Avalanche forecast

West Slopes South

Northwest Avalanche Center
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Avalanche danger

Tue
Alpine
4 · High
Treeline
4 · High
Below
3 · Considerable
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Out of date — this forecast expired 6 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

Recent avalanches, persistent grains in the snowpack, heavy snowfall, increasing winds, and warming temperatures all point to very dangerous avalanche conditions on Monday. Let the storm run its course by keeping away from all avalanche terrain.

Avalanche problems

  • Storm Slabs

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

    We expect both human triggered and natural avalanches to be widespread on Monday, with larger slabs as you ascend in elevation due to the wind’s influence. So far this weekend, Storm Slabs have been easily triggered by humans and propagated the width of the feature, and naturals have been observed. Most of these slabs have failed on weak snow at the 2/11 interface. If this interface continues to be active on Monday, avalanches could continue to propagate far distances and wrap around terrain features or be remotely triggered.  Any triggered avalanche could entrain much of the recent storm snow and gauge down toward deeper layers in the snowpack, growing large enough to kill you. You should avoid all terrain where avalanches can run or stop on Monday.

    (2/14/2021) This was one of multiple natural slab avalanches observed near White Pass on Sunday (2/14) by NWAC forecasters. Crown depths were estimated to range from 10 inches to 2 feet in places.

  • Deep Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2–3

    Another major loading event will further test our buried persistent deep layers. You may have been traveling around the zone recently and not seen any signs of instability on these deeper layers, but that doesn’t mean that they shouldn’t be a factor in your decision-making process. A lack of direct feedback could lead you to believe that these layers have started to move toward the low-likelihood, high consequence category. We’re not there quite yet, but even if that’s true, adding a significant load plus a widespread avalanche cycle above them seems like a logical time for them to awaken. Monday is not a day to tempt fate. Any avalanche occurring on these layers would most likely be fatal for anyone caught in their path.

    (2/6/2021) This slab was intentionally triggered by a small cornice drop on Saturday (2/6) in the Crystal backcountry. It propagated widely and is believed to have run on the Mid-January crust/facet combo. [E aspect, 6300'. Photo: Jeremy Allyn]

Avalanche Discussion

We have seen a lot of recent avalanches across the West South, which means that the upper snowpack is unstable. Large (D2) naturals, plus human triggered soft slabs that propagated widely or were triggered remotely have been reported at both White Pass and near Crystal Mountain. Paradise has been closed for most of the weekend, but a report from the rangers let us know of a natural avalanche that hit the road on Friday. We are now expecting a large amount of new snow which we believe will come in much heavier than the snow we currently have near the surface. Heavy snow over weak snow is a good recipe for avalanches. Recent avalanches plus a good setup for new avalanches is the meat of the forecast and should be enough for you to know that you don’t want to be near avalanche terrain on Monday. 

If you want to nuance it a bit more, we also have a known weak layer (2/11) that has been consistently producing surprising avalanches for both professionals and recreationalists this weekend. Many of the avalanches alluded to above failed on this layer at White Pass and near Crystal. Avalanches on Monday will be larger and could also break in surprising ways on this layer, naturally or by human trigger. The 2/11 interface was found to be 45-55 cm deep on Sunday by NWAC forecasters and contained weak snow grains, which is why these slides are breaking easily and propagating far distances. Throw in a few other sensitive density changes in the upper snowpack, and you have plenty of failure points for avalanches.

The last piece to this puzzle are those buried persistent weak layers. The Mid-January crust was measured to be about 5 feet deep on Sunday at White Pass. Depth may vary across the zone, but in all areas these layers are deep. As stated above, with so much other activity going on, those layers will be tested and we will have to wait and see what happens. We don’t have enough confidence to say that they will not be activated but we are confident in saying that we wouldn’t want to be anywhere near a large avalanche path on Monday due to the possibility of these layers failing.

You also need to recognize that so much recent snow can be a hazard on its own. Learn more about snow immersion hazard here.

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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