Avalanche forecast

Northwest Mountains

Crested Butte Avalanche Center
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Avalanche danger

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Out of date — this forecast expired 6 years ago.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

Highlights

Human triggering a slab avalanche remains possible where you find a cohesive slab resting above weak old snow. The last slab avalanche was reported about a week ago on an upper elevation wind-loaded slope. These previously wind-loaded slopes, primarily at mid to upper elevations, still hold the largest potential avalanche size and heightened avalanche conditions. On some wind-sheltered steep slopes, observers have started reporting small loose dry avalanches or sluffs. If you find yourself lacking confidence or feeling uncertain about avalanche conditions, simply use the terrain to your advantage and consider lower angled slopes while further avoiding high consequence terrain features.

Avalanche problems

  • 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 35 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

Accumulated new snow for January remains in the single digits for our forecast area. The last measurable snow was about a week ago. In the last week, cold temperatures and a shallow snowpack have led to faceting and decaying slabs. This recent video highlights some of those changes. In recent days we are starting to see more reports of loose dry avalanches or in these cases, "facet sluffs", as the overall snowpack continues to weaken. This is basically the circle of life for the snowpack on a below-average snow year in our continental snowpack climate. During the dry periods, we watch the snowpack weaken and facet. With each loading period we see slabs build back over that week snow, a cycle of avalanche activity, then the whole thing starts to facet away again during the next dry period. 

The last loading event that was a week ago, largely impacted leeward terrain features at upper elevations due to northerly winds transporting new snow. The highest new snow accumulations during the period were in the Northwest Mountains with up to 7 inches accumulated near Irwin and Paradise Divide.  Below treeline slopes received very little snow from this event, only a few inches.  These factors make previously drifted near and above treeline features the most concerning and suspect.  Here are two observations from this loading event with a couple of skier-triggered avalanches and a large, natural avalanche.  Stability tests and signs of instability are showing improvement, but the evidence does not suggest that slabs are unreactive to the weight of a person or machine.  Predicting which slopes hang in the balance and which slopes have reached a temporary equilibrium is a challenging and complex decision.  A good way to look at decision making for traveling on upper elevation slopes, where you should be certain that slabs exist, is to think about consequences and less about likelihood.  Understanding the likelihood of triggering an avalanche on a given leeward slope remains a bit of a guessing game whereas judging the consequences of triggering an avalanche is a bit more straightforward.  If you are uncertain about the chances of triggering an avalanche on near and above treeline slopes then consider the consequences of being wrong.  Are there terrain traps like trees, cliffs, or gullies?  Is the slope large and and does it offer the potential for a long-running avalanche?  Your best tool for managing uncertainty is with thoughtful terrain selection that leaves room for error.

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