Lawinenlagebericht

West Slopes South

Northwest Avalanche Center
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Lawinengefahr

Thu
Hochgebirge
3 · Erheblich
Waldgrenze
3 · Erheblich
Unterhalb
3 · Erheblich
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Kernpunkte

There is a lot of uncertainty around conditions, so keep your terrain selection mellow while we all gather information and let the snowpack heal. Slopes over 35 degrees, convexities, or wind-loaded terrain will continue to be the most likely locations for triggering avalanches on Wednesday. Be prepared for deeper snow and possibly larger avalanches on the volcanoes.

Lawinenprobleme

  • Storm Slabs

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

    As this storm cycle winds down, dangerous Storm Slabs will persist across the zone. The depth of these slabs will vary, with deeper slabs found on the volcanoes and in areas where the winds were able to transport snow onto leeward slopes near ridgelines. On Wednesday, you will be most likely to trigger avalanches on steep slopes, in wind-loaded terrain, on convex rollovers, or near rocky terrain such as cliffs and gullies. Using hand pits, test slopes, or looking for visual clues such as cracking will only key you into instabilities in the uppermost part of the recent storm snow. In order to get the full picture, you will need to dig down to the 2/11 interface to see how all of the recent snow has bonded. This interface was very reactive near the start of the storm cycle, resulting in some surprising avalanches on Saturday. If you find that the snow is unstable either near the surface or in deeper layers, dial back your terrain choices to avoid slopes over 35 degrees.

    (2/14/2021) This slab was triggered by skiers on Sunday (2/14) in the Crystal backcountry. The slab did not fail as the first skier descended, but a second skier and some additional sluffing snow were able to tip the scales. It is suspected to have failed on the 2/11 interface. [Photo: Andrew, Public Observation]

  • Deep Persistent Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    3

    The Mid-January crust/facet combo is over 7 feet deep at Paradise and closer to 5 feet near the crest. This may be too deep to be reactive to human triggers, but with a huge load recently added, we’re going to continue to be suspicious of these layers until we can gather more information. You should continue to stay away from big, steep, or open slopes, particularly at upper elevations. At all elevations, put a large buffer between you and large avalanche paths. This layer could possibly be activated if you trigger a large storm slab avalanche in the upper snowpack and may be more likely on slopes that get wind-loaded.

    (2/6/2021) This slab was intentionally triggered by a small cornice drop on Saturday (2/6) in the Crystal backcountry. It propagated widely and is believed to have run on the Mid-January crust/facet combo. [E aspect, 6300'. Photo: Jeremy Allyn]

Avalanche Discussion

Wednesday will bring a relative break to the active weather that has impacted our zone recently. Observations the past few days have been limited across the zone due to the hazards presented by the storm. However, NWAC forecasters and National Park Rangers were able to get a few observations from the Paradise area on Tuesday. The 16 inches of snow that had fallen overnight was reactive in stability tests and the 2/11 interface was found to be over 4 feet down (130cm), while the Mid-January crust/facet combo was found close to 8 feet down  (230-250cm)! They also found evidence of a widespread avalanche cycle from Monday, and that the wind was actively transporting snow onto leeward slopes. Lesser snow totals but similar reports came from Crystal Mountain on Tuesday. What this tells us is that natural avalanche activity is trending downward, but many slopes are now primed and ready for human triggers to come along. Keep your terrain selection conservative as we gather information on conditions and let the snowpack adjust to the recent load.

Additionally, slabs were failing on persistent grain types at the 2/11 interface on Saturday and surprising a lot of professionals and recreationalists. Now more deeply buried, we do not know if those grains have survived the cycle. If they have, avalanches could propagate widely, trigger remotely, or break in surprising ways. As we move into Wednesday, we may get some sun-breaks that could help to trigger some loose avalanches. Maybe at the lowest elevations these could be wet, but most of them should be dry. Look for these on steeper slopes starting at a point near trees and rocks before fanning out as they descend. These avalanches may also be triggered by humans on steep slopes where unconsolidated snow exists. With so much recent snow, any triggered avalanche, whether it’s loose or a slab, has the ability to gauge down and entrain snow, growing large. In fact, the recent snow is a real hazard all on its own due to its depth. You can learn more about snow immersion hazard here.

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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