Lawinenlagebericht

West Slopes South

Northwest Avalanche Center
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Lawinengefahr

Wed
Hochgebirge
3 · Erheblich
Waldgrenze
3 · Erheblich
Unterhalb
2 · Mässig
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Veraltet — dieser Lagebericht ist 6 years ago abgelaufen. Du siehst vergangene Verhältnisse, nicht den aktuellen Bericht.

Kernpunkte

New snow, wind, and rising temps will meet weak snow surfaces creating dangerous avalanche conditions. You will be able to trigger an avalanche large enough to bury you in steep terrain where winds have drifted the snow or in the afternoon when the temperatures rise and more snow has accumulated. The volcanoes will have the highest hazard with this weather pattern, but no matter where you are, new snow will fall on weak surfaces. Travel cautiously and when in doubt choose lower-angle terrain.

Lawinenprobleme

  • Storm Slabs

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

    Strong SW winds will accompany fresh snow and rising temperatures Tuesday. New snow will fall on soft and weak snow surfaces that rest above a firm melt-freeze crust. Expect the avalanche danger to be highest on the volcanoes, but all parts of the West South zone have weak snow above a strong crust and the snowpack will struggle to accept heavy fresh snow.

    Expect shallower storm slabs at lower elevations and wind-sheltered areas. At middle and upper elevations, expect larger slabs and do not rule out the effect of moderate to strong winds. New snow will be wind transported to lee slopes. You will likely be able to trigger a wind slab on lee slopes steeper than 35 degrees. Avalanche hazard will be highest later in the day as more snow accumulates and temperatures warm slightly.

    Shooting cracks, heavy snow over light snow, collapsing, and whumping sounds are signs that you could trigger an avalanche. At higher elevations and near ridgelines where wind deposited snow is accumulating, use cornices, pillow-like drifts, and cracking in the snow as visual clues of wind slab formation and avoid steep slopes, convex rolls, and cornices where you see these signs. 

    If you see evidence of slab formation, choose slopes below 35 degrees and steer around cornices, convex rolls, and unsupported slopes.

    (11/25/2020) Test slopes can give you a lot of good information about how new snow has set-up after or during a storm. This test slope shows that wind slabs are sensitive and propagating easily.

Avalanche Discussion

Last week, warm temperatures followed by a rain event helped to create a stout crust (12/9) throughout the West South. This thick crust is being considered our new ground for the time being and close to a foot of snow can be found sitting on it on the volcanoes. Other areas of the zone contain far less snow on the crust, resulting in locally lower avalanche hazard. Regardless of depth,  the snow on top of the crust has remained mostly light and fluffy without much cohesion, except for in specific areas where the wind was able to drift the snow into stiffer slabs. This light and fluffy snow contains some weak snow crystals that we are watching as we continue to increase the load over the next few days. If you find that the snow is no longer powdery but is more cohesive, the possibility of avalanches is increasing and you may be dealing with a Storm Slab problem and you should default to slopes lower than 35 degrees. Don’t get caught off guard as we move through the different waves of storms this week, the hazard will be increasing at some point.

Recent weather wreaked havoc on the snow in the West South. Firm surfaces abound under the recent fresh snow and many previously buried obstacles have recently reemerged. You’ll need to navigate around numerous open creeks, downed logs, and areas of thin coverage. New snow will help, but realize that these obstacles now may be shallowly buried until we have a few more storms come through. Be cautious and give yourself extra time to manage these variable travel conditions.

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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