Avalanche forecast

West Slopes North

Northwest Avalanche Center
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Avalanche danger

Sat
Alpine
4 · High
Treeline
4 · High
Below
3 · Considerable
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Highlights

Large and very large, dangerous avalanches are expected to continue to occur naturally as the warm wet weather remains through Friday. Every type of wet snow avalanche could be happening, and they are expected to be very destructive, although upper reaches of our forecast zones are still seeing dry snow avalanche problems. Avoid avalanche terrain, which includes steep slopes and the lower angle areas beneath the steep slopes on Friday. 

Avalanche problems

  • Wet Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Very Likely
    Size
    2–3

    It's not over yet! 6500ft freezing levels and precipitation will continue through Friday, and very large avalanches will run. From our limited observations on Thursday we gathered that many large (D2) avalanches ran naturally in wet, heavy surface snow. The avalanches picked up a lot of mass as they traveled downhill, ending in several-foot-thick debris piles. Water will percolate further down into the snowpack, potentially causing larger and deeper avalanches on Friday. Since the initial wetting and natural avalanche cycle occurred Thursday, we don't think avalanches will occur quite as frequently on Friday as they did the previous day, despite possibly being larger.

    Glide avalanches will probably be waking up on steep, smooth faces, in addition to concerns of large sagging cornices breaking.  In below treeline areas, most snow surfaces were old melt forms that could withstand the rain, although towards the upper reaches of the BTL some low density snow was present. This would have been impacted by the rain and warming with natural avalanches Thursday. A human-triggered avalanche could still probably occur at lower elevations. Keep in mind that concerns remain regarding large and very large avalanches running from higher elevations down to lower elevations. Avoid traveling in avalanche terrain on Friday. 

     A large debris pile from a natural avalanche on Mt Herman which occurred during a storm on 1/12/21, exactly 2 years ago. These huge debris piles are probably very similar to ones that we'll see after this storm passes through: very large, and not something you'd want to get caught up in.  Photo: Trevor Konstanich

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Very Likely
    Size
    2–3

    The top of our above treeline elevation band is probably hanging onto dry snow for the duration of this storm. As of Thursday evening, the 3 inches that's fallen as rain down low probably equates to about 3 feet of snow up high, plus another 2-3 feet by the end of the day Friday. Slopes that haven't slid yet are ripe as more and more snow weights the slope. These avalanches could be as deep as the new snow layer, or possibly even deeper, breaking where we saw several natural avalanches on Tuesday. Winds are remaining moderate to strong so even thicker slabs, probably more reactive, compound the problem. Temperatures will finally begin a slow cooling in the afternoon, giving us slightly lighter and fluffier snow, however the majority of this storm's snow has come in upside-down. This means lighter snow from earlier in the storm is beneath the more recent heavier snow on top, indicating an unstable snowpack. This is a recipe for avalanches that will remain very likely to avalanche with a human trigger until the snowpack has had a bit more time to adjust. 

    An older image of a large, destructive slab avalanche, which we expect to be continuing to happen at higher elevations as the storm continues. 

    Photo: Pete Durr

Avalanche Discussion

Observations are very limited and we have a lot of uncertainty about how the snowpack will react to all this water and added weight, so this is a day to travel very conservatively in the backcountry. It's been a busy week with natural and human-triggered wind slab avalanches reported from the weekend through Tuesday until this recent atmospheric river arrived. We quickly transitioned to mainly wet snow avalanche problems. Freezing levels rose at the start of the storm, and rain quickly caused a natural avalanche cycle Thursday, which we suspect will sustain through Friday as the precipitation continues to fall. A slow cooling begins Saturday, as the snowpack will finally begin to drain. 

Regions covered