Avalanche forecast

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Northwest Avalanche Center
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Avalanche danger

Fri
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
3 · Considerable
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Highlights

Expect increasingly dangerous avalanche conditions on Thursday, with storm slabs easy to trigger and potential for buried weak layers to become active. Avalanche danger may become High by the end of the day with heavy snowfall and gradually warming temperatures. Step it way back, and take into account your exit plan. 

Avalanche problems

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1.5–2

    Around 6-10" of heavy snow may fall by the end of Thursday. This, accompanied by a gradual warming trend is likely to create 'upside down' storm snow. Storm slabs could be easy to trigger, and begin to fail naturally by late afternoon. To complicate matters, slabs may just be the depth of the new snow, but there are a few deeper, weak layers that could make for surprising and larger avalanches if they step down. Slides could run down from upper elevations and cover access roads.

    If you head out, make sure you can clearly identify what is and is not avalanche terrain. Heed signs of danger like shooting cracks and fresh, shallow avalanches on small steep slopes. 

    (1/8/2023)

    Example storm slab in terrain below treeline.

    Photo:

  • Persistent Slabs

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

    The weight of the new snow will begin to stress buried persistent weak layers. The distribution of these layers seems patchy, but two recent ski triggered avalanches point to the presence of them. You're most likely to find these outside of wind affected areas, in sparse trees and on north to east aspects. This is where you could find buried surface hoar from around January 4th, or weak faceted snow on or beneath a slick crust from Christmas. On Tuesday, a skier triggered a large slab on a north aspect at 4,800ft near Silverstar, so we should take this as bullseye evidence. You can look for long shooting cracks as you travel, and check for planar failures with a variety of tests. Both parties that have triggered slides in wind sheltered terrain reported no signs of instability beforehand, so the absence of information doesn't necessarily mean stability.

    Hedge your bets by staying away from steep slopes in terrain described above, especially as snow begins to pile up. 

Avalanche Discussion

Expect the snow to accumulate steadily throughout the day on Thursday, gradually warming temperatures, and dangerous avalanche conditions. Plan for increasing danger with your exit in mind, as avalanches could run naturally by the end of the day. A report of a large ski triggered slab on a north aspect at 4,800ft came in from the Silverstar Creek area on Tuesday. The slide did not occur in wind affected terrain, but in sparse trees. This is information to take into account as the next storm gets going and folks hunt out better visibility and areas that are typically considered safer. Theres a great deal of uncertainty about the distribution and reactivity of the weak layer that caused this avalanche. Other avalanches of note:On Sunday, a party reported triggering a small slab near Varden Creek on a north aspect at 6,000ft. The skier that triggered the slide was the fourth on the slope, and got carried a little ways but was luckily ok.  WSDOT forecasters reported a wet avalanche that gouged to the ground near the town of Methow. On Saturday, an observer near Twisp reported a mix of snow and rain with a similar avalanche gouging to the ground.

On Monday, Willie reported two small soft slab avalanches hit the closed Hwy 20 in the Liberty Bell group on Monday morning. Winds were strong with intense blowing snow in the morning, then skies broke and the wind calmed down. Shallow storm slabs were easily triggered about 8" down. Tests showed potential for failure down about 1ft and 1.5ft on large, preserved stellars.

The last cycle of very large avalanches occurred December 24-27th near Washingotn Pass involving older weak layers that were buried in late November and early December. In the majority of the zone, the crust from Christmas is stout and avalanches are unlikely to fail beneath it.

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