Bollettino valanghe

West Slopes South

Northwest Avalanche Center
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Pericolo valanghe

Wed
Alta quota
3 · Marcato
Limite del bosco
2 · Moderato
Sotto il limite
2 · Moderato
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Non aggiornato — questo bollettino è scaduto 6 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

Give the snowpack time to adjust to the large amount of water we just received. Make conservative terrain choices on Tuesday and be aware of wind-drifted piles of snow where you could trigger an avalanche more easily. If you ascend above the previous rain/snow line, conditions will potentially be much more dangerous.

Problemi valanghivi

  • Wind Slabs

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

    The wind has been significant on Monday, with some NWAC weather stations in the zone recording gusts of 90mph. With a quick shot of snow and some moderate winds set to impact the zone on Monday night, we’ll start to turn the page on the rain and make Wind Slab as our primary focus for Tuesday. Look for these slabs on leeward slopes, at the base of cliffs, or on the sides of gullies in any part of the zone that receives more than a few inches of new snow. Areas that are above the previous rain/snow line will have pre-existing Wind Slabs that could be thickened on Tuesday. These slabs will be much larger and more dangerous than any new slabs formed below the previous rain/snow line. Taking note of freshly built cornices, textured snow surfaces, or pillow-like piles of snow could help you determine where these slabs may exist. If you experience clues of unstable snow such as shooting cracks or whumpfing collapses as you travel, or feel hardened snow that seems hollow below your feet, steer around slopes greater than 35 degrees.

    (12/20/2020) Shooting cracks were observed on Sunday in the White Pass area showing that instability still exists in the upper snowpack and there is slab potential.

  • Wet Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Unlikely
    Dimensione
    2

    Although unlikely at this point, we’re going to continue to be concerned about Wet Slab avalanches for another day in the West South. It can take some time for water to percolate through the snowpack and weaken the bonds between snow crystals, releasing large natural avalanches, so let’s give the snowpack some more time. Since wet avalanches are not well understood and the timing of wet avalanches is very difficult to predict, they can act in surprising ways. Minimize your exposure by choosing safe travel routes, staying off slopes over 35 degrees, and being aware of the terrain above you at all times. 

    (12/21/2020) This Wet Slab avalanche at Paradise connected terrain features for over 200 yards in width with a crown depth between 1 and 2 feet.

Avalanche Discussion

We are coming out of some major Wet Slab avalanche cycles across the zone which saw slides estimated to be up to size D2.5 with 3-foot crowns. The first cycle observed was on Sunday at Crystal where multiple D2 avalanches were found to have run on Saturday night around the backcountry. Sunday also brought word from NWAC observers that there were multiple slides up to D2 at Paradise. On Monday, NWAC team members were at Paradise and found that the cycle was quite large, with crowns that connected terrain features and propagated long distances. Remember that the best indication of avalanche potential is recent avalanches, and we just had a lot of them. Although the forecast calls for cooling temperatures which should generally help to lessen the avalanche danger, you should still ease into terrain carefully and make conservative decisions. Elevations above the previous rain/snow line have not been observed and there is uncertainty about how sensitive the snow will be. What we do know is that the slabs will be thicker and possibly more reactive, with potentially more dangerous avalanche conditions. When you have uncertainty, you should dial back your terrain choices.

During the ongoing Covid-19 pandemic, continue to follow the latest guidance from local, state, and federal health officials. Avoid unnecessary risks that could impact first responders and stress medical resources.  Wear a mask when appropriate, practice social distancing, and consider recreating closer to home.

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