Bollettino valanghe

West Slopes North

Northwest Avalanche Center
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Pericolo valanghe

Tue
Alta quota
3 · Marcato
Limite del bosco
2 · Moderato
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

There's a consensus amongst everyone that the new snow layer is deeeep. We just keep getting more and more snow, and you can trigger avalanches that might be around a foot deep, or possibly deeper, some of which may be in wind-affected areas and others may just be light and fluffy new snow, so avoid all steep slopes. Deep, unconsolidated snow, tree wells and other mysterious holes in the snow may be the most dangerous part of your outing on Monday. 

Problemi valanghivi

  • Storm Slabs

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

    On Sunday natural and human-triggered avalanches were reported in the Baker backcountry. Some avalanches were 3-6 inch wind slabs, others were reported as a little deeper, up to about a foot. Some were wind slabs while others were non wind-affected storm slabs. One avalanche on a north-facing slope at about 5000ft was reported as failing 8-12 inches deep and propagating a couple hundred feet, in Little Alaska. It was reported as a D1.5 and ran almost to the the bottom of Bagley Basin.

    We suspect that you'll see similar conditions on Monday, although we're forecast to get another .6 inches of water or so from Sunday night through to the end of the day Monday. Of note about this relatively meager .6 inches of water is that with these cold temperatures we suspect that we could get a foot, possibly more, of very low density snow on top of all the fluff that already exists. Very unusual slab/loose avalanches may run in this snow. They will probably mainly be small, but some large avalanches may occur.

    Avoid slopes steeper than 35° on Monday. If you see natural avalanches running, avoid terrain beneath steep slopes as well.

    (3/3/2024)

    A skier triggered slab avalanche on a west-facing slope above Iceberg Lake. The pocket propagated both directions and the debris ended up in old growth trees. "A good old fashioned terrain trap" according to the photographer. 

    Photo: Brian Barkley

  • Loose Dry

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    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 you enter any steep terrain. Loose avalanche may behave unusually in this deep, light layer of snow, they may start as loose but then might trigger a slab avalanche further down. 

    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.

    (4/2/2023)

    Example photo: These wild dry loose avalanches might happen on Monday. 

    Photo: Jason Speer

Avalanche Discussion

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.

The last storm left behind crowns and debris from natural avalanches on many north-facing, upper elevation start zones around the Baker backcountry. Similar avalanche activity is suspected from other parts of the forecast zone, but observations are lacking. Layers of weak faceted snow that failed under extreme loading during the latest storm are the likely culprit, close to the Early February Crust. 

These layers are now buried about 6 or more feet beneath the surface, so we suspect it's highly unlikely that a human will trigger an avalanche on this layer. In addition to this, several natural avalanches, and explosives-triggered ones occurred on this layer midway through the storm, during the avalanche warning on Wednesday. We believe most areas where this weakness existed already avalanched, and don't particularly expect any new ones to occur now. Although very unlikely an very large avalanche occurring on this layer isn't completely out of the question.

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. If any avalanche occurred here, 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 an avalanche 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.

In wind-sheltered areas, the snow that has fallen since the 24th is generally right-side up, with inter-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' or more over the same crust.

Regioni coperte