Avalanche forecast

West Slopes South

Northwest Avalanche Center
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Avalanche danger

Mon
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
3 · Considerable
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Highlights

Additional snowfall will maintain dangerous avalanche conditions within the West South zone on Sunday, particularly on the volcanoes. Regardless of your location, avalanches will trigger more easily on open slopes over 35 degrees, potentially running far and fast on a firm crust. Ease into terrain slowly and reevaluate the snowpack often. 

Avalanche problems

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–2

    You should continue to be leery of open slopes over 35 degrees on Sunday. Multiple rounds of precipitation during this stormy period have resulted in a layered upper snowpack sitting on a crust. Use test slopes or dig down to the crust with your hand or shovel to investigate these potential failure points before committing to terrain. You should also look for heavy snow over weaker snow (upside-down snowpack), cracking of the surface, or recent avalanches as indicators that the snowpack is unhappy. Slabs should be larger as you ascend in elevation or in wind-loaded terrain. Even if the storm snow is not showing much cohesion or failing in blocks during your tests, it could still run far and fast on the underlying crust on slopes over 35 degrees.

    (4/1/2023)

    A skier triggered Storm Slab on a convexity in the neighboring Snoqualmie Pass zone.

    Photo: Andy Harrington

Avalanche Discussion

The storm is not over for the West South zone, especially on the volcanoes. With roughly 20 inches already on the ground at Mount St. Helens and Paradise, forecasted precipitation may result in us approaching 3 feet of storm snow by Sunday evening. Closer to the crest, accumulations are closer to 8-12 inches with another 4-6 possible. Needless to say, you will find drastically different conditions depending on where you are out playing. You could find locally higher or lower hazard, so be prepared to make your own observations to determine avalanche potential and size.

A constant throughout the zone is that all of the recent storm snow should be overlaying a crust (3/31 interface). The bond and stoutness of this crust may vary by location, aspect, and elevation, but it should be a good snowpack marker when making your slope scale assessments. On Saturday, White Pass Pro Patrol reported shallow slabs triggered during their mitigation work, running on the 3/31. They also noted a few naturals occurred during the overnight hours during the height of the storm. Up at Crystal Mountain, the snow safety team relayed that they triggered both loose and slab avalanches during their morning efforts. Again, slides were running far distances on the underlying firm surface. No backcountry observations were received. 

Don’t expect the bond to become much more favorable by the time Sunday rolls around. The added precipitation just means that slabs will be thicker and with more layers for you to investigate. You could encounter periods of heavy convective showers interspersed with more sun breaks than we experienced on Saturday. Even in short spurts, this solar input could start to change the snow surface resulting in it gaining some cohesion and “slabbing up”. You might even see a few rollerballs and Wet Loose avalanches. It’s springtime, so conditions can change rapidly. Be sure to reassess the snowpack consistently throughout the day to see how the dynamic weather is affecting it.

Regions covered