Avalanche forecast

Central Cascades

Central Oregon Avalanche Center
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Avalanche danger

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

On Monday Wind Slab avalanches will be possible on lee slopes where the wind has blown our newest snow to.  The size and danger from these avalanches will correspond directly to how much new snow we have received.  These avalanches may be touchier and propogate further due to surface hoar that was formed on Saturday night.  Similarly very shallow Storm Slab avalanches are possible in open glades below treeline because of this potential weak layer.

Avalanche problems

  • Wind Slabs

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

    Wind Slabs are formed when the wind blows snow across the terrain and this snow comes to rest on sheltered or lee slopes below ridgelines and behind crossloaded features.  Wind transported snow can be 3-5 times as deep as the amount of snow that has fallen from the sky.  The wind not only moves the snow; it also deforms the snow, breaking up the crystals so that they can pack tightly into a cohesive slab.

    During the period of snowfall from Sunday through Monday we will experience shifting winds.  On Sunday the wind was from the east, overnight it will be more southerly, and by Monday afternoon it will be from the southwest.  Due to this shift and variations across terrain features, wind slabs are possible on all aspects.  On Sunday morning there were observations from across the range of surface hoar.  If this surface hoar remained intact as the new snow fell, it could create a particularly weak layer for wind slabs to fail on.

  • Storm Slabs

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

    It is rare that I would forecast a Storm Slab avalanche problem with such modest amounts of new snow in the forecast.  However, due to a steady increase in temperature as the snow is falling and becasue of observations of surface hoar on Sunday morning, an "upside down" scenerio is likely.  Storm slabs will be very shallow but could propogate farther or be touchier than we would usually expect.  This is a good time to watch out for terrain traps where an otherwise shallow avalanche could have greater consequences.

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