Bollettino valanghe

West Slopes North

Northwest Avalanche Center
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Pericolo valanghe

Sun
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

Keep your terrain choices conservative and avoid big, steep slopes, especially where you identify recently wind-drifted snow. Deep snow immersion is a real hazard. Travel with a partner and keep them in sight at all times. Expect challenging travel with difficult trail-breaking.

Problemi valanghivi

  • Wind Slabs

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

    Wind transport and natural wind slab avalanches were observed on Friday. With plenty of light snow on the ground and periods of moderate to strong wind, expect more of the same on Saturday. A shift in wind direction could change the loading pattern midday.

    Active loading, scoured and eroded snow surfaces, cornices, and other clues will show you which slopes have loaded up with wind-drifted snow. The best policy on Saturday will be to avoid steep terrain where you suspect the wind has formed stiffer, more cohesive slabs.

    (3/1/2024)

    Fresh slab avalanche in wind-loaded terrain on the Diamond. Natrually triggered, east aspect at 5100'. Signs of wind transport on slopes to the right and left of the avalanche.

    (SS-N-D2-S)

  • 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 uncohesive and 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.

    Also, expect sun breaks and periods of warming between snow showers over the next few days. The March sun is strong and can quickly warm up the snow surface despite cold temperatures. Look for rollerballs and small loose snow avalanches if the sun is out. Warming can also form a reactive slab from loose dry snow at the surface.

    (2/24/2023)

    Example of dry loose avalanches big enough to knock you down and take you for a short ride.

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.

Good visibility on Friday allowed for a look around the mountains, and the results were impressive. Deep, wide crowns from natural avalanches that released during the storm outlined most northerly facing, upper elevation start zones around the Baker BC. 

Layers of weak faceted snow that failed under extreme loading during the latest storm are the likely culprit. No human-triggered avalanches related to faceted snow or crust-facet combinations were reported in the last few days. But it’s also been difficult for people to get very far into the mountains.

Now buried under several feet of new snow, it’s unlikely - but not impossible - a person could trigger a similar 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.

In wind-sheltered areas, the snow that has fallen since the 24th is generally right-side up, with intra-storm layers showing little reactivity. A recent snowpit (photo) in the Baker BC showed nearly 5’ of new snow with over 6’ on top of the Early February Crust. Wind-loaded slopes representative of ridgeline start zones have 8' over the same crust.

 

 

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