Avalanche forecast

Central Cascades

Central Oregon Avalanche Center
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Avalanche danger

Wed
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
1 · Low
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Out of date — this forecast expired 3 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

Triggering an avalanche on the persistent weak layers deep in our snowpack is unlikely, but would have catastrophic consequences.  A very large avalanche from the Diller Glacier on Middle Sister likely failed on one of these layers.  If you are riding near or above treeline on west, north, or east faces increase your margin of safety:  stay off of big steep slopes, shallow unsupported slopes, and steer clear of trigger points like convex rolls and rocks.

Avalanche problems

  • Deep Persistent Slabs

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

    Persistent weak layers from late December and early January are now deep enough in the snowpack that they are a Deep Persistent Slab.  Deep Persistent Slab avalanches are low likelihood and very high consequence events.  Throughout the terrain the contributing layers are burried 1-2m deep.  We can't expect feedback from Deep Slabs like collapses or whumphing, and often they become deep enough that digging profiles is impractical and compression tests do not work.  Startegies for dealing with Deep Slabs involve increasing your margin of safety.  I stear clear of big steep slopes, as well as shallow and unsupported slopes.  When you are traveling in avalanche terrain avoid trigger points like convexities and exposed rocks, and make sure your safe zones are well clear of the runout.

    The recent large avalanches on  Middle Sister were most likely Deep Persistent Slabs.

    The particular weak layers that we've been observing include surface hoar, near surface facets, and near crust facets.  All of these weak layers can be found at or just below the old snow interface (you'll know you're there when you are feeling multiple crusts).  These weak layers all formed during similar weather but the specific grain type is variable depending on elevation and aspect.

    (1/15/2024)

    2 large avalanches on Middle Sister (first observed on 1/14/2015)

    Photo submitted with public observation

    Photo: Benjamin Crosier

Avalanche Discussion

 Beginning Tuesday afternoon we will once again enter a period defined by new precipiation and stormy weather.  Notably, Wind Slab avalanches did not make their way onto the problem list for Tuesday.  This is because snowfall totals by late Tuesday afternoon will be minimal and I expect any instabilites attributed to the new snow to be very shallow.  Don't worry, I bet we'll have them in the Wednseday forecast!

Regions covered