Lawinenlagebericht

East Slopes North

Northwest Avalanche Center
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Lawinengefahr

Sat
Hochgebirge
4 · Gross
Waldgrenze
4 · Gross
Unterhalb
3 · Erheblich
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Veraltet — dieser Lagebericht ist 5 years ago abgelaufen. Du siehst vergangene Verhältnisse, nicht den aktuellen Bericht.

Kernpunkte

Expect dangerous conditions near and above treeline where west wind will build fresh slabs through the day. Avoid wind-loaded slopes steeper than 35 degrees at upper elevations. You may be able to trigger small loose avalanches on steep shaded slopes below treeline. 

Lawinenprobleme

  • Wind Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Very Likely
    Größe
    2

    Strong westerly winds will continue to transport snow onto lee slopes on Friday. The most dangerous slopes will be near and above treeline. You may even find slabs in open areas below treeline. Avoid wind-loaded, leeward slopes 35 degrees and steeper. Steer around thickly loaded, pillowed features and convex rollovers. Fresh wind slabs will grow bigger and become easy to trigger as the day goes on. Shooting cracks or hollow-sounding snow are signs you could trigger an avalanche on similar nearby slopes.  Steer around obvious wind features,  thickly loaded leeward slopes, and unsupported features. 

  • Loose Dry

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Likely
    Größe
    1

    You could trigger loose avalanches on steep, wind-sheltered slopes in the storm snow.  Use caution on convex and unsupported terrain features and around terrain traps like gulleys and cliffs. Use test slopes and quick snowpack tests to assess how this new snow is bonding. If in doubt, stick to slopes less than 35 degrees.

    (1/31/2021) An example of storm snow that slides easily and could result in an avalanche on slopes steeper than 35 degrees. Photo: Josh Hirshberg

Avalanche Discussion

On Thursday, avalanches were easy to trigger and even ran naturally to size D2. Observers had a close call when a natural avalanche dusted them with a powder cloud from the Cutthroat slide paths on Highway 20. Southwesterly winds formed reactive slabs on leeward slopes near and above treeline. Observers reported a widespread cycle of avalanches up to size D3 that ran during the day and into the night of the 22nd. Most were due to wind loading near and above treeline at the base of cliffs, though some may have been in wind-sheltered terrain. One notable slide was 1-2ft deep and propagated 300ft across. It appears that all avalanches ran within the recent snow or at the interface of new and old snow. 

Persistent slab avalanches are unlikely but could still exist in the eastern mountains. On Wednesday 2/17, an observation from the Twisp River drainage in the near treeline band found the mid-January facet/crust combo unreactive in snowpack tests and over 3 ft down.  Buried surface hoar slightly closer to the surface,  less than 3' or 80 cm down, showed sudden results in snowpack tests. This layer may again be a problem in the outlying eastern parts of the zone. Further west, the last persistent slab avalanche occurred near Rainy Pass on Feb 8th (see photo below). It is suspected to have run on the mid-January crust-facet layer about 2-3ft below the snow surface. 

During the ongoing Covid-19 pandemic, continue to follow the latest guidance from local, state, and federal health officials. Avoid unnecessary risks that could impact first responders and stress medical resources. Wear a mask when appropriate, practice social distancing, and consider recreating closer to home.

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