Bollettino valanghe

East Slopes South

Northwest Avalanche Center
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Pericolo valanghe

Mon
Alta quota
3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
2 · Moderato
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Non aggiornato — questo bollettino è scaduto 2 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

The snowpack remains sketchy out there despite the break in weather. You can still trigger a large, unsurvivable avalanche that breaks 2-4 ft deep on weak snow above a crust. Continue to avoid being on and under large, open slopes greater than 30 degrees. 

Problemi valanghivi

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    1–2

    Winds will continue to move new snow into stiff, cohesive slabs on leeward features. On Saturday, observers around the region reported gusty winds and plumes along ridgetops. You’ll typically find these wind slabs downwind side of ridges,below cornices, and under rock and cliff bands. Use visual clues such as blowing snow, sharp cornices, and textured surfaces to help you identify wind loaded slopes.  These slabs will often appear as rounded, pillow-like, and sometimes sound hollow. Any triggered wind slab has the potential to step down to older buried weak layer and become a much larger, unsurvivable avalanche. So continue to avoid steep wind loaded features until our weak snow has healed up.

    (2/16/2024)

    Visual observations help you anticipate wind loaded slopes.

    Photo: Dallas Glass

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    2–3

    Weak, faceted snow over the Early February Crust created a tricky and dangerous persistent slab problem. A fatal avalanche accident near Darland Mountain on Friday failed 2-4 ft deep on this deeply buried persistent weak layer (preliminary statement in discussion).  After the recent storms, a thicker slab exists over this weak layer, so avalanches will likely be much larger. A smaller avalanche could also step down to this layer. You can trigger a persistent slab avalanche from low-angle terrain below or adjacent to steep slopes, and they may propagate widely across terrain. You may or may not observe signs of instability, like collapsing, before triggering an avalanche, and it may not be the first person on the slope to trigger it. 

    Avoid traveling on or under slopes over 30 degrees. Give steep open slopes wide safety margins. These are not conditions where you can manage the hazard on a small feature scale, as large slopes can fracture at once, running through lower-angle benches and small features. Stay off of and out from underneath steep slopes at elevations above approximately 4500ft, where 1-3ft of new snow has accumulated since 2/24. Heavy rain likely created a thick, slippery crust at lower elevations and will limit avalanche potential.

    (3/1/2024)

    You can trigger similar avalanches on Sunday.

    This remotely triggered avalanche occurred on a North aspect at 6300 ft near Darland Mtn on Friday, March 1st.

Avalanche Discussion

Preliminary Report: An avalanche accident occurred on Friday, March 1, near Darland Mt in the Ahtanum Meadows area. Two snowmobilers were involved in the slide. One rider was fully buried and killed. The avalanche occurred around 6600ft in a generally east-facing bowl. NWAC staff will visit the accident site on Saturday. Our deepest condolences to the family, friends, and community.

Observers across the east-south and region have reported numerous large avalanches failing on old snow 2-4 ft below the surface. In addition to the fatal avalanche accident on Darland Mt on March 1st, another large avalanche on an adjacent slope was remotely triggered by a group of snowmobilers. This widely propagating avalanche occurred on a north aspect at 6300 ft. You can check out the observation here.  NWAC forecasters visiting the accident site also reported this separate large avalanche (avalanche observation).  These all likely failed on the Early February weak layer. 

This pattern of persistent slab problems can be incredibly challenging for backcountry decision-making. It takes extremely conservative terrain management and patience. This winter's lower-than-average snowfall and warmer-than-average temperatures contribute to a shallow snowpack prone to developing these tricky weak layers. The issue is especially apparent in the eastern Cascades, which, on a typical year, is already a bit shallower and weaker than areas west of the crest. So, if you're venturing into these eastern zones this winter, be prepared to take a step back in your typical terrain selection and understanding of the snowpack. It's easy to be surprised in these conditions, so with the increased complexity of the snowpack, choose low-angle terrain to enjoy the fresh snow. 

If the sun comes out to stay for a while in the afternoon, you may see some small, wet loose avalanches, rollerballs, and pinwheels. 

Your avalanche, snowpack, or weather observations are extremely valuable to the avalanche community. Help create a more accurate avalanche forecast by submitting your observations here. 

 

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