Bollettino valanghe

West Slopes South

Northwest Avalanche Center
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Pericolo valanghe

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

The potential size and reactivity of avalanches involving the recent storm snow will vary greatly throughout the West South zone on Monday. The threat of larger avalanches increases the further south you travel, specifically on Mount St. Helens. Look for red flag signs of instability such as recent avalanches, cracking of the surface, or changes to the snowpack due to springtime weather as indications to dial back your terrain selection.

Problemi valanghivi

  • Storm Slabs

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

    Take the time to investigate all of the snow over the 3/31 crust for potential points of failure before committing to terrain on Monday. Depending on your location, you may have to dig down a few feet with your shovel or could reach this interface by quickly digging with your hand. Apart from the mid-storm layers that could fail, you’re looking for heavy snow over weaker snow (“upside-down" snowpack), or areas where the snow is failing in cohesive blocks. Throughout much of the zone, you’ll want to focus your attention on steep unsupported slopes, confined chutes/gullies, convexities, or wind-loaded terrain where triggering an avalanche is more likely. On the volcanoes, however, you should consider avoiding all open slopes over 35 degrees.

    Loose avalanches will also be a concern on slopes over 35 degrees throughout the forecast area. While often thought of as a manageable problem by some backcountry travelers, don’t get surprised or tripped up by one in consequential terrain. They could run far distances on the underlying crust.

    (4/2/2023)

    A mid-storm layer failing during a shovel tilt test ~28cm deep and 7cm above the 3/31 layer.

    Photo:

Avalanche Discussion

This forecast is not without a high degree of uncertainty. You will likely find locally higher hazard on the volcanoes, specifically Mount St. Helens where close to 3 feet of snow has fallen since Friday. Storm accumulations lessen the further north you travel in the zone with White Pass and Paradise coming in close to 2 feet and Crystal around 1 foot. The snow showers aren’t ready to stop, either. We should squeeze out another few inches by the time Monday wraps up. 

All of this snow is sitting above a crust (3/31 interface) that should be an easily identifiable snowpack marker for your assessments. We do not expect any avalanche activity below this interface at this time. On Sunday, NWAC forecasters in the Crystal Mountain area found that storm snow was generally light but consistently failed on a subtle layer a few inches above the 3/31 interface. On slopes that see direct sunshine, the cold and dry surface quickly gained some cohesion and became a bit upside-down during a short sun break. As clouds moved back into the area, the surface again stiffened up, creating a subtle sun crust. 

The behavior on display at Crystal is the game we play in the springtime. On Monday, we’re anticipating interspersed periods of sunshine and convective snow showers. Generally speaking, less snow and more sun breaks are expected than what we experienced on Sunday. We may also see an uptick in winds. Expect similar results as to what was experienced during Sunday’s sunny weather at Crystal. If there is prolonged sunshine or more frequent breaks, you could see Wet Loose avalanche activity start to develop or some touchy slabs. With cold dry snow already in place, you may even see some shallow Wind Slabs forming on leeward features if those winds play out.

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