Lawinenlagebericht

Central Cascades

Central Oregon Avalanche Center
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Lawinengefahr

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

The surface snow conditions vary more widely than we are used to in the OR Cascades.  This can be attributed to both: the recent inversion where lower elevation terrain has remained colder than higher terrain, and to a slope's position in the range with features near the crest having received freezing rain on Sunday morning.  Wind Slab avalanches will remain possible on north, east, and south slopes at upper elevations and where the snow has remained dry.  Persistent weak layers exist deep in our snowpack, and while triggering an avalanche on these layers is unlikely, the resulting avalanche would be very large.

Lawinenprobleme

  • Wind Slabs

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

    Our most recent storm created Wind Slabs and Wind Slab avalanches.  These Wind Slabs can take a couple of days to stabilize and it will remain possible to trigger a Wind Slab avalanche on Monday.  Wind Slabs are most likely on steep north, east and south slopes at upper elevations where the wind has blown the snow.  They are much more likely on features that avoided Sunday morning's freezing rain.

  • Persistent Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Unlikely
    Größe
    2–3

    Before all of our recent storm snow, our snowpack was shallow and we had some very cold nights.  This led to the development of persistent weak layers (facets and surface hoar).  The types of weak layers vary a bit across different aspects and elevations, but in all cases they are are located near the old snow surface.  This is easy to find in a profile or by probing because you feel old crusts in the vicinity.  These persistent weak layers are now over a meter deep.  There haven't been any observations of collapsing or whumphing and we haven't seen any avalanches that we can definitely attribute to these layers in The Three Sisters mountains for almost a week.  Nonetheless, triggering an avalanche on these layers would be catastrophic.  I've been staying off of especially large slopes, and being careful to avoid trigger points and shallow unsupported slopes.

Avalanche Discussion

On Sunday I observed two large crowns on Middle Sister from very far away (road in to Tam Rim).  There was a large crown across the Diller glacier, and I believe I could also see a crown across the top of the east face.  Of course it is impossible to tell what type of avalanche they were, but the large propogation hints at a peristent slab.

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