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Out of date — this forecast expired 6 years ago.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

Very dangerous avalanche conditions will be found within the West South zone on Monday. Travel in avalanche terrain or near the volcanoes is not recommended. Avalanches have the capability of growing very large and running to valley bottoms.

Avalanche problems

  • Storm Slabs

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

    Above the rain/snow line, heavy snowfall and strong winds will help to overload the snowpack and trigger large to very large natural avalanches. These slides could fail on storm instabilities from this past week or at the new snow interface. Areas that are susceptible to wind-loading will have thicker and possibly more reactive slabs. We expect most avalanches to entrain significant snow, with the ability to run far distances and possibly step down to older layers in the snowpack. Even with lower hazard forecasted below treeline, slides could run down into this elevation band. Monday is not a day to be anywhere near large avalanche paths or slopes over 35 degrees.

    (2/21/2021) This natural avalanche occurred on Eagle Peak at Mt. Rainier National Park on Sunday. It started higher up on the mountain before running to the valley bottom, with a large powder cloud that crossed the river and dusted observers. [Photo: Nikki Frumkin]

  • Loose Wet

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Very Likely
    Size
    1–2

    Below the rain/snow line, heavy rain will continue to destabilize the snowpack in a number of ways on Monday. Some areas will have already seen rain and natural avalanches occur before daybreak, while other areas will see rain for the first time as freezing levels creep up. Just because a path has already slid, doesn't mean that it can't slide again. There are multiple crusts and layers of cold dry snow at all elevations for water to pool on and break the snowpack’s bonding. As the amount of liquid water added to the snowpack increases, you may first witness Wet Loose avalanches before later seeing slabs release at some of these layers of concern. The timing of wet avalanches is very difficult to predict and they can act in surprising ways. Although we can’t predict the exact timing, we can tell you that they will occur on Monday and you should stay out of avalanche terrain if you find rain falling on dry snow or that there is evidence of recent avalanches.

    (12/21/2020) This wet slide occurred earlier this season at Mt. Rainier during a large rain event. It was pushing D3 and had a 3' crown.

  • Deep Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    3

    Sunday night through Monday morning could be enough to tip the scales on the Mid-January crust we have been talking about for almost a month now. We don’t know of any recent avalanches on this layer in the zone, but the setup is still there and it has started to awaken further north in the Stevens Pass and the East Central zones. If the added load from this storm is enough to activate the Mid-January or even 2/11, very large and destructive avalanches could occur. These slabs could release naturally or be triggered by other avalanches stepping down to the Mid-January crust. Give all large avalanche paths a wide berth until this storm is over.

    (2/20/2021) This deep avalanche likely failed on the mid-Jan crust Saturday near Stevens Pass. S, 4900' Photo: Wash DOT NCR.

Avalanche Discussion

This storm is not as potent in many areas of the West South as other areas in the region. Paradise, of course, will be the outlier within the zone, where we are expecting over 3” of precipitation in the next 24 hours. That doesn’t mean that conditions aren’t very dangerous everywhere in the zone. Strong winds, heavy precipitation, a weak snowpack structure, and recent avalanches all are signs of instability. There will be several rounds of natural avalanches and we expect very large (D3) slides to occur on Monday. We could have forecasted 8 of the 9 avalanche problems for tomorrow and probably have been correct. With a complex snowpack and overlapping avalanche problems, just keep it simple by letting this storm run its course.

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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