Avalanche forecast

East Slopes North

Northwest Avalanche Center
View on map

Avalanche danger

Mon
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
2 · Moderate
Open full map
Out of date — this forecast expired 4 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

Sun and warming temperatures may help settle the new snow, but it may also create more of a cohesive slab. Heed signs of instability like whumphing collapses, cracking, and steer clear of steep slopes if you find them. In areas that previously held a shallow snowpack, you could trigger large avalanches that run on weak snow near the ground.  

Avalanche problems

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1.5–2.5

    Anywhere from 8-12" of storm snow will take some time to settle out. Conditions may remain reactive during the day on Sunday, or even increase in sensitivity as warm temperatures and some sun may cause the upper layers to become heavier and more cohesive. Winds also may have created thicker, deeper pockets that are now hidden under soft snow. Avalanches could run on lower-density layers at the old/new interface, on recently buried layers of surface hoar, or in some areas even on 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.

    The upslope nature of Saturday's storm put down a significant blanket of new snow in the eastern part of the zone. These areas where the snowpack is shallow, and are some of the more likely places we could see avalanches near the ground. 

    Be dilligent and look for 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

Storm totals ranged from 0.5" (Wa Pass) to 1.2" (Harts Pass) of SWE in the zone on Saturday with 8-12" of new snow. An observer reported widespread whumphing collapses between 2,600 and 3,600ft on east aspects near Sun Mountain. Near Kangaroo on Thursday, Willie spotted an older slide that appeared to have run on a deeper layer (see photo below). 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.

Be ready to make your own assessments of the snow and avalanche conditions. Let us know what you see by submitting observations.

Regions covered