Avalanche forecast

West Slopes South

Northwest Avalanche Center
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Avalanche danger

Fri
Alpine
4 · High
Treeline
4 · High
Below
3 · Considerable
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Highlights

Expect very dangerous avalanche conditions on Thursday due to a dynamic storm that has brought heavy snowfall, gusty winds, and now rising temperatures to the West South. Avalanches will be large enough to injure, bury, or kill you. Travel in avalanche terrain is not recommended during this time period.

Avalanche problems

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Very Likely
    Size
    2

    Paradise has logged 1.5 feet of snow and counting at this time, while areas closer to the crest have been receiving significant precipitation of their own. With more precipitation on the way, Storm Slab depth will continue to increase on Thursday. Slabs will be deeper and more reactive as you ascend in elevation, or on the volcanoes where snow totals are higher. Slabs will also be larger on leeward slopes, at the base of cliffs, or on the sides of gullies where the storm snow was redistributed by the wind. Thursday will not be a day to be traveling in avalanche terrain, including where avalanches can run or stop.  But if you choose to go into the mountains, stick to low angle terrain and gather some information for another day. Watch for shooting cracks, collapses, recent avalanches, and active wind loading. Use test slopes and hand pits to look at the bond between the new and old snow, along with any interstorm layers that may be present. You can also look at the 12/21 interface to see if it is still a point of failure. 

    (12/30/2020) Crystal Mountain Pro Patrol was easily triggering Storm Slabs as deep as 2 feet in wind loaded areas on Wednesday.

Avalanche Discussion

Avalanches were releasing naturally and being triggered by humans throughout the West South zone on Wednesday. Crystal Mountain Pro Patrol reported sensitive Storm Slabs 6-8” deep releasing easily during control work, with slabs as deep as 1.5-2 feet in windblown areas. Professional Mountain Guides in the Paradise area reported mostly white-out conditions but were able to make out multiple large natural avalanches (D2) failing near common snowshoe and backcountry ski routes. With continued snow Wednesday night into Thursday morning, we expect a natural avalanche cycle to occur at some point, but the timing of them can be tricky to predict. Peak instability should be closer to the morning, but you need to keep your guard up throughout the forecast period and realize that slopes that slid on Wednesday could reload and slide again on Thursday. Other slopes that haven’t yet slid could be approaching their tipping point with the added precipitation. To add some complexity, a warm-up is expected to occur on Thursday which could lead to multiple outcomes. We could see rain at lower elevations, driving wet avalanche problems before helping the snowpack to stabilize. The height of this instability should occur when rain begins falling on cold dry snow that has fallen during the storm. At this onset of rain on snow, you should avoid traveling in and below all avalanche terrain. The warm-up may also produce heavy snow overlaying weaker snow, sitting on top of a crust. This could occur in multiple elevation bands and makes a favorable setup for natural and human triggered avalanches.

Leading up to this storm, the West South saw multiple human triggered avalanches up to size D2 occur, with some slides breaking in surprising ways. The 12/21 crust remains a point of reference in the snowpack for you to dig down to. Look at all the snow and interfaces above the 12/21 and evaluate it carefully for points of failure. Weak snow grains had been observed on the surface prior to Tuesday night’s snowfall and may now be buried, creating a weak layer. Let us know what you’re finding out there by submitting an observation.

Although the volcanoes are again set to out-produce areas closer to the crest, making them potentially more dangerous, we still expect natural and human triggered avalanches throughout the zone. We’ll have to see how the weather plays out on Thursday, but it will certainly be a heads up day.

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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