East Slopes South

Dangerous to very dangerous avalanche conditions are expected as new snow is increasing the chances of triggering persistent slab avalanches 3ft deep. The new snow is not bonding well to previous weak surfaces as it is, and expect to be able to trigger avalanches on all steep open slopes as you gain elevation. Avoid going into, or underneath steep open slopes at upper elevations, and steep terrain at any elevation if you find more than 14" of new snow and signs of instability such as shooting cracks. 

Preliminary avalanche incident information Monday February 8th, 2021: Two snow bike riders were caught and buried by a very large avalanche in the mountains west of Salmon la Sac Sno-Park along Cle Elum Lake. One snow biker was partially buried and was able to dig himself out. The other rider was fully buried and killed by the avalanche. The avalanche occurred on a northeast aspect at 4400 ft in the Knox Creek drainage. This terrain lies in NWAC’s East Central forecast zone. Avalanche classification: HS-AV-R3-D3-O.  See the short video in the media gallery below.

All of us at NWAC want to extend our condolences to family, friends and the local community following this tragic event.  

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Up to 2ft of new snow has fallen in the zone since the 11th. New snow will continue to slowly pile up through Sunday, before heavy snowfall returns on Sunday night into Monday. Previous snow surfaces are suspected to be a mix of weak, and perhaps faceted grain types. An observer at White Pass found widely propagating storm slabs that were acting in surprising ways (see below), as they failed over these weak snow surfaces. Expect these storm and wind slabs to be easily triggered on steep slopes, and where the wind has thickened the snow on Sunday. 

With this added loading we are becoming more concerned about deeper persistent weak layers in the East South zone.  Large and deadly persistent slab avalanches have occurred in neighboring zones (East Central and West South), and the new storm load is increasing the chances of triggering one of these monsters. Continue to limit your exposure to open steep slopes, and large avalanche paths.  Triggering a smaller avalanche or cornice fall could result in a very wide avalanche about 3ft deep. Persistent slabs can break widely and wrap around terrain features. They can be triggered from connected slopes below. Don't try to manage this problem.  Give yourself a healthy buffer and stick to lower angled terrain at mid and lower elevations that are not exposed to bigger slopes from above.

If you're out in East South, help improve this bulletin by submitting an observation. 

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.