Avalanche forecast

Northwest Mountains

Crested Butte Avalanche Center
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Avalanche danger

Thu
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
1 · Low
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Highlights

The threat of triggering a persistent slab continues to slowly diminish with each passing day of dry weather. However, the consequences are still serious.  The most recent persistent slab activity was a  large remotely triggered avalanche near Irwin on Friday, and a smaller persistent slab triggered above Cement Creek on Sunday.  Careful snowpack assessments and terrain selection can help you avoid surprises.   Northerly winds continue to rake higher elevations.  Yesterday, a snowboarder had a near-miss with a wind slab on the south face of Teocalli Mtn.  Steer away from recently windloaded slopes.   

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely
    Size
    1.5–2.5

    On the northern half of the compass, there is a rare but dangerous chance you can trigger a hard slab avalanche that breaks up to several feet thick on weak faceted snow that was buried last month. Slabs can be triggered remotely from below or adjacent slopes.  Given the thickness and hardness of slabs, you are unlikely to get direct feedback, such as collapsing or cracking, until it's too late.  In the Northwest Mountains, slopes holding a shallower snowpack (less than about 2.5 meters deep) are most suspect.  This could be in steep, rocky terrain or in terrain that has variable depths due to wind erosion.   When in doubt, head for southerly aspects, lower consequence terrain, or slope angles in the lower 30-degree range and less. 

    This large persistent slab avalanche was remotely triggered on 3/18. 

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–1.5

    Strong north to northwest winds since Monday night have formed wind slabs below south and east-facing ridgelines and in cross-loaded terrain on all aspects.  A snowboarder had a near-miss with a wind slab yesterday on the south face of Teo.  Today's slabs could be a bit thicker, denser, and in a few slopes with large fetches, could be approaching D2 in size.  Although wind slabs may be more stubborn today,  they can break above you as you cross the margin of the slab.   Avoid crossing rounded, chalky-looking pillows of wind drifted snow in steep terrain, especially above terrain traps.  Wind slabs will feel thicker and look smoother than surrounding snow.   

    3/22: Shooting cracks on a wind drifted slope that nearly produced an avalanche on the south face of Teo.  

Avalanche Discussion

Northerly winds continued through the day yesterday and shifted to the northwest overnight, with steady wind speeds reaching 30 to 40 mph at the Cinnamon Mtn Wind Station.  Observers yesterday reported sensitive wind slabs up to a foot thick (Example A, Example B). The brunt of recent wind slab formation will be on high elevation south to east aspects, but you can also find cross-loaded slabs forming on other aspects.  Some of these drifts formed over near-surface facet layers and may not heal quickly.  Continue to steer around obvious drifts in consequential or heavily drifted terrain today: slabs could be hard and capable of taking you for a ride.  

Persistent slabs remain our primary concern given their dangerous sizes.  Slabs have potential to break several feet thick on weak layers buried in mid-February.  We are now more than 10 days out since our last notable loading event ended, and the likelihood of triggering a persistent slab is decreasing.  In the Northwest Mountains, we've lowered the likelihood of persistent slabs to "unlikely" today.  In general, the snowpack is deeper and weak layers are improving faster in the snow-favored zone.  There are always exceptions, especially in wind-affected alpine terrain. Given the potential size and variability near and above treeline, our travel advice remains the same consistent with Moderate danger.   Near the boundary of our two zones, and in the Southeast Mountains, collapses, shooting cracks, and unstable pit results have continued relentlessly since our weak layers were first buried.  Slabs are a bit thinner, weak layers are weaker, and human triggering remains possible on slopes that didn't already avalanche during the late February cycle.  

A significant warming trend starts tomorrow and is expected to bring rising wet avalanche danger into the weekend.  Early starts and early finishes are a good way to beat wet avalanche concerns.  For some objectives, that may mean getting to the trailhead before our forecast is published.  Plan accordingly, and expect the potential size and distribution of wet avalanches to increase through the next 5 days. Today's wet loose concerns should remain small and isolated.  

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