Lawinenlagebericht

Northwest Mountains

Crested Butte Avalanche Center
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Lawinengefahr

Sat
Hochgebirge
1 · Gering
Waldgrenze
1 · Gering
Unterhalb
1 · Gering
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Kernpunkte

The prolonged dry spell has caused avalanche concerns to become increasingly rare.   Previously wind-loaded slopes in very steep or rocky terrain are the most likely locations to find isolated exceptions to a generally stable snowpack.  A triggered avalanche will still be large and several feet thick.  Terrain with clean runouts free of trees, cliffs, or gullies will be more survivable if you find an isolated instability.    Conditions will change and the danger will rise with tomorrow's storm.  

Lawinenprobleme

  • Persistent Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Unlikely
    Größe
    1.5–2.5

    Slabs 1 to 4 feet thick exist over several persistent weak layers in the snowpack:  Weak facets and depth hoar near the ground and surface hoar layers in the upper snowpack. The problem has been most common on northerly and easterly facing slopes earlier this month, along with some wind-loaded westerly facing terrain.  Although many slopes are becoming dormant under our dry spell, there are a few terrain features where you may be able to trigger a surprisingly large avalanche involving most of the snowpack.  Persistent slabs can break wider than you expect, and they can be triggered from flat slopes adjacent to steeper terrain. You can reduce your risk by traveling on slopes where the problem isn't highlighted above, or by traveling on smaller terrain features without terrain traps.  You can avoid the problem on slopes consistently less than 30 degrees. 

    This large persistent slab was triggered by skiers descending the ridgeline on the Aspen side of the Elk Mountains last weekend, 12/17.  

Avalanche Discussion

Explosive testing of poor structures in both forecast zones continues to suggest that more slopes are becoming dormant due to our prolonged dry spell.  Dormant means that weak layers are not healed but have reached equilibrium under current conditions.  With additional loading, we expect our buried weak layers (such as the 12/7 surface hoar layer and 11/16 depth hoar layer) to become more reactive.  That could happen on some slopes tomorrow as we welcome our biggest storm in the past two weeks, and the avalanche danger is expected to rise accordingly.  Today, we still have concerns for isolated but surprisingly large instabilities; there may be a few bad apples out there waiting to spoil your day.  Practicing good travel habits, identifying potentially problematic terrain features, and choosing terrain with more forgiving consequences are techniques to defend against our low-likelihood problem.  

Yesterday, our forecast team triggered a long-running "facet sluff" in Climax Chutes.  This is symptomatic of our weakening snow surface on the north half of the compass.  Slopes that avalanched at the start of the month are relatively shallow and grow weaker with each day of dry weather.  Today, that means sluff management in the steepest terrain where you find loose, cohesionless snow.  Tomorrow, that means that storm snow will be falling on a weak interface and will have the potential to gain volume by entraining that old weak snow.    

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