Bollettino valanghe

West Slopes Central

Northwest Avalanche Center
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Pericolo valanghe

Mon
Alta quota
3 · Marcato
Limite del bosco
2 · Moderato
Sotto il limite
2 · Moderato
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In sintesi

You can trigger an avalanche on steep slopes holding slabs of wind-drifted snow. Identify and avoid steep slopes with recent wind-loading. Deep, unconsolidated snow and tree wells might be the greatest danger you encounter on Sunday. 

Problemi valanghivi

  • Wind Slabs

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

    Another day of gusty winds made for another day of wind transport and slab formation. Wind speeds and fresh slab formation should be lesser on Sunday, so you will mostly deal with slightly stale, day-old slabs. Cornices grew larger during the last few rounds of storms and could be quite fragile - give them plenty of room when traveling along ridgelines.

    Look for variations in snow appearance, texture, and stiffness to determine which slopes are most likely to hold wind slab. Stomping on tiny cornices and other features shaped or loaded by wind can help you determine reactivity. If you observe active wind transport, be ready to find more reactive slabs. When in doubt, use a lower-angled line to navigate around wind-loaded slopes.

    (3/2/2024)

    Skier-triggered slab avalanche in wind-drifted snow. Southwest aspect of Herman/West North at about 5100'.

    (SS-AS-D1-S)

    Photo: Kameron Decker Harris

  • Loose Dry

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Unlikely
    Dimensione
    1–1.5

    Cold, light snow at the surface is easy to push around and get moving in steep terrain. While mostly small, loose snow avalanches can pick you up and carry you downhill into a tree, gully, or other hazards. Be aware of how much snow is moving with you if descending steep terrain.

    The sun hasn’t had much of an effect the last few days, but when it does eventually come out for real and warm up the snow surface, be ready for a round of loose snow avalanches. Look for rollerballs and small loose snow avalanches if the sun makes and appearance. Warming can also form a reactive slab from loose dry snow at the surface.

    (2/26/2024)

    Dry loose avalanches in non wind-affected snow.

    Photo: Zoë Vernon

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.

The setup for deep snow immersion or disappearing into a tree well is currently about as dangerous as it gets.  Many feet of light and unconsolidated snow combined with previously low snow cover have created countless traps that seem fully covered at the surface.  Avoid traveling close to trees, have a partner, and keep them in sight at all times.  A tree well was responsible for a fatal accident in backcountry terrain on Friday.

Windy conditions, blowing snow, and active wind transport were the common themes up and down the west side of the Cascades on Saturday. While most human-triggered avalanches were D1 in size, they were found on a variety of aspects and quite reactive. Other signs of instability consisted of fresh wind-drifted features easily cracking and failing 8-12” deep and some small loose dry avalanches triggered on shorter, steep slopes. While the snow is still deep, it’s settled enough to make for easier travel going both up and down the hill.

The last storm left behind deep crowns and debris from natural avalanches in neighboring zones. Layers of weak faceted snow that failed under extreme loading during the latest storm are the likely culprit. Avalanche forecast zones to the south (West South), the entire east slopes of the Cascades, and also to the north (Canada) have legitimate persistent slab problems with continued avalanche activity related to similar layering.

Now buried under several feet of new snow, it’s unlikely - but not impossible - a person could trigger a deeper avalanche. The best chance would be on northerly aspects at upper elevations, and where the snowpack is also shallower over the Early February Crust. Locations farther east in the zone may have a better-developed weak layer and less snow over the crust. 

Don’t ignore signs of instability like whumping or shooting cracks - they are the best sign that you could trigger one of these in steep terrain. Bigger loads like a falling cornice, smaller avalanche or group of people might trigger one of these larger avalanches where a single person would not.

 

 

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