Lawinenlagebericht

West Slopes South

Northwest Avalanche Center
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Lawinengefahr

Sun
Hochgebirge
3 · Erheblich
Waldgrenze
3 · Erheblich
Unterhalb
2 · Mässig
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Kernpunkte

A weak layer of snow has been sending messages of instability and causing avalanches in the Crystal backcountry. We do not know if this layer exists in other parts of the zone. As we receive more snow and wind on Saturday, look for signs of instability such as shooting cracks and whumpfing collapses as a sign to dial back your terrain choices.

Lawinenprobleme

  • Wind Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Likely
    Größe
    1–2

    On Saturday, you may not be dealing with your standard Wind Slab in the West South zone, and therefore you need to take a more cautious approach. In areas such as Crystal, we know that buried weak snow grains are sitting atop the 1/13 crust and starting to cause avalanches as slabs begin to develop. Shooting cracks, whumpfing collapses, and easily triggered pockets of wind-deposited snow have been observed, most prominently on slopes with a southerly aspect. We have no idea if these weak snow grains exist in other areas of the zone such as Paradise, Mt. Saint Helens, or White Pass. The only way for you to tell is to dig down to the 1/13 crust and look at the snow just above it to confirm their existence. Areas such as Mt. Saint Helens and Paradise are predicted to get larger snow totals on Saturday and if those weak snow grains exist on the volcanoes, very dangerous avalanche conditions could develop. 

    We believe that wind loaded areas are where the most slab potential currently exists throughout the zone to possibly fail on those persistent grain types. We often talk about how areas that receive more snow can build larger and potentially more dangerous slabs. That may not be the case on Saturday, when areas that contain those persistent grain types may pose a greater hazard regardless of the amount of new snow. Throughout the zone, precipitation and moderate winds will create hazardous fresh slabs, regardless of the existence of weak snow grains. New slabs will be most likely on leeward slopes near ridgelines, on the sides of gullies, or the base of cliffs. As you travel, look for textured snow surfaces and use test slopes to check the reactivity of all the snow sitting atop the 1/13 crust. Avoid slopes greater than 35 degrees if you suspect that they are wind-loaded or find a cohesive slab over weak snow grains in your pits.

    (1/28/2021) This avalanche was remotely triggered by a skier in the Crystal backcountry on Thursday. You can see the shooting cracks initiating where the skier is standing.

Avalanche Discussion

Observations from many areas of the West South are limited, leaving us with a great deal of uncertainty heading into this weekend. What we do know is that a firm crust (1/13 AR) exists throughout the zone and that in some areas, weak snow grains sit atop this crust. We have positively identified these grains on all aspects and elevations in the Crystal backcountry and observations lead us to believe they may exist elsewhere in the zone. Snow depth above the 1/13 varies throughout the zone, but all areas should be dealing with a foot or more of snow by Saturday. To date, the snow has been fairly low density and therefore hasn’t been able to really drive a slab avalanche problem. That started to change on Thursday at Crystal when areas that contained a slab began triggering more easily, propagating widely, and running downhill quickly. An observation from Mt. Saint Helens on Friday let us know about a small slab avalanche that was remotely triggered on a test slope. We expect that with a slight bump in temperatures and added precipitation this weekend, we could see more slab development, resulting in more avalanches. As conditions change, those red flag signs of instability such as shooting cracks and whumpfing collapses should give you pause and steer you to low consequence terrain. As we navigate this complex setup with a bit of uncertainty, we’d appreciate hearing what you are seeing out there if you can take a few minutes to submit a public observation. 

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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