Lawinenlagebericht

Northwest Mountains

Crested Butte Avalanche Center
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Lawinengefahr

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

The safest riding protected from severe windchill and sensitive wind slab problems is in wind-protected terrain at lower elevations.  In sheltered areas, manage for shallow instabilities - mostly sluffs - in very steep and consequential terrain.  In wind-affected terrain at higher elevations, you'll encounter thickening new slabs behind leeward features favored by today's increasing northwest winds.  Alpine terrain surrounding Kebler Pass will be most dangerous, where storm totals are close to a foot deep.    The rare threat remains for a larger and deeper persistent slab avalanche to be triggered at higher elevations in terrain with variable snow depths from previous wind effects.  

Lawinenprobleme

  • Wind Slabs

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

    Increased north to northwest winds are drifting the fresh snow into sensitive slabs in leeward and crossloaded terrain features near and above treeline.  Early instabilities yesterday highlight poor bonding at the storm interface, especially where it is faceted.  Although thin slabs may also exist in wind-sheltered areas that received more than 6" of new snow, slabs will be most common and more dangerous where winds are drifting the snow into thicker and denser deposits.  Look for blowing snow, deep drifts, and cracking under the new snow to identify the problem.  Choose smaller, lower angle slopes in wind-affected terrain, or move to wind-sheltered, low elevations to find safer riding.  

    This 8" slab failed on the weak snow at the storm interface yesterday.  Instabilities like this will be larger and more common today as winds redistribute the snow into thicker drifts.  

  • Persistent Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Unlikely
    Größe
    1.5–2

    Our region experienced a widespread avalanche cycle on November 26-27. On slopes that survived the cycle, slabs have now settled to 1 to 3 feet thick over faceted snow that formed earlier this winter. In the dry weather since, the snowpack structure is gaining strength,  and the problem has become isolated and difficult to trigger. Any surprises are most likely found on wind affected slopes with variable thickness facing west, north, east, or high southeast.   Slopes with consistently deep and uniform snowpacks or slopes that naturally avalanched last week offer lower-risk options for steep terrain on those aspects.  Move to smaller, less consequential terrain features when in doubt.  

    The last persistent slab triggered in the Northwest Mountains was this remotely triggered persistent slab on a west-facing slope above the Slate River on 11/28. This slope survived the natural cycle and had the necessary ingredients: a cohesive slab over weak, early-season snow.

Avalanche Discussion

Most weather stations show about 2" of new snow around the forecast zone, although observers yesterday reported locally deeper amounts of 8" to 12" from the Anthracites to the Southern Ruby Range.  These snow-favored areas will be most dangerous today and could rise to Considerable danger (Level 3) above treeline due to significantly more snow available for transport and entrainment.  Small naturals yesterday after only 6" of low-density snow highlight the fragile storm interface under the new snow. Expect sensitive instabilities again today, primarily on wind-drifted slopes, but potentially in a few sheltered areas that saw favored snowfall.    In parts of the forecast zone where snow accumulations were only a few inches, today's increasing winds won't have as much snow to work with, and wind slab issues will typically be small (D1-D1.5) and less common in the terrain (Possible).  We're showing a higher likelihood and larger potential size (a few slopes could produce up to D2) in the Northwest Mountains to address the parts of that forecast area with large storm totals.  Terrain features with broad and productive fetches from north to northwest winds will collect the thickest drifts.  

There is still isolated potential for a small windslab in the upper snowpack to step down or for a human trigger to find the sweet spot on the rare slopes harboring problematic persistent slab structure. Although the water weight from this storm is minimal (.1" to .3" of SWE), wind loading over the next 24 hours will add stress to the snowpack on heavily drifted terrain features. The persistent slab issue is most concerning in the Southeast Mountains where the shallower snowpack has produced a few avalanches breaking near the ground in the past week. Fortunately, the winds don't have much transportable snow in the shallow zone and are loading onto our southerly aspects, which generally have a stronger snowpack structure than their northerly counterparts.  Still, caution of leeward or crossloaded slopes where the persistent slab structure remains intact is prudent.  

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