Bollettino valanghe

West Slopes South

Northwest Avalanche Center
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Pericolo valanghe

Wed
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
1 · Debole
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In sintesi

If you are planning on taking advantage of the calm before the storm to venture toward upper elevations on Tuesday, don’t be surprised to find a lingering Wind Slab. These slabs could break in surprising ways, so if you notice textured snow surfaces or firm, hollow-sounding snow, then head for lower angled slopes.

Problemi valanghivi

  • Wind Slabs

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

    A large Wind Slab avalanche was observed in the Crystal backcountry on Sunday afternoon along with smaller human triggered slabs. In the neighboring Snoqualmie Pass zone, there were multiple human triggered avalanches on Monday. Receiving reports of recent avalanches reminds us that the snowpack is still adjusting to the previous wind event and that’s enough for us to continue talking about Wind Slabs for Tuesday. We believe the largest and more unpredictable slabs to be on NE-N-NW aspects, but since we experienced a variety of wind directions and some unusual loading patterns, you should look for pockets of wind affected snow on all aspects. You are more likely to find these slabs as you ascend in elevation, with the possibility of them being large at higher elevations. You can look for smooth pillow-like piles of snow or textured surfaces to help you clue into wind deposited areas. You can then use small test slopes to test the bonding and reactivity of these slabs. If you encounter firm, hollow-sounding snow, you could be dealing with more stubborn hard slabs that have been breaking in surprising ways throughout the region and you should head for lower angled slopes. Windblown snow often accumulates on the sides of gullies, the base of cliffs, or on convex rollovers. These features will be more likely to produce avalanches.

    (12/28/2020) This large avalanche in the Crystal Backcountry was 2-3 feet deep and 200+ feet wide. It ran across 3 cross-loaded gullies and had an unknown trigger. [NE side of Crown Point ~6460'. Photo: Seth Waterfall]

Avalanche Discussion

The snowpack around the West South contains an average of 20-35cm of snow over a prominent crust (12/21). Some areas have been stripped down to the crust by the wind, while other areas have wind drifted pockets as deep as 60-70cm. Avalanche activity should continue to be confined to the snow above the crust, with weak snow grains sitting above the crust possibly causing a point of failure for larger avalanches. Crystal Pro Patrol recently had slabs release on these weak grains, breaking 1.5-2.5 feet deep. On Sunday, a large avalanche was found in the Crystal backcountry to have propagated 200+ feet and contained a 2-3 foot crown. The trigger for this slide is unknown, but we suspect that this slide also ran on the 12/21 crust. Throughout the region, similar slides have been breaking in surprising ways, sometimes after multiple people have safely traveled over them, or sometimes through remote triggering. This unpredictability leads to a great deal of uncertainty about when and how these slabs will pose a problem, but most have generally been found on NE-N-NW aspects which have been wind-loaded. With a significant storm set to impact the area on Wednesday, look for an increase in hazard and further stress to be applied to our current snowpack setup.

The 12/21 crust is very firm and travel conditions can be difficult because of it. Allow yourself extra time and look out for open creeks and other early season conditions at lower elevations.

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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