Bollettino valanghe

West Slopes South

Northwest Avalanche Center
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Pericolo valanghe

Wed
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
2 · Moderato
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In sintesi

Focus your attention on steep unsupported slopes, convexities, or chutes where you’re more likely to encounter wind-loading and trigger an avalanche on Tuesday. Expect to find higher hazard and larger slabs the further south in the zone you travel. Make travel plans with plenty of options to adapt to changing snowpack conditions as a result of springtime weather.

Problemi valanghivi

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–2

    Wind affected terrain features may be the most likely location for you to trigger an avalanche on Tuesday. Depending on your location, identifying wind-loaded slopes could prove to be a challenge. The signs may be subtle such as noticing a lightly textured surface or feeling the density of the snow change as you travel. In some cases, slabs could be buried beneath a few inches of low-density snow. On the flip side, more in-your-face observations such as actively blowing snow forming new slabs should be easy to spot. Regardless of how easy they are to identify, you should be leery of steep unsupported slopes, convexities, confined chutes/gullies, or the lee side of ridgelines. These are the most likely locations to trigger one of these avalanches. 

    On Mount St. Helens, you could encounter larger and potentially more widespread avalanche potential. Be sure to question any open slope over 35 degrees whether you suspect that it is wind-loaded or not.

    (4/3/2023)

    A group intentionally triggered this Wind Slab by dropping a small cornice on the slope. It failed 6-10" deep. [White Pass E/SE 6500']

    Photo: Susie Glass

Avalanche Discussion

If you’re traveling to Mount St. Helens, you should consider taking a look at the Hood forecast first. It may be more applicable. 

The weather pattern makes it feel a bit like Groundhog Day out there. Periods of sunshine and convective snow showers should again impact the West South zone on Tuesday. As has been the case throughout this stormy period, areas further south should see more snow and wind, while areas further north or closer to the crest could see more sun breaks. This dynamic and somewhat unpredictable springtime weather playing out over a large zone results in plenty of if/then statements in the avalanche forecast. 

You might encounter Dry Loose slides (sluffs) that could grow large or run far distances. Of course, if the sun is able to break through and affect the surface, you may see the moisture content start to transition toward Wet Loose avalanches. In some locations, solar input could also help the upper snowpack gain cohesion as was noted on Sunday near Crystal Mountain. This could increase the potential for slab avalanches. To simplify things, the steeper the slope, the more likely you are to trigger an avalanche in the recent storm snow. The further south you are in the zone, the larger that avalanche could be. 

On Monday, avalanche professionals in the White Pass backcountry reported close to 2 feet of snow sitting atop the 3/31 interface. The snow was generally right-side-up but did contain midstorm layers that were highlighted with shovel tilt tests. They did not find the layer a few inches above the 3/31 crust that was reported by NWAC forecasters near Crystal Mountain on Sunday. They also found wind-drifted snow that was easy to trigger with ski cuts and cornice drops, producing avalanches with 6-10 inch crowns. 

We received reports of a handful of human-triggered avalanches near Crystal Mountain this past weekend. Most were on steep slopes, some of which may have been sun-effected. We have not received any information from the volcanoes where the bulk of the storm hit. But with a few inches of snow falling each day, you’ll want to check everything above the 3/31 interface for potential issues. Its depth increases from roughly 1 foot below the surface at Crystal Mountain to approximately 2.5-3 feet below the surface at Mount St. Helens.

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