Avalanche forecast

Mt Hood

Northwest Avalanche Center
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Avalanche danger

Wed
Alpine
3 · Considerable
Treeline
2 · Moderate
Below
2 · Moderate
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Highlights

Storm slab avalanches won't be as easy to trigger on Tuesday, but the potentially very large size should give you pause. Give the snowpack time to heal, sticking to open slopes less than 35 degrees and simple terrain where you limit your overhead exposure. At lower elevations warm up, pay attention to changes to the surface snow or rollerballs to avoid small wet loose avalanches on steep slopes. 

Forecast updated 0730 to moderate danger near treeline due to crust formation reducing the likelihood of human-triggered storm slabs slightly in this elevation band.

Avalanche problems

  • Loose Wet

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

    Freezing levels rising to 7000 ft will moisten previously dry snow and create the potential for wet avalanches. We expect these avalanches to be small, but could still bury you if they entrain some of the recent snow. Navigate to lower angle slopes if you see the precursors of wet avalanches such as rollerballs and wet or sticky snow.

    (12/20/2021) Rollerballs along Hwy 35 on a SE aspect near 4500ft. Photo: Andrew Kiefer

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2–3

    You can still trigger a very large and deadly avalanche on Tuesday. Rain and snow should finally taper off Monday evening, but the very heavy snowfall combined with warming created unstable snow layers that will take more time to heal. Slabs are thick (2-3 ft) and dense with "upside-down" layering and known mid-storm density interfaces. They sit above a glass-like bed surface (12/18) to run on. Widespread avalanche activity on a density change within the storm snow will be the most likely avalanches you can trigger. These may be small-large, breaking 6-12" deep. But if something rips down to the 12/18, these avalanches may be difficult to survive and we're most concerned about these avalanches at upper elevations where the bond to the crust may be poor. Avoid all open slopes steeper than 35 degrees until you gain confidence that these instabilities have healed in your terrain (through snowpack tests and small slope tests). Note that the heavy, dense snow formed a crust by Tuesday morning, significantly limiting the potential for human-triggered slabs as of Tuesday morning.

    (12/20/2021) A small skier triggered avalanche (D1) that broke 4-6in deep within new snow near Vista Ridge (6200ft, E aspect) Photo: Andrew Kiefer

Avalanche Discussion

A conveyor of heavy precipitation unloaded on Mt. Hood since temperatures turned colder Saturday night. Mt Hood forecast Andrew Kiefer ventured up the Mitchell Creek drainage on Monday. You can find his professional observation here. He found 30" of snow accumulated above the 0.25-0.5" thick 12/18 crust at 5500 ft. The snowfall ended warm and created an upside-down layering in the top 12" of the snowpack. Rainfall likely reduced snow accumulation significantly below 4500-5000 ft.

Red-flag signs of instability were widespread on Monday: They include a natural or snowplow-triggered small storm slab adjacent to highway 35 and a small skier-triggered storm slab on a test slope. Both avalanches were triggered on a density change about 6" down in the snowpack. Mt. Hood Meadows Pro Patrol also triggered widespread avalanches during control Monday morning.

Our focus remains above the 12/18 crust and we don't currently have any layers of concern deeper in the snowpack.

While the new snow has been filling in the terrain, you may still find brushy vegetation and open creeks at lower elevations.

Regions covered