Avalanche forecast

Northwest Mountains

Crested Butte Avalanche Center
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Avalanche danger

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

A large natural avalanche was observed on a drifted southwesterly face of Avery Peak near Gothic on Thursday.  Today, moderate westerly winds will transport snow to leeward slopes which will keep natural avalanches possible at upper elevations where wind-loading occurs.  Avalanches initiating in drifted start zones have the ability to run great distances and break wider than you expect.  Sheltered, low-elevation slopes have gone several days without loading and have shown few signs of instability recently, but if you were to find a shallow spot on a slope, you can still trigger a dangerous avalanche.

Avalanche problems

  • Persistent Slabs

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

    After more than a week of continued natural avalanche activity, Wednesday may have been the first day without a reported natural, but Thursday a scary, natural avalanche was reported off Avery Peak. Avalanches have been breaking 2 to 6+ feet thick, across entire start zones and producing destructive amounts of debris in their runouts. You can trigger avalanches while traveling on or below steep terrain. They can also release naturally from wind-loading or snowfall. The best way to reliably manage this problem is by traveling on lower angled slopes that don't connect to steeper terrain above. The likelihood of human triggering is decreasing towards possible while increasing winds will keep the threat of avalanches more likely at near and above treeline elevations due to wind-loading today. 

    A double overhead persistent slab avalanche in the NW Mountains

  • Wind Slabs

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

    An increase in westerly winds on Thursday and Friday will drift snow at upper elevations forming fresh surface slabs on leeward terrain features.  Expect newly formed Wind Slabs to be sensitive to the weight of a person or machine.  You are likely to find them below ridgetops and underneath cornices on leeward aspects.  They can also be found on cross-loaded in gullies and behind ribs on more windward aspects.

Avalanche Discussion

Increasing westerly winds yesterday and today are expected to transport snow at upper elevations onto leeward slopes.  A common theme over the past few weeks has been natural avalanche activity from wind-loading and it is reasonable to expect similar results today.  If winds in fact move snow around today, then I would not be surprised to see a couple more deep failing and broadly propagating avalanches.  This observation yesterday of a dangerous natural avalanche from Billy out near Gothic on Avery Peak helps to illustrate this point.  While your group travels through terrain today, in either the Northwest or Southeast Mountains, consider your overhead exposure to drifted features particularly if you observe active wind-loading.  The size of recent avalanches from upper elevation terrain may greatly exceed your expectations by breaking wide and running far.  It is prudent to give leeward slopes a very large buffer to cover the uncertainty.

Below treeline slopes, without recent drifting, are less concerning than large, drifted slopes, but can still produce dangerous avalanches.  For slopes below treeline in the Northwest Mountains, where slabs are very thick and dense, the chances of you triggering an avalanche have lessened but the potential size of avalanches has not changed and remains dangerously large.  Since thick slabs are helping to insulate the weight of a person from weak layers, avalanches are a bit harder to trigger, but finding a shallow spot on a slope, or trigger point, could result in a dangerous avalanche.  You should NOT anticipate getting signs of instability for much of the terrain in the Northwest Mountains to warn you of the potential danger.  Certainly, heed any signs of instability like cracking or collapsing if you do get feedback by differing to low angled terrain.  Remember that Persistent Slabs are often fickle beasts and allow multiple people to descend a slope before someone finds the 'wrong spot' and initiates failure.  Tracks on slope are not a good indicator of stability with the current avalanche conditions.

In the Southeast Mountains, where the snowpack is generally shallower below treeline, slabs are thinner which makes it easier for the weight of a person to impact weak layers.  Recent observations have suggested a mixed bag for experiencing signs of instability like collapsing.  This observation from yesterday near the Gothic Road above the East River pointed to sensitive avalanche conditions, but even with multiple collapses above steep slopes, no avalanches ran.  The snowpack in this area was generally less than 120 cm in depth with weak layers 2 feet or a bit more below the slab.  Slopes with a shallower snowpack, regardless of which forecast area you find it, should help clue you in to the increased sensitivity of triggering an avalanche.  Probing with a pole makes it very easy to feel the stark contrast of a strong slab over weak snow below.

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