Avalanche forecast

Northwest Mountains

Crested Butte Avalanche Center
View on map

Avalanche danger

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Out of date — this forecast expired 3 years ago.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

Highlights

A slow drop in avalanche hazard continues under stable weather conditions, however, a small chance lingers for you to trigger a large and dangerous avalanche.  Upper-elevation slopes facing west to north to east with previous drifting are the most likely locations to find trouble.  Signs of instability are less common so don't necessarily expect the snowpack to warn you.  You can find safer options at lower elevations.  You can further reduce your risk by picking slopes without terrain traps so that the consequences of an avalanche are less severe.

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1.5–2.5

    Slabs 1 to 4 feet thick have formed over several persistent weak layers in the snowpack:  Weak facets and depth hoar near the ground and surface hoar layers in the upper snowpack. The problem has been most common on northerly and easterly facing slopes this month, and has also recently been active on westerly facing terrain. Persistent slabs have generally become difficult to trigger and signs of instability are infrequent, but if you cross the wrong slope or the wrong spot on a slope, a single collapse can result in a surprisingly large avalanche involving most of the snowpack.  Persistent slabs could break wider than you expect, and they can be triggered from flat slopes connected to steeper terrain above you. You can reduce your risk by traveling on slopes where the problem isn't highlighted above, or by traveling on small terrain features without terrain traps.  You can avoid the problem on slopes consistently less than 30 degrees. 

    A very large natural avalanche on an east-facing slope of Treasury Mtn that likely ran on 12/10

Avalanche Discussion

The last notable loading event occurred Thursday night (12/14) and into Friday (12/15) with a northerly wind event that drifted snow on open terrain, largely at upper elevations.  This event produced a few natural and human-triggered avalanches.  Since then, the weather has been mild with light winds resulting in a slow reduction of avalanche hazard.  Even though avalanche hazards are slowly improving over time, poor snowpack structure is common on the north half of the compass.  As time increases from the last loading event, the likelihood of you triggering an avalanche slowly declines, but the potential size remains large and dangerous.

A reasonable way to manage the lower probability of triggering yet higher consequence scenario is to place greater importance on the consequence side of the equation.  Pick terrain that allows for a greater margin of error such as smaller slopes, terrain without terrain traps, and avoid places with signs of previous wind loading.  "Lemon" slopes and spots on slopes exist across the landscape where you can trigger a large and dangerous avalanche; use the terrain to reduce the severity of an avalanche if you are unlucky enough to find one of those slopes.

The terrain below the treeline presents safer options as the last significant loading event was back around December 7th and 8th.  You can find a poor structure on low-elevation northerly slopes, particularly above about 10,500 feet or isolated drifted terrain features.  Boot penetration could be a good way to identify the isolated suspect slopes below treeline; if you experience a supportive-to-boots snowpack on steep northerly terrain features then you might have found one of these isolated places where a slab avalanche is possible below treeline.

 

Regions covered