Avalanche forecast

West Slopes South

Northwest Avalanche Center
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Avalanche danger

Tue
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
2 · Moderate
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Highlights

Rain will soak our snowpack up to ridgecrest throughout the West South zone on Sunday night. Wet slides are likely to occur, possibly even after precipitation has switched to snow. Given the high uncertainty associated with wet snow, you may want to consider avoiding avalanche terrain until this storm has wrapped up.

Avalanche problems

  • Wet Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    2–2.5

    By the time Monday rolls around, there is expected to be plenty of water in the upper snowpack, and we will have likely experienced a natural wet avalanche cycle overnight. How much activity will linger into the daylight hours becomes the question mark. Wet avalanches are impossible to predict with precision and can often occur long after the rain has stopped. As we've already seen this spring, this can even occur days after a rain event. So it's likely that wet avalanche activity will continue into the daylight hours on Monday, even as temperatures lower and upper elevations switch to snow. This includes wet slabs, glides, cornice falls, or falling blocks of snow from rocky ledges. You can't predict where or when these slides will happen, so your best mitigation tool will be avoidance. Avoid lingering beneath overhead hazards, such as sagging cornices or precariously hanging blocks of snow. Steer clear of large avalanche paths or slopes containing glide cracks. 

    (3/26/2025)

    A very large wet slab from our last atmospheric river. Similar slides could occur during this storm. Some may even fail to ground like this one in isolated locations.

    Photo: Andy Harrington

  • Storm Slabs

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

    We expect a general cooling trend on Monday, which will likely bring snow back to mid- and upper-elevation areas. Snow will be accompanied by moderate to strong winds, creating larger drifts on leeward features. Look for slabs to develop on slopes over 35 degrees, particularly if they're wind-loaded, convex, or unsupported. Although a decent bond is expected with the warm and wet surface, this snow is considered weak. It could behave much differently than you're used to. We're mixing avalanche problems in a way, but if you can make it to upper elevations, you'll want to avoid slopes steeper than 35 degrees until this storm wraps up and we build a stout crust.

    (2/25/2025)

    At upper elevations, you may encounter shallow storm slabs such as this one from earlier in the season.

    Photo: Andy Harrington

Avalanche Discussion

This is my final forecast of the season, and I would say that I have the highest level of uncertainty I've experienced all year. To say that this storm, our current snowpack structure, and the intricacies of what may happen on Monday are dynamic would be an understatement. So here's what we know.

We haven't had a solid overnight freeze in our zone since last Wednesday night. Thus, the snow surface going into this rain event is warm and weak after several warm days. This weak snow sits over a melt-freeze crust formed by our last atmospheric river (AR) event. This crust is variable in thickness but is not considered stout in most locations. Below the AR crust, older melt forms exist, which are also weak. During the recent warm weather, natural and human-triggered wet avalanches have occurred. On Sunday, a potentially very large glide avalanche was spotted in Mount Rainier National Park by Crystal Mountain Patrol. Perhaps an indication of things to come?

The uncertainty surrounds how much rain will enter the snowpack, at what elevations, and what that means for wet avalanches. Fluctuating freezing levels, strong winds, and several rounds of precipitation make it challenging to pinpoint. Rain is currently falling at upper elevations and will continue to do so before freezing levels slowly lower. So, even areas that seem snowy in the morning will already have free water in the snowpack.

We feel confident that wet avalanches will occur during this event. Cornices will fail, snow will fall from rocky ledges, and loose slides will occur. The burning question is if we are getting enough water to break down the March AR crust and get into those deeper, weaker melt forms. If we do, the size of potential avalanches could grow exponentially, similar to what we saw during last week's atmospheric river event. Perhaps a larger trigger, such as a cornice fall, could do the trick. With so much weak and wet snow, if enough mass gets moving, slides can gouge down into old layers and entrain significant snow. Although the hazard rating is considerable, you may want to consider avoiding all avalanche terrain until the storm has concluded. 

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