Avalanche forecast

West Slopes South

Northwest Avalanche Center
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Avalanche danger

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

The West South zone is slowly emerging from a long stormy week. Lots of new snow and several surprising avalanches suggest a bit of caution is in order. Give the snowpack time to heal by staying off of steep slopes at middle and upper elevations.

Avalanche problems

  • Storm Slabs

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

    We’re measuring the snow totals from this storm in feet all across the zone. A cooling trend helped much of the snow fall right-side-up and didn’t leave too many concerning weakness. Even still, all this new snow needs time to settle and heal. You’re most likely to trigger a slab avalanche at upper elevation, in wind-affected terrain, and on steep convex slopes. Unfortunately, simple uptrack and small slope tests probably won’t help you assess this much storm snow. The only real way to look will be to stop and dig, and even that might not give you the full story. This is when patience is key. Staying away from steep open slopes might be the only solution. 

    With the uptick in winds, expect significant drifting along ridges and other exposed slopes. Wind-loaded pockets could form quickly during the day. Southerly winds might create a very unusual loading pattern in the terrain. 

    (1/19/2024)

    Example: You could still trigger avalanches in the storm snow on convex rollovers and very steep terrain. 

    Photo: White Pass Ski Patrol

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely
    Size
    2.5–3

    We’ve been tracking weak layers in the snowpack all month. For the longest time, we didn’t seem to have the slab or a load. Well, if this storm didn’t do it, we’re not sure what will. Crystal Mt Ski Patrol triggered numerous persistent slabs Thursday with explosives and skis in terrain that has been closed and uncontrolled for the entire month. Sure these are inbounds observations, but they are compelling evidence for our backcountry snowpack. 

    The distribution of these weak layers is hard to pin down. They often formed equally across the landscape, but multiple wind events, sunny days, and other storms made the distribution irregular. It may be nearly impossible to say if any one avalanche path can produce a deep slide. The pattern may be indecipherable even within a local area. 

    Given this setup, you may not see any obvious clues that let you know to tuck tail and run until its too late. Consider fully avoiding larger avalanche paths and limiting or eliminating time in their tracks and runouts.

    (2/29/2024)

    A widely propagating avalanche at Crystal Mt failed on older snow layers (2/14). 

    Photo: Dallas Glass

Avalanche Discussion

In some ways, Friday is a normal post-storm powder day, but in many, it’s not. Very stormy weather limited information this week, and we still don’t have a great handle on all the new snow and its potential layers. The volcanoes also received impressive storm totals likely exceeding 3-5ft since 2/27. Our partners at the USGS reported several more avalanches on Thursday. On Mt St Helens, two very large D4 avalanches occurred on the E side of the mountain. These correspond to similar size slides further south on Mt Hood. While not nearly as huge, five large D2+ slides were recorded on the south side of Mt Rainier. We don't know if any of these were persistent slabs, but some photos of very widely propagating avalanches on Mt St Helens and Mt Adams suggest it's possible. Closer to the crest, observations from Crystal Mt (avalanches) and White Pass (snow profile) continues to show weaklayers linger in the upper snowpack. 

Below all the storm snow, several older weak layers continue to linger. The most concerning seem to be the 2/14 surface hoar/facet layer and the facets over the prominent Early February Crust. At the end of the day the difference between the 2/19, 2/14, 2/11, and EFC is probably inches. These layers are often 3-6ft (1-1.5m) below the surface. 

The other thing to watch on Friday is the sky. You’ll see moments of sunshine. If you start to feel temperatures warming expect tree bombs and maybe rollerballs on steep slopes. If these start to entrain snow, you could see loose slides.

Given all the new snow, snow immersion and tree wells are a big concern. Keep your partners in sight and have a plan to communicate with each other. 

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