Lawinenlagebericht

East Slopes Central

Northwest Avalanche Center
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Lawinengefahr

Sun
Hochgebirge
3 · Erheblich
Waldgrenze
3 · Erheblich
Unterhalb
3 · Erheblich
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Kernpunkte

While we are on a downward trend, there is still a complex snowpack with overlapping avalanche problems and the potential for very large avalanches to run significant distances. Avoid traveling on steep terrain where you find wet, heavy snow, and don't linger in the runout of very large avalanche paths, including creeks and gullies in valley bottoms. 

Lawinenprobleme

  • Wet Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Likely
    Größe
    2–3

    Wet slabs are notoriously hard to forecast. They sometimes release after peak precipitation with sustained warm temperatures. While we will see gradual cooling on Saturday, it won't be significant, and there will still be some lingering precipitation to keep this avalanche problem active. A layered snowpack with persistent weak layers and a thick crust from Christmas is a perfect setup for these destructive avalanches. While you will be more likely to trigger these in locations where you find heavy wet snow that you sink deeply into, there is still a possibility of wet slabs releasing naturally at higher elevations and funneling to valley bottoms in steep gullies and creek drainages. Use maps to identify steep alpine terrain with drainages that run to lower elevations. Avoid traveling on steep slopes where you may trigger one of these large avalanches, and don't pause in areas with exposure to steep open terrain above you, particularly steep rock slabs or cliffs. 

    You will likely see smaller wet loose avalanches at lower elevations where less new snow rests on the Christmas Crust. 

    (1/13/2023)

    This very large avalanche in Tumwater Canyon occurred sometime on Friday and is a perfect example of avalanches running in creek drainages to valley bottom. 

    Photo: Harlen Sheppard

  • Storm Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Likely
    Größe
    1.5–2.5

    While wet avalanches are the apparent problem seen from trailheads, above 5000-5500ft precipitation stayed as snow in most locations throughout the zone. Lingering high-elevation snow on Saturday will maintain the possibility of triggering sensitive storm slabs. Winds are also forecasted to increase, drifting any soft snow into deeper, more dangerous slabs. This heavier snow is falling on cold, low-density snow from earlier in the week and potentially deeply buried weak snow layers. Storm slabs may break in the new snow and be large in areas where the wind has drifted snow deeper. It is also important to note an observation of a layer of weak faceted snow buried deeply in the snowpack in alpine terrain before this storm. While we have no information from the upper elevations since this storm, there is potential for avalanches failing on these deeper weak layers and becoming very large. With this uncertainty, treat all higher elevation slopes as suspect. Travel on low-angle terrain sheltered from the wind, where you find new dry storm snow over 6 inches deep.  

    (12/20/2022)

    If you're seeing natural storm slabs like this below treeline, you already know conditions are touchy.

    Photo: Alexa Cathcart

Avalanche Discussion

The East Central zone has been in a sustained and stormy period for what feels like weeks. This storm pattern is still ongoing, and we will likely squeeze out 4-6 inches of additional snow at higher elevations with increasing winds. Lower elevations will continue to see rain with a very gradual cooling trend. Before this storm, persistent slab avalanches 1-2 feet deep in the Wenatchee Mountains were widespread on N-E aspects, failing on a layer of buried surface hoar. Rain has likely destroyed this layer over the last 48hrs. However, we are still suspicious about reports of skier triggered wind slabs failing on unknown layers at higher elevations on northerly aspects. Also, observations of weak faceted grains with unstable snowpack test results and sensitive storm snow instabilities came in from the Icicle Creek Area. At the same time, some other observations and locations found a relatively stable snowpack. This spatially variable snowpack setup leads to significant uncertainty in slope stability in alpine terrain. Anytime there is increased uncertainty, larger margins of safety are necessary to account for unknown conditions. 

Thursday's storm buried these persistent weak layers deeper in the snowpack at higher elevations, and rain saturated the lower elevations. As a result, a widespread natural cycle with wet avalanches up to D3 and smaller storm/wind slabs occurred on Thursday and into Friday. Friday morning, the WSDOT NCR avalanche crew reported multiple D2 wet slab avalanches, with a couple up to size D3. The peak of instability is likely behind us, but with continued warm temperatures and lingering precipitation, we may continue to see occasional very large wet slab avalanches. So enjoy the wet stormy weather from low-angle terrain, far from the runouts of large avalanche paths, while we wait for precipitation to end and temperatures to cool. 

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