Lawinenlagebericht

West Slopes South

Northwest Avalanche Center
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Lawinengefahr

Mon
Hochgebirge
2 · Mässig
Waldgrenze
2 · Mässig
Unterhalb
2 · Mässig
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Kernpunkte

Take note of how the snow surface is changing throughout the day due to the sun’s influence. When it starts to get sticky and wet or you notice snow shedding from trees and rocks, you should change your focus from dry avalanches toward wet avalanches and head toward shaded slopes.

Lawinenprobleme

  • Loose Wet

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

    As temperatures creep up and the sun grows stronger throughout the day, expect wet avalanches to become more prominent on steep sunny slopes. Your first indicators that the upper snowpack is destabilizing will be rollerballs and pinwheels, snow shedding from trees and rocks, and the surface becoming wet and sticky. If you notice these signs, expect Wet Loose avalanches to follow and head toward shadier slopes. These slides often start at a point such as near trees or rocks, can entrain significant snow, and will fan out as they descend, possibly growing large and traveling long distances toward lower elevations. 

    (3/25/2021) Wet Loose activity, such as rollerballs and small avalanches will become more prevalent as the April sun destabilizes the recent storm snow. [Photo: John Darmody]

  • Wind Slabs

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

    Plenty of wind-affected snow still exists as you ascend in elevation, and cold dry snow will be more likely to escape the sun’s influence on northerly slopes later in the day. Take a look for freshly built cornices, textured snow surfaces, or new drifts behind trees or other objects to help you identify wind-loaded slopes to avoid. Wind Slabs could be hidden under a couple of inches of fresh snow, so feel for subtle changes as you travel to help you determine if you stumbled upon one without knowing. Wind Slabs will be more likely near rocky features such as the confined gullies or at the base of cliffs, on leeward slopes near ridgelines, or on convex rollovers. You can use uptrack tests or test slopes to determine how the recent storm snow is reacting to your weight and if slab potential exists. If you find poorly bonded snow or suspect terrain to be wind-loaded, you should seek out lower-angled slopes. 

    (1/23/2021) Cracking in the snow surface as you travel can help clue you in that the upper snowpack is unstable and may produce slab avalanches.

Avalanche Discussion

The West South received another 4-6” in Friday night’s storm, but the wind was the real story. Winds topped 100mph at multiple NWAC weather stations around the zone and we received reports of wind-affected snow and Wind Slabs. This comes on the heals of receiving up to 8” of snow in Wednesday night’s storm, making it a snowy and breezy week throughout the zone. All of the recent storm snow sits atop of a stout crust (4/7 interface) in most locations and we expect all avalanche activity on Sunday to occur above this interface. Avalanches have the ability to run far and fast on this crust and could fail at multiple points in the recent storm snow.

Things should start to change on Sunday, which should be day 1 of what projects to be a multi-day shedding event/wet avalanche cycle. Transition days can be difficult, and your morning concerns could be more focused on dry avalanche problems such as Wind Slabs or Dry Loose. As the sun gains influence and warms surfaces, the transition to wet avalanche problems may happen quickly, manifesting in different types of avalanches. Snow will start to shed from trees and rocks, falling onto the slopes below and possibly triggering Wind Slabs or starting loose avalanches - either wet or dry. Both fresh and mature cornices exist throughout the zone, and more could fall under the sun’s influence, triggering slabs or starting loose slides. The sun's influence could even cause the recent snow to "slab up" and become more reactive on steep slopes.

Wet avalanches are generally not well understood and difficult to predict, so it could take a few days for all of these scenarios to play out. But Sunday should be the start of this transition and you should keep in mind that multiple near-misses and avalanche involvements have occurred around the Cascades over the past week as we have navigated flip-flopping springtime weather. This recent history combined with the uncertainty around these shedding events should lead you toward a more conservative mindset and terrain selection.

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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