Bollettino valanghe

West Slopes South

Northwest Avalanche Center
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UPDATE: Increased avalanche danger below treeline. Colder than expected overnight temps allowed more snow than anticipated to accumulate at lower elevations.

A break in the storms Sunday may tempt you to venture into steeper terrain. However, a parade of winter storms formed several potential weak layers in the upper snowpack over the past few days. Stay off of open slopes greater than 35 degrees and give the snow time to adjust to these new loads.

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    The next in a series of winter storms should impact the West-South zone Saturday night forming new slabs. With relatively warm temperatures and heavy precipitation rates expected overnight, don’t be surprised if you see evidence of a natural avalanche cycle. New crowns and piles of debris could hide under a few inches of soft dry snow. Even though we expect the bulk of the natural avalanche activity to occur Saturday night, these new weak layers can still fail under your weight. Steer around open slopes greater than 35 degrees and allow the snowpack time to gain strength. You can use hand-pits and small slope tests to hunt for weak layers in the new snow and see how they change over the course of the day.

    In locations that received significant snowfall over the past few days (Paradise, Chinook Pass, Mt St Helens), these simple tests may not highlight the true dangers that could lurk in the snow. Several potential weak layers exist in the upper snowpack. Any avalanche failing on these deeper layers or entraining significant amounts of snow could grow large and deadly. Be particularly cautious in the areas with deeper storm totals.  

    With cooling temperatures, you may find several inches of light unconsolidated snow at the surface. This may produce loose dry avalanches in steep and even treed terrain. While these sluffs can seem harmless, don’t let them catch you off guard and knock you into a terrain trap.

    (12/31/2020) This large avalanche outside of the White Pass ski area ran out into the flats below the path. Gunsight Bowl. NE-E 6300' HS-ACu-D2.5-R3-I

Avalanche Discussion

The West-South zone truly demonstrated its diversity during the recent storms. As of Saturday afternoon Paradise receive more than 5.5” of precipitation since 12/29. White Pass and Crystal both received less than half of that amount. Similarly, storm totals since the 29th show a wide range in disparity. (Crystal 12-18”, Paradise: 36+”, White Pass 16-20”). Some locations around White Pass and potentially Paradise and Crystal developed a layer of buried surface hoar on 12/29 resulting in at least one triggered avalanche and several reports of shooting cracks and whumphfs. As the storm totals continue to grow, so does our uncertainty. If you use the break in the weather Sunday to venture into larger terrain, use extra caution. Avalanches may fail on any number of potential weak layers and even trigger larger deeper avalanches. If an avalanche occurs on the layer of buried surface hoard observed early in this storm cycle, it could be very large and destructive. Be patient and give the snowpack time to adjust to these recent loads. 

I’d like to thank all of you for submitting your observation in 2020! As of today, we have had 98 observations from the West-South zone on our public site. Your observations help us create the best possible forecast. Keep it up in 2021!

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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