Avalanche forecast

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Northwest Avalanche Center
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Avalanche danger

Tue
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
2 · Moderate
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Highlights

Shallow wind slabs that formed over the weekend will be slow to heal thanks to frigid temperatures.  Avoid steep slopes below cliff bands where spindrifts will shed new low-density snow.  Steer around slopes below ridgelines with smooth pillowy drifts.  At lower elevations and in the eastern foothills, red flag indicators like whumpfs, rolling collapses, and recent avalanches tell us that a persistent slab avalanche can be triggered on open slopes greater than 30 degrees in terrain with enough snow cover.  

Avalanche problems

  • Wind Slabs

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

    Several inches of low-density fluff accumulated through Sunday afternoon.  Even before the new snow was done, one small wind slab was intentionally skier-triggered below a ridgeline Saturday.  It's likely that you'll encounter shallow wind slabs that were built over the weekend directly below ridgelines and steep slopes below cliff bands.  With temperatures closer to 0F than to the freezing mark for the next several days, instability in the upper snowpack will be slow to heal.  Continue to look for recent wind loading patterns as you travel higher in elevation and into more exposed terrain.  Blowing snow, sharp cornices, and drifts behind rocks/trees will help you anticipate wind-loaded aspects. Steer around smooth pillow-like drifts and stick to lower angled or less wind-affected terrain. 

    (12/17/2022)

    Blowing snow on the higher peaks Saturday (12/17) showed some signs of wind transported snow. 

    Photo: Katie Warren

  • Persistent Slabs

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

    This problem seems to live in the lower elevations primarily near and east of Mazama.  Often this isn’t the terrain we associate with large avalanches. However, several observations of cracking and collapsing in these eastern mountain environs culminated in a large 500 ft wide avalanche this past week. If you see shooting cracks, feel sudden collapses, or hear whumpfs from the snowpack avoid traveling on or under any nearby steep slopes. In these locations, you may find a layer of weak sugary facets in the lower portion of the snowpack, often under 1 or 2 crusts.

    (12/14/2022)

    Large avalanche crown running across the top of an east-facing slope in Finley Canyon, southeast of Twisp.

    Photo: Public Obs

Avalanche Discussion

3-5" of snow accumulated Saturday night and Sunday with very cold temperatures and moderate westerly ridgeline winds.  Professionals in the Silverstar area on Sunday found no wind effect up to 6400' and experienced frequent collapses at lower elevations.  Very small pockets released on buried weak layers below 5000' on unsupported terrain features (see photos). 

Reports from avalanche professionals this week noted surface hoar in sheltered terrain prior to the storm. In exposed areas, the wind knocked these weak grains over. A thin breakable sun crust was observed on steep southerly slopes. We will want to track these older surfaces buried 12/18 as the storm pattern picks up next week. 

In the WA Pass areas, two other notable layers remain in the snowpack. Buried SH (12/8), often found about 8-12 in below the surface, continues to linger but has not been an issue so far. While you may still find the mid-November facets (and crusts) in the lower portion of the snowpack, professionals have not reported any recent significant snowpack test results.

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