Observers yesterday didn't find much, if any, reactive Storm Slabs in sheltered locations. Observers did however report drifting snow at upper elevations, and a couple of small Wind Slabs were human-triggered near ridgelines. These Wind Slabs are now driving today avalanche danger rating at upper elevations. The near treeline avalanche danger was dropped to LOW, not because you can't find the sweet spot and trigger a small Wind Slab or a deeper Persistent Slab, but because those avalanche problems are isolated in the terrain, leading to an unlikely outcome that you will find the sweet spot. Normal caution is advised at mid-elevations, with backcountry travelers continuing to keep an eye out for wind-loaded terrain, or sheltered locations with a slab of snow resting on faceted snow at the ground. 

This observation from the early season continues to be a great tool for understanding the potential distribution of today's Persistent Slab Avalanche Problem. That old October snow is now the weak layer on the ground. At lower elevations, the facets on the ground are moist and not producing test results. At upper elevations, those facets are present and weak, but the slabs above are hard, and it will be more difficult for a human to find the sweet spot to trigger an avalanche. Mid elevations, somewhere between 11,000 and 12,000ft, maybe the sweet spot for finding the right slab and weak layer combination. However, the distribution of where these two factors line up is still fairly isolated in the terrain. 

Mark your calendars! December 4th is CBAC's Virtual Avalanche Awareness Night.  A party and educational event, the likes of which you've never seen before.

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