Bollettino valanghe

East Slopes North

Northwest Avalanche Center
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Pericolo valanghe

Sun
Alta quota
3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
3 · Marcato
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In sintesi

Expect dangerous avalanche conditions to develop on Saturday. Avalanches may run naturally with the storm snow, and in some areas you could trigger an avalanche that becomes large and runs on weak snow near the ground. Saturday will be a good day to step it way back, use non-avalanche terrain, and carefully observe how the storm shakes out.

Problemi valanghivi

  • Storm Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    1.5–2.5

    We could see a round of natural avalanches on Saturday morning as storm snow piles up fast. Slabs could fail on lower density layers beneath, on recently buried layers of surface hoar, or in some areas even on old weak snow near the ground. Slides may be soft and small in nature, or they could be large and dangerous if they pull out old snow. Conditions may remain touchy during the day, and it may take some time for the snowpack to adjust to this load. The upslope nature of this storm may put down a significant blanket of new snow in the eastern part of the zone. These areas where the snowpack is shallow are some of the more likely places we could see avalanches near the ground. 

    If you go out, make sure you are confident in observing red flag signs of instability like whumphing collapses, shooting cracks and fresh slides. Work with your partners and discuss how to stay safe while traveling in the mountains given the conditions you experience. 

    Example storm slab avalanche near Highway 20 from a previous season.

    Photo: Adam Butterfield

Avalanche Discussion

This is shaping up to be a significant storm for the zone. The upslope nature of the storm means that contrary to the usual where more snow falls at Washington Pass than further east, we're looking at an even blanket of a foot or so throughout the eastern foothills. On Thursday, about 3" of snow fell at Washington Pass and covered up a mixed bag of surfaces. At this interface, you'll find sun crusts on steep south slopes, firm wind board, soft, weaker snow, and potentialy large surface hoar. While surface hoar may have been blown over by wind in some areas, its likely preserved under the surface of wind-sheltered slopes.

Check out Josh's obs of Goat Peak just north of Mazama from Monday. Snowpack tests were easy and impressively reactive with propagation where he found older drifted slabs. He, and a separete party in the area reported collapses in open terrain below treeline and one at as high as 6750ft. Cold temperatures and shallow snow have kept the snowpack weak in these eastern mountains.

You can find facets from mid-November (buried 11/22) just below the middle of the snowpack on most slopes from Washington Pass into the eastern mountains. It's uncertain if they remain intact as far west as Rainy Pass. We haven't received reports of avalanches on this layer, but it's been the source of numerous reports of collapsing, mostly at lower elevations. The grains appear to be bigger and "sharper" further east. Near and west of Washington Pass and below about 7,000ft the facets received rain and you'll find them just beneath a crumbly crust. The overlying snowpack also varies from west to east with elevation. It's generally deeper as you move west and higher in elevation. Overall, the weak layer seems most problematic where the grains are the biggest, closer to the surface, and have a stiffer slab immediately on top. Big storms could create avalanches on this layer.

The weather forecast carries a fair amount of uncertainty, so be ready to make your own assessments of the snow and avalanche conditions as it plays out. Let us know what you see by submitting observations.

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