Lawinenlagebericht

West Slopes Central

Northwest Avalanche Center
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Lawinengefahr

Thu
Hochgebirge
2 · Mässig
Waldgrenze
2 · Mässig
Unterhalb
2 · Mässig
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Kernpunkte

Storm totals vary across the West Central zone meaning you'll need to do some homework on conditions before committing to a slope. You’re most likely to trigger an avalanche on wind-loaded features such as convexities or confined gullies, regardless of your location. On open steep slopes, you may encounter loose avalanches that could grow large given the right circumstances.

Lawinenprobleme

  • Wind Slabs

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

    We’re anticipating the most likely location for you to trigger an avalanche on Wednesday will be on slopes where the wind has drifted snow into stiffer slabs. Look for Wind Slabs near ridgelines, on convex features, or near rocky terrain such as the base of cliffs or confined gullies. These slabs should be slightly stiffer than the surrounding low-density snow but likely won’t be Hard Slabs. Feel for changes in the consistency of the snow as you travel to help you identify the areas we’re concerned about. Wind-loaded features may look “pillow-like” or “fat” compared to the surrounding terrain and you might notice some textured surfaces nearby. If you suspect a slope to be wind-loaded, simply choose a simpler route to avoid it.

    (1/9/2023)

    Example: Shallow, reactive wind slabs in sheltered terrain in the Mountain Loop earlier this season. Note the convex nature of the slope.

    Photo: Irene Henninger

  • Loose Wet

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

    A mostly sunny day on Wednesday means solar-induced loose avalanches could again present a problem. Observations from Tuesday indicate that some slopes started to tip the scales in neighboring zones but did not produce a widespread loose cycle. 

    These avalanches start at a point and fan out as they move downhill. They’ll be most likely on steep slopes over 35 degrees that see direct sunshine and could be preceded by rollerballs or pinwheels. You may see them initiated by snow shedding from trees or rocks even if the snow surface isn’t wet and sticky - manifesting more like a Dry Loose. Regardless of the moisture content, their behavior and management remain the same. If you notice the signs, don’t get tripped up by one in consequential terrain and you can always head for shadier slopes to avoid them altogether.

    (2/14/2023)

    Loose avalanches triggered by snow shedding from trees and rocks were observed on 2/14 in the neighboring Snoqualmie Pass zone. Although triggered by sunshine, most of these involved dry snow.

    Photo: Andy Harrington

Avalanche Discussion

A convergence zone took aim at the West Central on Monday night and likely delivered significant snowfall accumulations to the southern half of the zone. We often talk about how the northern half is snowier and potentially more dangerous, but on Wednesday it could be the opposite. 

Observations from the zone are basically non-existant, which comes as no surprise. But reports from the neighboring West North zone indicate that small avalanches were triggered near ridgelines in wind-loaded terrain by skiers and that small loose avalanches occurred in the sunshine. From further south, the neighboring Snoqualmie Pass zone also received the brunt of the convergence and picked up around 2 feet of new snow at upper elevations. At least 1 large avalanche was observed by NWAC forecasters along with multiple small loose avalanches.

This information all lines up well with what our expectations for Wednesday are in the West Central zone. While the depth may vary from north to south, expect to find the 2/13 interface anywhere from 1 to 2 feet below the surface. This is the snow where you should focus your attention and where we anticipate the majority of avalanches will occur. On slopes that see direct sunshine, a slight crust may have formed on the surface. Shadier slopes will likely continue to harbor cold dry snow. 

That said, in both the neighboring West North and Steven’s Pass zones, there have been recent avalanches triggered on deeper layers in the snowpack when we were not expecting them. Take this information with you as part of your trip planning and consider taking a look for deeper instabilities in the snowpack before stepping into consequential terrain at upper elevations.

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