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

An AVALANCHE WATCH is in effect. Dangerous avalanche conditions exist and natural avalanche activity is still possible, primarily on wind-loaded terrain today. Consider your overhead hazards, and travel cautiously near avalanche terrain. A more widespread natural avalanche cycle is expected to occur Saturday Night and through Sunday. Travel in or below avalanche terrain will not be recommended during that time. 

Avalanche problems

  • Persistent Slabs

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

    Snowfall and windloading this week are forming easily triggered and naturally releasing slabs over the fragile facets and faceted crusts that formed during our long drought.  Anticipate unusual and challenging behavior associated with these recently buried persistent weak layers, such as remote triggering and surprisingly wide propagation.  Even relatively thin slabs can grow to large sizes on the north half of the compass where they entrain the old, weak snow below (See video).  Shooting cracks and collapsing are clear warning signs of the problem.  There is isolated potential for slabs in the upper snowpack to step down into older weak layers near the ground, producing a deeper and larger avalanche.   You can reliably avoid today's problems by traveling on slope angles that are consistently less than 30 degrees in steepness without overhead hazards.  

    Several large avalanches on Mt. Baldy were remotely triggered from a long distance away on January 11.  

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Very Likely
    Size
    1–2

    Extreme winds overnight continued to load snow onto lee terrain features. Strong winds also made it down to some valley elevations and will have cross-loaded terrain features that don't often see wind-loading. Natural avalanche activity remains possible in wind-loaded terrain today. Avoid traveling on or below slopes with active wind-loading. 

Avalanche Discussion

Saturday is expected to be a relative lull, between peaks in avalanche activity. Over a hundred avalanches were recorded on Thursday, many more likely occurred last night. Winds are still elevated on Saturday with some accumulating snow continuing through the AM hours. Natural avalanches remain possible, primarily where this continued wind-loading is occurring today. As the snow available to transport decreases today, compared to last night, we will see a decrease in natural avalanche activity relative to the recent peaks. In wind-sheltered areas, the persistent slab avalanche problem will remain reactive and sensitive to triggering. However the variability of one slope to the next has increased as some slopes will have recent avalanches, and some slopes will just be waiting for the right trigger. Trying to outsmart the avalanche problem has many risks, and this would be one of them. 

This Sunday will be the first day this winter that we have HIGH avalanche danger at all elevations bans. Sunday is expected to be a very dangerous day in the backcountry and travel near or below avalanche terrain will not be recommended.

 

Below is a copy of the forecast discussion from yesterday. It has a good summary of the avalanche activity that occurred on Thursday. 

An extensive natural avalanche cycle occurred Thursday morning during the heavy snowfall event.  We documented over 145 avalanches that ran, including numerous remotely triggered avalanches (Ex. Mt. Baldy,  Ex. Kebler Pass).  The large slides on Baldy were triggered from up to half a mile away from the start zone!  While most of our documented avalanches were relatively small (D1-D1.5), larger terrain features and alpine slopes produced slides up to D2 in size.  We have yet to get good views of the higher elevation terrain in the deeper part of our zone, where we expect to see the largest slides, such as the Ruby Range and start zones of Axtell, Schuylkill Ridge, etc.    Also noteworthy: avalanches and signs of instability have been observed on all aspects around the compass.  Unlike some weak layers from earlier this winter, the January weak layer is widespread around the compass, consisting of very weak facets on the northern half of the compass, and faceted crusts on the southern half of the compass.  We've only excluded a couple of octants from the persistent slab distribution rose: south and southwest aspects below treeline in the Southeast Mountains because many of those slopes were too bare to have a continuous weak layer before this week's storm, and south aspects below treeline in the Northwest Mountains because our limited preliminary observations suggest the crusts are a bit stronger on low elevation, steep due south slopes.  Long story short, you should manage for the problem everywhere, unless you are on a slope that already avalanched or has sagebrush still poking out.  The biggest difference between the two zones is the average slab size: slabs are about twice as thick in the Northwest Mountains due to favored snowfall in the past week. Avalanches are equally sensitive to triggers in both zones.    

 

 

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