Avalanche forecast

West Slopes North

Northwest Avalanche Center
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Avalanche danger

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

Human triggered and natural wet snow avalanches are your main concern on Tuesday, as freezing levels rise to 8000 feet. Pay attention to how wet the snow is getting, and stay off steep slopes and the runouts beneath them when you notice snow getting wetter or if you see snow sliding or rolling downhill.

Avalanche problems

  • Loose Wet

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

    Wet loose avalanches are likely with warm, springlike temperatures on Tuesday. They will probably increase in size and frequency as the day progresses. The first day that dry snow gets wet is usually when it is most reactive. Dry snow fell at upper elevations over the weekend, and it will first moisten late Monday or on Tuesday. Over a foot of low density, dry snow previously existed at the snow surface, and avalanches could run that deep or even deeper. Below treeline areas received much less snow, and that snowpack has previously been affected by water, so avalanches are not expected to be as large or reactive at lower elevations. 

    You could easily trigger wet loose avalanches on steep slopes, and avalanches could also run naturally. Travel on steep slopes and runouts beneath large avalanche paths is not recommended. If we have substantial cloud cover, all aspects will get equally wet. If we see clearing in the afternoon, avalanches may stay more limited to south and then west slopes. With this much warming and water in the snowpack, we might also encounter wet slab avalanches, which are much less predictable than wet loose avalanches. This is another reason to steer clear of steep slopes on Tuesday.

    (3/2/2022)

    Large wet snow avalanches like this one near Iceberg Lake are expected on Tuesday. 

  • Deep Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    3

    A period of warming, and larger loads such as the wet snow avalanches we’ll see on Tuesday, or a cornice fall, more likely during the warmer temperatures, could be the trigger needed for us to get a deep persistent slab avalanche. Three very large avalanches failed on a deeply buried persistent weak layer last Wednesday. We haven’t seen or heard about any avalanches on this layer since, but unsettled weather has made it challenging to see more avalanches and investigate more. These avalanches probably failed on a layer of weak facets buried on March 8, 3-4 feet deep. This isn’t really a “manageable” avalanche problem that can be figured out. You are either in the terrain where one of these large, unsurvivable avalanches could occur, or you are not. If you choose to travel in these areas you are simply accepting a slightly higher risk of triggering or being exposed to a very large avalanche. 

    (3/16/2022)

    Two very large natural slab avalanches which were seen last Wednesday. East aspect at ~6000' on Lasiocarpa Ridge.

    Photo: Lee Lazzara

Avalanche Discussion

There is a small chance that reactive slabs could still exist at the uppermost parts of the forecast zone, but we expect warm temperatures to quickly settle any of the short-lived weaknesses. Large warming events like what we’ll see Tuesday are unsettling on a previously dry snowpack. We’ve already had several this year, but this one is the first of this magnitude in over a month. Use careful decision-making if you’re heading out into the backcountry, as conditions could change quickly and snow could rapidly become much weaker and less supportable as temperatures rise. 

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