Bollettino valanghe

West Slopes Central

Northwest Avalanche Center
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Pericolo valanghe

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

Wet snow avalanches that are large and unpredictable are still a concern, although we aren't quite sure how reactive they remain.  Be wary of traveling on or under steep slopes in areas where you see glide cracks or large overhanging cornices above you, as these features could fail while temperatures remain warm and rain continues. Tuesday's warm, wet weather could cool enough later in the day that you might see snow at higher elevations and you could trigger a wind slab avalanche if snow drifts grow deep enough.

Problemi valanghivi

  • Glide Cracks

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    1.5–2.5

    Glide avalanches characteristically fail at the ground, often in areas where smooth rock slabs or low shrubs are lubricated by liquid water. You may see a glide crack, usually near the top or middle of a steep slope, as an indicator that the slope below could release as an avalanche soon. Back in my early ski patrol days I saw a large glide crack at the ski area one morning. I went to check it out on my next lap, and by the time I got there I only found a large avalanche debris pile and a slick, grassy bed surface beneath. I'm glad that the avalanche hadn't occurred while I was investigating it. Now I stay far away from glide cracks and areas beneath them.  On the other hand, some glide cracks can sit around for days or weeks but change minimally. It's tough to tell whether a glide crack will release quickly or not at all. 

    As rain continues to fall and temperatures remain relatively warm, beneath one of these glide cracks, or a large, overhanging, cornice, is no place to be. Steer around steep slopes where you find these features. Avoid or travel quickly across the flats beneath glide cracks and cornices. 

    A glide avalanche which occurred on a grassy slope near Highway 20 on a previous year. Photo: Brian Doolittle

  • Wind Slabs

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

    A lot of water is coming in the next 24 hours. Hopefully we're not being too optimistic by saying that temperatures will be dropping and it could end as snow, especially at higher elevations. Winds will be strong enough to redistribute new snow into reactive slabs.  We're not quite sure how well snow will stick to the old, previously moist surface. In some areas it may stay in place, while in other locations, especially where wind redistributed the snow into thicker, heavier slabs, the snow could slide near the old snow surface. 

    You can probably identify where wind deposited fresh new slabs. Drifts could be speckled across an unusual rain-sculpted landscape, filling in gullies, or sitting in pillows on leeward sides of features and ridgelines. Depending on how much snow and wind we get, avalanches could stay inconsequential in size, or they could grow so large that if you trigger one it could carry and bury you.

    It's up to you to determine how deep the slabs are, and identify whether the snow bonds well to the underlying layers. You can quickly isolate a column of new snow above the old snow layer with your hand and see if any new layers easily pop off or if they stay stuck to the underlying snow.  Long, shooting cracks indicate the snow layer could avalanche on a steep slope. If your steps cause long, shooting cracks or you find layers that aren't bonded well to the underlying snow in large enough patches, avoid slopes greater than 35 degrees. If the slab is only a few inches thick it's probably not enough to cause a problem, but when it starts getting a bit deeper that's when enough snow could be present to take you for a scary ride .

    Pockets of wind slabs which develop as the day progresses could react to a human trigger. Photo: Public Ob

Avalanche Discussion

Snow depths are shallower at lower elevations, as I found during my trip to Highway 20 just north of the West Central zone on Monday and when I went to Lake 22 Saturday. Some below treeline spots might not hold enough snow to avalanche. In other areas, avalanches could be smaller. However, if you’re on a lower elevation adventure in or near mountains, be aware of crossing gullies that could connect with a large avalanche path far above you. This was notable during my Hwy 20 visit past Newhalem with a WSDOT team, as the road which had been closed before the warming event had a few large avalanches running from above treeline elevations down tight gullies to the low elevation road. 

Warm wet weather arrived early Christmas Eve after a week of cold temperatures and feet of dry, low density snow fell. When temperatures first warmed and rain began falling a large avalanche cycle probably occurred. I saw evidence of a few early warming event avalanches when I investigated Hwy 20 near Newhalem Monday. The weather has been so wild since Friday that almost no one has made it into the mountains, and we aren't quite sure what's going on out there. Precipitation isn't letting up until Wednesday, when temperatures will finally drop to more seasonal norms. A glide avalanche cycle could be continuing until we have had a good freeze on the snowpack, although we aren't really sure. Glide avalanches are scary and unpredictable. It's tough to tell when they'll fail. Until we have more information and temperatures cool, continue to make conservative decisions in the backcountry.

Travel will be challenging, with soft, punchy snow. You can expect to find flooding and an overall wet day. Surfaces may freeze and become slick at upper elevations. If you get out, even on a low elevation hike, let us know how much snow there was and if you saw any recent avalanches. You can submit an observation HERE. 

 

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