Avalanche forecast

Northwest Mountains

Crested Butte Avalanche Center
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Avalanche danger

Sun
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
3 · Considerable
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Highlights

Snowfall overnight and today will bring 8 to 16 inches to the Northwest Mountains and create dangerous avalanche conditions as early as mid-morning.  The most concerning terrain faces west to north to east where buried weak layers exist around 2 - 4 feet below the surface; avalanches could break into old snow creating large avalanches.  On sunny slopes, the new snow is falling on thick crusts and avalanche concerns are anticipated to remain in the storm snow.  Collapsing and cracking are clear indications that buried weak layers are primed to avalanche.  Use caution around all steep terrain particularly drifted terrain, and choose lower-angled slopes where you find 10 inches or more of new snow.

Avalanche problems

  • Persistent Slabs

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

    You can trigger slabs 2 to 4 feet thick that fail on a layer of faceted snow buried below the storm interface (the February "sand box" weak layer).  This problem is can be found on west through north through east slopes.  The new snow will likely awaken this weak layer and create dangerous avalanche conditions.  Slopes that avalanched a week ago remain highly suspect (see this observation for 'repeat offender' potential).  Persistent Slab avalanches can be triggered remotely from below or adjacent slopes.  Collapsing and cracking are clear signs that this weak layer has been overloaded and primed to avalanche.  Use caution on slopes facing the north half of the compass.  

    This photo from Cement Creek illustrates how persistent slabs can be triggered from a long ways away from the start zone.  The avalanche was remotely triggered by a snowmobile on 2/27.

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–2

    Avalanche could break at the storm interface or within the storm snow.  This problem will be more commonly found on sunny slopes where the storm snow fell on melt/freeze crusts.  Look for cracking in the storm snow and find small test slopes to identify instabilities within the storm snow.  You can also perform hasty hand pits to check the bonding between the storm snow and old crusts. 8 inches of storm snow is a good threshold for raising your concern for triggering an avalanche in the storm snow.

    An example of an avalanche breaking at the bottom of storm snow below treeline on a steep convexity.  

Avalanche Discussion

A storm system is increasing the avalanche hazard and creating dangerous conditions.  Storm totals in the Northwest Mountains range from 6 to 12 inches as of 6 am and 3 to 7 inches in the Southeast Mountains.  Mother nature will add to these totals with another 3 to 6 inches during the day.  The snowfall is favoring areas in the Northwest Mountains and you should expect to find the most dangerous conditions there.  Areas in the Southeast Mountains that border the Northwest Mountains may become dangerous as well.

The new snow is creating the greatest concern on slopes facing the north half of the compass.  On shady slopes, the concern is for avalanches to break 2 to 4 feet deep on the "February drought" layer.  The "drought" facet layer was initially buried over a week ago and produced a widespread avalanche cycle during last weeks storm and resulted in many human-triggered avalanches.  Unfortunately, this layer was thick enough that it was not destroyed or removed by natural avalanche activity and remains a worrisome problem even on slopes that avalanche during the last storm.  If you are venturing into terrain with any northerly component dial back your slope angles and anticipate human-triggered avalanches to be likely with natural avalanches possible during periods of heavy snowfall.  Avalanches breaking on the February facet layer will be big enough to bury you in many locations.

On southerly-facing terrain, the new snow is falling on melt/freeze crusts and avalanches are expected to remain in the storm snow.  Expect drifted, sunny terrain features to be more dangerous as southwest to west winds transport the new snow into thicker slabs on leeward terrain.  Take the time to inspect the bonding between the storm snow and the old crust before you commit to avalanche terrain on sunny slopes.

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