Lawinenlagebericht

East Slopes Central

Northwest Avalanche Center
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Lawinengefahr

Tue
Hochgebirge
3 · Erheblich
Waldgrenze
3 · Erheblich
Unterhalb
2 · Mässig
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Veraltet — dieser Lagebericht ist 4 years ago abgelaufen. Du siehst vergangene Verhältnisse, nicht den aktuellen Bericht.

Kernpunkte

Dangerous avalanche conditions will develop as new snow and wind combine to create reactive pockets of wind-drifted snow. Look for these pockets to develop along ridgelines, under cornices, and on wind-exposed open slopes. Consider the consequence of one of these slabs stepping down to older, buried weak layers and producing a bigger and more surprising avalanche.

Lawinenprobleme

  • Wind Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Likely
    Größe
    1–2

    West winds will be at work drifting new snow into reactive slabs. These slabs will build in size and distribution across the terrain as new snow piles up. More snow is forecasted for the crest, so expect these slabs to be larger on the western parts of the zone. 

    Use visual clues such as blowing snow or fresh drifts to help you identify slopes of concern. Look for these pillow-like slabs forming on the leeward side of ridges, under cornices, and peppered in the alpine. High wind speeds may push these slabs further down slope than usual.

    Any triggered wind slab could step down into older buried weak layers. This scenario would produce a much larger, surprising avalanche that could be unsurvivable. So the best policy is to simply limit your exposure to wind-drifted slopes greater than 35 degrees.  Don’t ignore obvious signs of instability such as cracks shooting out from your skis/sled or if you notice hard over soft layering.

    (1/9/2023)

    Wind slabs like this could fail on steep slopes with a human-trigger on Monday. 

    Photo: Irene Henninger

Avalanche Discussion

Monday is shaping up to be a stormy day for the Cascade Crest. Precipitation amounts should taper further east, with the Wenatchee Mountains receiving miniscule amounts. However, if you do plan on traveling in western parts of the East-Central, keep an eye out for storm instabilities developing during the afternoon hours. New snow will likely bond well to the moist surfaces, but be ready to adjust your travel plans if you notice something different, like new snow sliding easily or notice shooting cracks in the fresh snow.

On Sunday, observers reported moist snow surfaces up to 7000 ft and saturated surface hoar even on northerly aspects.  Saturday, I traveled near Lake Wenatchee to investigate how the new snow from 2/8 is bonding with the old snow surface. Above 5000 ft, I found approximately 12 inches of new snow sitting on the new/old snow interface. Snowpack tests produced sudden planar results, but didn’t show the ability to propagate with larger columns. However, I did get propagation on a layer of weak, sugary snow above the MLK crust about 17 inches below the snow surface. Look at the photo gallery for more information. 

Observations from the near-by Stevens Pass zone continue to trickle in of large avalanches being triggered and some releasing naturally.  On Saturday a report came in of a rider triggering a slab avalanche failing on the February 3rd interface on a ENE aspect at 5400 ft (observation). Another observation came in on Sunday evening of a widely propagating avalanche on the south aspect of Jove Peak ( observation here). These avalanche occurrences are worth noting if you plan on traveling along the western edges of the East-Central. 

Last week, observers reported whumphing collapses and avalanches being triggered on the new/old snow interface.This layer consists of small grained faceted snow and is about 1-1.5 feet deep. 

Common landmarks deeper in the snowpack are the MLK crust and the Christmas Crust, buried 1.5-2.5 deep and 3-4ft, respectively. The recent cold weather weakened the snow above and below the MLK crust into weak, faceted grains, creating a weak structure that we're still watching. 

In the eastern Wenatchee Mountains, two prominent layers of buried surface hoar exist. The lower layer of surface hoar, buried on January 4th, is still producing propagating test results, despite being below the MLK crust. A layer of surface hoar, buried on January 18th may produce avalanches with the newer snow load on top. So keep it in your mind, and choose conservative terrain if traveling in the Wenatchee Mountains. 

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