Bollettino valanghe

East Slopes South

Northwest Avalanche Center
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Pericolo valanghe

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2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
1 · Debole
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In sintesi

Friday will be a messy day, and the type of avalanche you encounter will depend on what's falling out of the sky: rain, snow, or freezing rain. At upper elevations, you could trigger a small avalanche in wind-drifted snow or wet avalanches with rain on dry snow.  Cracking in fresh snow or rollerballs are signs to steer around steep slopes.

Problemi valanghivi

  • Loose Wet

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–1.5

    Rain on dry snow, rollerballs, and sticky snow surfaces are the first signs of increasing potential for wet loose avalanches. These slides can start naturally from cliffs, trees, or rocks shedding snow, or you could trigger one on a steep slope. If you start to see signs of wet snow, choose smaller or low angle slopes to reduce your risk. Remember to look at what terrain is above you as well, as a chunk of wet snow hitting you from above can easily ruin your day. Factors limiting the potential for large wet avalanches include surface crusts on southern slopes, freezing rain crusts at lower elevations, and minimal precipitation in the forecast. With these in mind, we expect these to be small and relatively difficult to trigger. Areas of greater concern are those without prior surface crusts from freezing rain or sunny days. 

    (2/4/2023) 

    Rollerballs like these are one of the first signs of wet avalanches. 

  • Wind Slabs

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

    If you brave the weather to climb into upper elevations, you may encounter small wind slabs near ridgelines. Look for textured surfaces, actively blowing snow, or cornice formations to identify wind loaded slopes. With minimal precipitation, we expect these to be isolated to small pockets. That said, weak snow surfaces are lingering around, and these avalanches could be quite easy to trigger. Consider the consequences of a small avalanche if you are on a slope that can push you into gullies, trees, or over cliffs. Cracks that shoot away from you are a sign to steer around deep drifts on steep slopes. 

    (2/28/2023)

    Look for these pillow-like drifts to help you identify slopes of concern. 

    Photo: Katie Warren

Avalanche Discussion

The East South Zone is likely to receive significant freezing rain overnight on Thursday. This could create a thick ice crust on the snow surface at most lower elevations and potentially extend into the mid-elevations. While this will make travel conditions unpleasant, it will help limit widespread wet avalanche activity. The mixed precipitation makes for a tricky forecast, and valley-to-valley conditions might differ significantly on the east slopes of the Cascades. Rely on precipitation type and surface conditions to understand the most probable avalanche problem for where you are traveling. Freezing rain or other surface crusts will limit wet, loose avalanches, whereas rain on dry snow is likely to increase the hazard. With snow and wind, focus on dry snow problems such as storm and wind slabs. 

There is shallow coverage at lower elevations, but a more substantial snowpack at mid-elevations, particularly in more open terrain. Snow surfaces on steep southern slopes have thin surface crusts, while other aspects have preserved dry snow with potentially weak surfaces. Overall, the snowpack structure is favorable, with two prominent crusts. The upper crust, buried ~9", is thin and was buried on 12/24. The lower crust is thicker, was buried on 12/18, and likely extends into upper-elevation terrain. The base of the snowpack is a thick layer of melt forms from the major December atmospheric-river event. 

Other than this one aging data point and telemetry data, we have no other snowpack information for the zone. Subtle changes in aspect, elevation, or canopy cover can significantly affect overall depth and riding conditions. Snowpack depths likely range widely across the East South. Expect a lean snowpack of roughly 20-30 inches in the eastern mountains and more robust 50-60 inches closer to the Cascade Crest. Where the snowpack is thin, downed trees, open creeks, and grabby bushes make getting to deeper snowpacks a challenge. Plan extra time into your day to navigate these obstacles.

You can help us out! Submit an observation on the avyapp or here.

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