Lawinenlagebericht

West Slopes South

Northwest Avalanche Center
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Lawinengefahr

Sat
Hochgebirge
2 · Mässig
Waldgrenze
2 · Mässig
Unterhalb
2 · Mässig
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Kernpunkte

The snowpack may begin a period of transition as warm and sunny weather impacts the zone on Friday. Steep sun-exposed slopes or high-elevation wind-loaded terrain will be the most likely locations for you to trigger an avalanche. Think about shaping your travel plans around the threat of larger and difficult-to-predict slides that often occur as we move from winter into spring.

Lawinenprobleme

  • Wind Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    1–1.5

    Cool easterly winds should continue through Thursday evening into Friday morning before tapering. On Friday it was reported that the wind was strong enough to move snow into fresh shallow slabs on lee features. Look for these unstable pockets near ridgelines, on convex slopes, or the sides of confined gullies. Due to the easterly wind direction, they may be on aspects where you’re not used to seeing them. Using small test slopes is a great way to test how they are reacting to your weight as a traveler. Visual clues such as textured surfaces, fresh drifts behind objects, or textured surfaces can help key you into the wind-loaded features you should avoid.

    (3/11/2023)

    Double cornice lines indicate that wind-loading could be present on both sides of the ridgeline.

    Photo: Robin Pendery

  • Loose Wet

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    1–1.5

    As winds die down and temperatures climb, expect Wet avalanche activity to increase on Friday. The first signs that the surface is destabilizing will be if it begins to get wet and sticky or if snow starts to shed from trees and rocks. Rollerballs and pinwheels on steep sun-exposed slopes are other indications that Wet Loose avalanches may soon follow. These slides will often start at a point and fan out as they descend, growing large and possibly even triggering slabs in the process. If this scenario starts to unfold, your best bet will be to head to shadier slopes, keeping aware of overhead hazards.

    The strong March sun could result in other avalanche problems, some of which are more difficult to manage. See the discussion for details.

    (3/14/2023)

    Natural loose wet avalanche near Crystal Mt on the first sunny day following a storm. 

    Photo: Andy Harrington

Avalanche Discussion

We are starting to transition from an unseasonably cold and snowy period that has spanned the last several weeks into a relatively warm and sunny spell over the next few days. The forecasted problem set listed above will likely cover the more in-your-face avalanche problems you’ll encounter on Friday. However, there is some growing concern for very large (D3) avalanches failing deeper in the snowpack. We have had a number of these lower likelihood, high consequence slides pop up in recent days throughout the Cascades, including multiple within the West South zone. The most common characteristics are that they appear to fail in high-elevation terrain that is likely wind-loaded. This includes multiple slides at Mount St. Helens and one in Mount Rainier National Park. 

With increased solar input this time of year, temperatures anticipated to slowly climb throughout the weekend, and a decrease in cool easterly winds, the concern becomes not just further destabilization of our wintertime snowpack. The threat of larger blocks of snow such as cornices or glides failing and triggering slides on the slopes below is in the back of our minds. Take these hard-to-predict scenarios into consideration when making your trip plans. Think about avoiding large alpine features as well as the terrain directly below, especially during periods of intense sunshine.

The upper snowpack around the West South zone is a bit aspect and elevation dependent.  Expect to encounter sun crusts and recently moistened snow on slopes that see direct sunshine. On the more shaded side of the dial, you're more likely to find layered cold dry snow. Signs of wind effect can be found on most aspects as you ascend in elevation. At the lowest elevations, a few inches of snow may sit atop a firmer crust formed due to rain earlier this week.

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