Lawinenlagebericht

Northwest Mountains

Crested Butte Avalanche Center
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Lawinengefahr

Wed
Hochgebirge
2 · Mässig
Waldgrenze
2 · Mässig
Unterhalb
2 · Mässig
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Kernpunkte

You can trigger a deadly avalanche today particularly on slopes that face the north half of the compass.  Slopes with shallower or highly variable depths will increase the chances of you finding a trigger point and releasing a dangerous avalanche.  Safer terrain options exist on southerly slopes, wind-sheltered terrain, and places where you find a deep uniform snowpack.  Do not expect signs of instability like cracking or collapsing to alert you to a dangerous slope, but certainly heed those signs if you experience them.

Lawinenprobleme

  • Deep Persistent Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Unlikely
    Größe
    2.5–3.5

    It is possible to trigger a very large and destructive avalanche today in steep terrain or from flatter terrain where the snowpack connects to a start zone.  These widely propagating and long-running avalanches will break 6 to 10 feet thick or more on weak layers near the bottom of the snowpack.    Persistent slabs are most likely to be trigged on the northern half of the compass, where buried layers are most fragile.  Slabs have grown stubborn to human triggers because of how thick they are.  You are most likely to trigger a monster avalanche where slabs are thinner.  Thin areas are more common at higher elevations where the wind has redistributed snow into variable snow depths.   

    A recent deep persistent slab avalanche near Yule Pass.  

  • Wind Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    1–2

    Northerly winds on Saturday formed drifts in leeward terrain on the southeastern quadrant of the compass near and above treeline.  These drifts are getting more difficult to trigger, but they could be stiff enough to break above you.  Monday, alpine winds increased out of the southwest and may have formed small, sensitive drifts on the northeast quadrant of the compass at the highest elevations.   Look for thicker, denser lobes of drifted snow or blowing snow to identify the problem.  They'll be most common below alpine ridgelines or in cross-loaded terrain features.

    A small wind slab that ran naturally on the south face of Mt. Owen sometime around 1/2.

Avalanche Discussion

Evidence of extensive, and often destructive, avalanche activity from last Thursday, Friday, and Saturday continues to trickle in.  If you haven't looked through these images please do so in these observations and in the gallery below - a quick summary of activity with aerial images, closer images from Slate River and Poverty Gulch, and Brush Creek avalanche activity.  There was a tremendous number of avalanches big enough to bury, injure, and kill and many that were destructive in nature running long distances and overrunning lower-angled terrain.  The potential avalanche size remains dangerously large and deadly serious for the Deep Persistent Slab problem in the Northwest Mountains and Persistent Slab problem in the Southeast Mountains.

So why the MODERATE danger rating?  Slabs are generally thick and stiff from last week's prolonged stormy period and they act as a buffer to protect deeply buried weak layers from the weight of a person.  This simply means it is difficult for a person to impact weak layers and cause an avalanche however if you do, the consequences will be high (see images of massive natural avalanches above or better yet scroll through a few pages of recent observations here).  Much of the CBAC forecast area offers a lower likelihood of triggering with a very high consequence if you do.

Terrain with highly variable snow depths or shallow terrain represents the most likely places to trigger an avalanche particularly on the north half of the compass.  The snowpack at upper elevations has been redistributed by strong winds this past weekend helping to create variable depths.  Variable depths will leave some slopes with thin areas making it more likely for you to impact a weak layer and trigger a dangerous avalanche.  Additionally, some parts of the forecast area like low elevations near town and to the southeast did not receive as much snow which created thinner slabs that are more sensitive to the weight of a person.  This observation from Taylor Canyon, outside the CBAC forecast area, helps to illustrate the increased likelihood of triggering an avalanche where the snowpack is shallower and slabs are thinner.

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