Bollettino valanghe

West Slopes Central

Northwest Avalanche Center
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Pericolo valanghe

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

An incoming storm will result in new storm snow avalanches that could be up to a foot deep, or more in wind-loaded areas. Danger will increase throughout the day as more snow falls. Avoid steep slopes, especially if you identify obvious clues like whumphing or shooting cracks, and consider avoiding travel beneath large steep slopes if you see natural avalanches. 

Problemi valanghivi

  • Storm Slabs

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

    It's likely that you can trigger avalanches in the new storm snow. Expect avalanches to fail as deep as the new snow layer, or possibly deeper, under wind slabs formed in recent days that you won't be able to see under the new snow. 

    An irregular patchwork of old snow layers, from wind slabs and firmer surfaces, crusts, or weak, faceted grains exist beneath the new snow that falls, so expect reactivity to vary even on the same slope. At the start of the day snowfall amounts will probably just be enough for an uptick in triggering avalanches, but expect more activity as the day progresses and more snow falls. 

    Slabs will likely be more reactive in wind-loaded spots. New snow depths are shallow enough that you can do simple tests to judge the reactivity of the new snow layer. Search for obvious clues like whumphing or long, shooting cracks as clear signs to avoid steep slopes. In general, avoid traveling on slopes greater than 30° where more than a few inches of new snow exists. If you see natural avalanches, consider avoiding terrain beneath large slopes as well. 

    Example photo: Storm slabs, similar to this one, are likely to fail with a human trigger on Sunday. Natural avalanches are possible. Depths will increase, and we suspect reactivity as well, throughout the day. 

Avalanche Discussion

We're uncertain if an additional load of snow will awaken the Persistent Slab avalanche problem that was listed last week. The last known avalanche to occur on the weak snow that's buried about 2-4ft below the surface was on February 2. Forecasts are calling for about 6 inches overnight and another 6 or so inches during the day, equating to around an inch of water.

If we were getting several inches of water, especially rain, we'd be much more alarmed about avalanches stepping down or failing on the deeper persistent layers, but given the relatively meager new loading amounts, we don't believe we're quite there with seeing an uptick of avalanches on this layer, although it's not out of the question. Be mindful that mid and upper elevation slopes on the northerly half of the compass are where any deeper avalanches, probably unsurvivable, would likely occur.

Snow levels are expected to rise to 3500ft on Sunday. Moist or wet snow at lower elevations could run as small, wet loose avalanches, naturally or with a human trigger. If you see rollerballs or natural avalanches running on steep slopes then avoid similar steep terrain and areas beneath those slopes. 

Under the new snow layer, light, dry snow existed on sheltered, shady slopes. Crusts are on steep, sunny slopes. Faceting, or weakening of the snow surface has happened in the last week, in addition to surface hoar development. It's safe to assume that many windward slopes had much of the weak snow at the surface scattered or destroyed by the strong wind in previous days. 

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