Boletín de aludes

East Slopes Central

Northwest Avalanche Center
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Alta montaña
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Límite del bosque
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Bajo el límite
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Desactualizado: este boletín caducó 5 years ago. Estás viendo condiciones pasadas, no el boletín vigente.

Lo esencial

You may be able to trigger wet avalanches in steep terrain, especially on sun-exposed slopes. Use caution if traveling in high consequence terrain. Very large avalanches that run into seemly safe terrain below are also possible in specific areas. Choose routes that limit your exposure from large alpine terrain above.

Problemas de aludes

  • Loose Wet

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

    Overnight temperatures above freezing and warmer temperatures in the forecast on Friday will sustain the possibility of triggering wet loose avalanches in steep terrain. We have little to no information on the upper elevations to confirm if overnight cooling has allowed a crust to form on the surface. But with daytime warming, even any crusts formed overnight may break down during the day. With a sunny day forecasted tomorrow, southern aspects are more likely to have unstable wet snow. It may be best to travel on sun-exposed slopes in the morning hours before the sun, and warm temps melt the snow surface. Inversion conditions may keep the valleys cooler and cause a slightly elevated hazard for wet loose avalanches at upper elevations. 

    Rollerballs or small test slopes where wet snow gains momentum and additional snow as it flows downhill are good indications that wet loose avalanches are possible. Also, be cautious of traveling above rocks, cliffs, creeks, or other obstacles that can increase the consequences of getting caught.

    (1/13/2022) Large wet avalanche off of Icicle Ridge. Likely occurred on 1/12/2022 or 1/13/2022

    Photo: Katie Warren

  • Wet Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Possible
    Tamaño
    2–3

    Wet slab avalanches are notoriously hard to predict.  But multiple nights of above freezing temperatures, higher temperatures in the forecast, and solar radiation might be the tipping point to these very large avalanches running on deeply buried weak layers. The slab overlying these layers may now consist of moist snow, and water pooling on crusts or weak layers within the snowpack can initiate these very large avalanches. This problem is likely in the Wenatchee Mountains and areas further East of the crest. While many of these large avalanche paths have previously slid during the Jan 5-8th storm, there may be slopes with lingering deep instabilities. While this is a low likelihood, high consequence situation, being caught in or underneath one would probably be unsurvivable. With the uncertainty surrounding this problem and the destructive nature of these avalanches, don't linger in areas where these large avalanches can run from above. This problem may stick around until freezing levels return to seasonal norms.

    (1/6/2022)

    A snow profile at 3000' at Snoqualmie Pass. Note the pooling water well below the surface. This could result in wet slab avalanches. 

    Photo: Alyssa Young

Avalanche Discussion

Over the last two days, most weather stations have sustained above freezing temperatures, and an avalanche professional at Mission Ridge saw moist snow grains to the ground. Also, large avalanches are still occurring in the Wenatchee mountains surrounding Leavenworth. This weather pattern is not our typical situation where we get a deep freeze after substantial snow and rain. The sustained warm temperatures will mean the snowpack will be slower to stabilize, and water will continue to move through the snow and pool on crusts and weak layers. On Wednesday and Thursday, NWAC forecasters observed large avalanches off Wedge Mountain and Icicle Ridge in Leavenworth.  Natural wet loose avalanches blocked Highway 2 in Tumwater Canyon on Thursday. Other than continued reports of isolated large to very large avalanches, we have little information on the snowpack since the Jan 5-8th storm. This leads to a lot of uncertainty with our forecast. It will be essential to assess snow conditions as you travel and enter new terrain slowly. 

Before and during this storm, large and very large avalanches ran naturally and were triggered by explosives on various deeply buried weak layers. The more recent layers consisted of large stellars, facets, and surface hoar from 1/2 and 12/29. A decomposing crust from the Solstice was the bed surface for some slides at Mission Ridge. An even deeper crust from Early December showed propagation potential on high elevation, shaded slopes in the Icicle drainage. These layers are likely buried 3 to 8ft deep and could still be capable of producing avalanches.

Many great Observations have come in from the area. Thanks, and keep them coming as we unravel the saga of the ongoing avalanche activity. 

 

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