Boletín de aludes

East Slopes Central

Northwest Avalanche Center
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Peligro de aludes

Sat
Alta montaña
3 · Notable
Límite del bosque
3 · Notable
Bajo el límite
2 · Moderado
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Desactualizado: este boletín caducó 3 years ago. Estás viendo condiciones pasadas, no el boletín vigente.

Lo esencial

A storm favoring the east slopes of the Cascades will impact the area overnight on Thursday. Expect new snow, wind, and dangerous avalanche conditions on Friday. Watch for signs of instability, such as shooting cracks or recent avalanches. Travel on low-angle slopes and avoid areas where the wind has drifted snow into deep slabs on lee aspects.

Problemas de aludes

  • Storm Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Likely
    Tamaño
    1–2

    This storm isn't typical for the Pacific Northwest, and you can anticipate more snow in areas east of the Cascade Crest. You could trigger storm slab avalanches on steep slopes and convex rolls in the new snow. It will be best to let the storm run its course and stick to low-angle terrain on Friday. Watch for signs of instability, such as shooting cracks, collapsing, or recent avalanches. You can also make observations as you travel using small test slopes and quick hand pits to assess how the new snow reacts. Snow that slides easily in a cohesive block indicates that triggering an avalanche is possible. The recent snow is incrementally burying various old crust layers. While we haven't seen any avalanches on these layers in East Central, the potential exists for avalanches on deeper layers. Account for this uncertainty by dialing back slope angles down on Friday.Moderate to occasionally strong winds are also in the forecast, so anticipate sensitive wind slabs developing at upper elevations below ridges and in wind-exposed areas. Use visual clues such as textured surfaces, deep pillowlike drifts, or feel for stiff over soft snow layering to identify likely wind slab locations. Wind slabs may be larger and easier to trigger than storm slabs, so avoid steep slopes and potential trigger spots such as the base of cliffs and slopes below corniced ridges. 

    (12/20/2022)

    Small test slopes like this are a great way to observe how the new snow reacts. 

    Photo:

Avalanche Discussion

There is quite a bit of uncertainty with the incoming storm, but anticipate 6-10 inches of new snow with moderate to occasionally strong winds in the East Central. Snowfall amounts are likely to vary throughout the zone, with greater amounts near Mission Ridge and Leavenworth and lower storm totals in areas further west. If you find deep new snow, then you'll likely be able to initiate small sluffs that run on steep slopes. You'll want to exercise caution near terrain traps like above cliff bands or tight gullies where a fast-running sluff could knock you off your feet in the wrong place. 

Recent observations indicated the recent snow is low-density snow that lacks slab structure. Joe Dellaporta observed nice riding conditions, soft snow surfaces, and little wind effect on Thursday at Blewett Pass. On Wednesday, I was out in the northern Chiwaukum Range and found about a foot of recent snow with little signs of instability below 5000ft. Another observer on Wednesday, in the Mission Ridge backcountry, found new snow was sluffing on steep slopes. Last week there were isolated small storm slabs on various crust layers on southern aspects.

The recent soft snow rests over a couple of intermittent sun crusts and a pair of rain crusts from Valentine's Day, which can be found 1-3ft deep. These often present as a crust/facet/crust sandwich, with weaker snow beneath the upper crust. Observations indicate wide variability in the structure and depth of this layer throughout the zone. There are isolated observations with signs of instabilities on this layer in the Icicle drainage and the eastern Highway 2 Corridor. On Monday, observers near the Swath on the western edge of the zone reported small collapses on this layer on a north aspect between 5,600ft and 5,800ft. Snowpack tests on the adjacent slope produced propagating test results but not on a similar slope nearby. Considering the uncertainty with the potential for avalanches on this layer, it is worth sticking to low-angle slopes during this larger storm on Thursday and Friday.

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