Avalanche forecast

West Slopes South

Northwest Avalanche Center
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Avalanche danger

Thu
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
2 · Moderate
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Out of date — this forecast expired 4 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

Buried weak snow continues to be a problem in the West South zone and should be shaping your travel plans. Seek out lower-angled or heavily treed terrain to help minimize the potential for triggering a slide that would likely be large enough to bury or kill you. You will likely only get feedback from this low-likelihood, high-consequence avalanche problem if you take the time to dig in the snow for yourself.

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1.5–2.5

    Persistent Slab problems are tricky. Tricky to manage, tricky to forecast, and tricky to put to bed. They can fail in surprising ways by spanning far distances, breaking above you, or wrapping around and connecting terrain features. You should be traveling cautiously in terrain and doing your homework before committing yourself to a slope. Think about traveling as if conditions are Considerable, not Moderate, even though the likelihood of triggering one of these slides isn’t very high. In fact, you could be out all day and not see a single sign of instability. You may have to dig in order to find out what potential issues lurk beneath the surface.  

Avalanche Discussion

NWAC forecasters were again out in the field on Tuesday tracking the 12/8 interface that has us a bit on edge in the West South. This layer continues to be highlighted by quick snowpack tests and produce medium failures when more formalized tests are performed. On Wednesday, we’ll be 4 days out since our last major loading event, and the fact that this layer is still showing up in snowpack tests should give you all the information you need to know. It is not healing as quickly as we are used to seeing with a standard Pacific Northwest storm interface.

You can likely find this layer 1-1.5 feet below the surface on all aspects and at most elevations. Take a moment and check it out for yourself before you commit to a slope, it could change your mind about what you’re about to do. Although Tuesday is the first day since the start of the storm when we have not received a report of a new avalanche, that doesn’t mean all is roses and lollipops. Don’t ignore these recent red flag signs of instability. Combined with the known buried weak snow, you should have enough information right in front of you to realize that you should be traveling cautiously in the mountains, seeking out lower-angled or heavily treed terrain. 

Although we do not have any direct observations from Mt. Adams or Mount St. Helens, we do have data from just to the north and just to the south of our southern volcanoes. It’s not a stretch to assume that the problem resides in these areas as well and you should take the same precautions outlined above. You can also check out the Mt. Hood forecast for more information on the recent avalanches that have occurred on the 12/8 layer in that zone. 

Apart from the lingering persistent issues, winds were slightly gustier than forecasted on Tuesday. While some snow transport was observed, it likely wasn’t enough to form new Wind Slabs. Still, keep an eye out for areas that look “fat” or have rippled surfaces near rocky gullies or cliffs, especially if you see snow actively being transported on Wednesday. These are features where triggering a lingering wind-loaded pocket may be more likely. You could also see some snow shedding from trees and rocks in the sunny weather. While unlikely, these sheds could entrain some snow on steeper slopes and fan out into a small debris pile. We don’t anticipate any of these growing large enough to become an avalanche of consequence. 

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