Lawinenlagebericht

East Slopes North

Northwest Avalanche Center
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Lawinengefahr

Fri
Hochgebirge
3 · Erheblich
Waldgrenze
3 · Erheblich
Unterhalb
2 · Mässig
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Kernpunkte

As we add more snow to a sensitive snowpack dangerous avalanche conditions are likely to follow.  Triggering a shallow slab avalanche could result in a larger avalanche in older snow that breaks widely around terrain features. Thursday is a good day to avoid all large open slopes steeper than 30 degrees at mid and upper elevations.  

Lawinenprobleme

  • Storm Slabs

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

    With 6-10 inches of snow in the forecast through Thursday, you can trigger a storm slab avalanche on convex rolls or very steep terrain.  Look for shooting cracks as you travel and use small test slopes to test the stability of the new snow. In areas where firmer wind-affected snow is present, look for new cornice formations and wind rolls to ascertain which slopes below ridgelines may have been recently loaded.  While a new snow avalanche could take you for a ride, think about the consequences if one steps down to deeper layers. 

    (12/16/2020) Shooting cracks give you a clear signal of slab avalanche potential. Photo: Dirty Face Mt.

  • Persistent Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    2

    While you are more likely to find a shallow storm slab on Thursday, it's the lurking, larger persistent slab avalanche that grabs your attention and makes you think twice about your terrain choices.  Persistent slab avalanches are dangerous and can catch even the most experienced backcountry travelers by surprise.  They can break widely around terrain features and be triggered from lower angle slopes. As the snow piles up, the potential for larger avalanches that break down to a facet-crust combo increases. 

    The persistent slab structure had already been identified in the neighboring East Central zone.  Now with fresh reports from observers in the Washington Pass area, we're adding a persistent slab ahead of a relatively significant loading event. On Wednesday the aforementioned observers experienced whumfping collapses, signs that a  persistent slab problem may be primed to wake up in this zone.  Dig down to look for weak sugary snow above a firm crust in the near and above treeline elevation bands.  On Wednesday the depth to that weak layer was 8-12" and could double by the end of Thursday.

    Keep your terrain selection conservative Thursday and avoid open slopes above 30 degrees at mid and upper elevations.  

Avalanche Discussion

The active weather pattern continues this week as we incrementally load the snowpack along the east slopes of the Cascades with each passing storm. 

A thick freezing rain crust from December 9th can be found below 5,000ft and east of Washington Pass.  6" or less of new snow has bonded poorly to the crust.  In these areas, the slick crust creates challenging traveling conditions.  On Wednesday observers noted near the Pass proper and above 5500' a rougher melt-freeze crust with up to 12" (30cm) of snow on top.  Natural wind slabs had released during the previous storm below ridgelines and cliff bands. 

The snowpack remains shallow at lower elevations, and early season hazards such as downed trees, rocks and creeks are plentiful. At lower elevations and steep slopes, dust on crust conditions may make for icy and/or tricky travel.

During the ongoing Covid-19 pandemic, continue to follow the latest guidance from local, state, and federal health officials. Avoid unnecessary risks that could impact first responders and stress medical resources. Wear a mask when appropriate, practice social distancing, and consider recreating closer to home.

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