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

The Devil's work: slopes with the highest quality powder are where you are also most likely to trigger a dangerous avalanche that breaks on buried surface hoar 2 to 3 feet deep. This remotely triggered avalanche yesterday is a perfect example.  Crusty slopes are a much safer option, but you can still enjoy the soft snow on the shady side by managing slope angles and terrain consequences.  The most dangerous terrain is on the north half of the compass on slope angles steeper than about 35 degrees that funnel you into trees or gullies. Numerous wind slabs ran naturally on Sunday night; stay alert for lingering instabilities in drifted terrain at higher elevations.   

Lawinenprobleme

  • Persistent Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    2–3

    A new round of weak layers was buried on February 2nd. These weak layers consist of widespread surface hoar and facets on most east, north, and west-facing slopes, and along with some faceted crusts on higher elevation southerly aspects. Slabs about 2 to 3 feet thick over these weak layers have the potential to be triggered by skiers and riders. This avalanche problem can be remotely triggered from flat terrain, or may propagate further than expected.  Shooting cracks or collapses are a clear sign of danger, but these obvious signs of instability will not always show themselves before an avalanche releases.  There is isolated potential to trigger older, larger slabs on weak layers deeper in the snowpack, most likely from shallow terrain features or step-down avalanches.  

    You can reliably avoid trouble on terrain with slope angles less than 30 degrees that are free from overhead steep terrain. Lower elevation southerly aspects offer safer options for steep terrain.  

     

    2/19:  A remotely triggered persistent slab above the Slate River

  • Wind Slabs

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

    Strong northwesterly winds on Sunday night formed wind slabs onto south and east-facing slopes.  On some steep, leeward features, you can still trigger one of these slabs of drifted snow.  Be cautious of thicker, stiffer-feeling snow below ridgelines or in crossloaded gullies near and above treeline.   A triggered wind slab might step down and trigger a much larger persistent slab avalanche, like this recent avalanche on Mt. Owen. 

    A natural wind slab that ran on Sunday night on a southeast aspect of Hancock Peak. 

    (2/19/2024) Photo: Zach Guy

Avalanche Discussion

We documented more than a dozen D1-D2 wind slabs that ran during Sunday night's northwest wind event, and guides at Irwin found the problem was reactive to ski cuts on windloaded terrain.  This problem should heal fairly quickly after yesterday's warmup; the most concerning slopes for triggering a wind slab today are high-elevation south to east-facing slopes that didn't get crusted by yesterday's solar warming, and those instabilities should be more stubborn today.  Stay cautious on consequential slopes or terrain where larger fetches have created larger slabs.  

Our forecast team has been in an entrenchment mindset because of our buried surface hoar layer, which is keeping us off of some of our favorite steep riding terrain on the shadier side of the compass.  Since that layer was buried in early February, there has been a steady stream of persistent slab avalanche activity - almost daily. Check out the patterns of persistent avalanche activity in the past two weeks here, most of which likely failed on surface hoar.   Signs of instability have been diminishing in the Northwest Mountains where the layer is buried deeper, but the layer is still close enough to the surface that I don't put much faith in the more stubborn situation there, especially near and below treeline where the layer is largest.  After hearing about the remote-triggered avalanche above the Slate River yesterday, someone sent us a message saying "Crazy, I dug a couple quickies about there on Saturday and got no results in ECT".  The variability and erratic nature of surface hoar is why it has such a notorious reputation in the avalanche industry.  A former colleague and forecaster from NW Montana, in an area that gets surface hoar issues more often, sent me a message the other day, "Oof, I'd pick a facet crust over surface hoar any day. Surface hoar sucks."  One saving grace of surface hoar is that it doesn't grow underneath the canopy of evergreens. When slope angles and terrain consequences reach an unacceptable level for me, I'll duck into dense trees and stay away from clearings in the forest.  It's been a mindset shift this month that has me looking for creative or different routes in the mountains compared to my normal favorites.  

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