Avalanche forecast

Northwest Mountains

Crested Butte Avalanche Center
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Avalanche danger

Tue
Alpine
3 · Considerable
Treeline
2 · Moderate
Below
2 · Moderate
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Highlights

The avalanche danger will slowly rise through the day and is expected to reach Considerable sometime near or after sunset.   Skiers and riders have been finding the safest riding and best powder where the snowpack is deep and protected from the sun and wind on northerly aspects: watch for newly developing storm slabs in that type of terrain by later today.   Several large natural and triggered persistent slab avalanches have occurred on sunnier terrain with buried crusts (east, south, and westerly facing)  and on northerly aspects with thin and variable snow depths.  It was a tragic weekend in the Elk Mountains, with two fatal accidents since Friday.  Bring an acute sense of distrust to the backcountry today; this isn't our typical "spring snowpack."  

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2–3

    There are several faceted crusts in the upper snowpack that have produced dangerous avalanche activity this week, with slabs breaking several feet thick or more.  Most persistent slabs have failed on east and southeast aspects, though we suspect similar crust-related issues span to south and west aspects.   This problem has been particularly challenging because it has not provided feedback underfoot (like collapses) and stability tests are not giving reliable results.   You can reduce your risk by traveling to aspects where the problem hasn't been as active.  Choose simpler terrain when in doubt.  

     

    This very large persistent slab was triggered by a snowmobiler on 3/18.  

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–1.5

    Today's snowfall will start to develop thin storm slabs that will be sensitive to ski cuts.  Slabs will form later today and could become likely at higher elevations by sunset if we see the high end of snow and wind forecasts.  Monitor new storm totals and anticipate the new snow to bond poorly to current snow surfaces.  Today's storm slabs could cause trouble if they drag you into terrain traps such as gullies or trees.  Use small steep test slopes to assess how the new snow is behaving.  

    Example of the type of storm slabs we are expecting to develop by later today. 

Avalanche Discussion

We are in the early stages of a major loading event and the avalanche danger will start rising through the day.  The danger is expected to rise to Considerable overnight; the Northwest Mountains might get there before sunset if we get the high end of snow and wind forecasts.  The avalanche danger looks to peak on Wednesday during the culmination of heavy snowfall and intense wind loading.  New snow instabilities will start developing today.  They're most likely to form as slabs at higher elevations where snowfall accumulations are deepest and winds will be stiffening the new snow.   On northerly aspects, sluffs or slabs in the new snow will entrain more snow because the snow surface is currently loose and cohesionless.  Our current snow surface is weak and faceted, so instabilities should develop fairly quickly as soon as the new snow becomes thick enough to form a slab; somewhere in the 6" to 10" range.  

It's been a rough weekend for our backcountry community. Persistent slab issues have caught numerous groups by surprise this week in the Elk Mountains, and unfortunately, two of the accidents resulted in fatal outcomes. One accident was near Marble and the other near Aspen Highlands.  In the deeper zone, the issues appear to be tied to a near-crust faceted layer at the base of our two recent storms (March 10th interface), about 2 to 3 feet deep on average.  Our forecast team checked out the impressive crown on Mt. Baldy yesterday,  which was notably thicker due to extensive wind drifting.  This issue has been particularly challenging to forecast for because the layer was not obvious on the snow surface prior to its burial, so we don't have a clear map of its distribution.  Furthermore, it has provided very limited feedback in the way of collapses or unstable pit results.  Our best tool right now for plotting the problem is observing avalanche activity patterns, which have been most common on east-to-south aspects.  With significant loading over the next few days, we are in a stepping-back mindset, with more uncertainty on where and when this problem will act up again.  In our shallower zone, we are painting a broader distribution because we are also concerned about issues on northerly terrain where the snowpack is shallow and/or variable in depth.  Yesterday's accident in Maroon Bowl is a good example of that.  

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