Avalanche forecast

West Slopes Central

Northwest Avalanche Center
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Avalanche danger

Thu
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
2 · Moderate
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Out of date — this forecast expired 4 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

A storm dropped well over a foot of low density powder in the mountains through Tuesday. It’ll take a while for the snowpack to adjust to the new load, so travel conservatively on Wednesday as it’s likely that you could trigger an avalanche. Avoid steep slopes during your travels, and if you see any obvious signs of instability such as long, shooting cracks and recent avalanches, give steep slopes an even wider berth.

Avalanche problems

  • Storm Slabs

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

    Natural avalanches of nearly every variety, from dry loose to storm to wind slab, were reported in all the neighboring zones on Tuesday.  You can still expect to see a variety of storm snow avalanche problems on Wednesday. Natural avalanches will probably be less likely to occur than yesterday, and you may find it a little harder to trigger an avalanche. We're not quite sure exactly how quickly these problems will go away, so play it conservative on your outing.

    Your highest chances of encountering a storm slab are in areas where a warm period midday Tuesday lent to an upside down snow structure especially in the mid and lower elevation bands.  These upside down surface layers, where heavier snow sits on top of lighter, fluffier snow could still avalanche with a human trigger. This layer is shallow enough, around a foot deep, that you can dig down with your hands to find if thicker, heavier snow sits over a softer layer and breaks off easily in your hand pit. As you travel up in elevation more wind will have affected the low density snow and drifted it into firmer and/or thicker deposits. These could range from slabs that are hard enough that you sink in minimally, to a very subtle increase in snow hardness from the nearby non wind-affected snow.

    If you encounter any slablike qualities of firmer snow over softer snow, whether wind affected or not, it is best to avoid slopes over 35 degrees. You're most likely to trigger a slab avalanche on steep, convex rollovers or in gullies like the photo accompanying this problem shows. They also frequently trigger around rocky outcroppings, or just below ridgelines, especially if the snow is wind-affected.

    (2/13/2021)

    This slab avalanche failed in the new snow layer, spanning the width of this steep rollover, a likely location for an avalanche to fail. Photo: Tom

    Photo: Public Ob

Avalanche Discussion

If you find loose, low density snow on steep slopes you could trigger a dry loose avalanche. Pay attention to the possibility of triggering one of these more predictable types of avalanches if you enter a steep slope. Partly cloudy skies might mean that even on the winter solstice south facing slopes might have a few loose snow avalanches running on them as the sun shines onto the steeper surfaces. Despite saying this, it's forecasted to stay very cold Wednesday, so be sure to prepare for the low temperatures. 

Buried surface hoar may exist in areas where the wind did not destroy it, which is generally at lower elevations. This was buried on 12/18, and is now 2 or more feet deep. We're unclear how reactive this layer may be. If it is preserved anywhere, triggering an avalanche on it would be two or more feet deep, and could propagate further than expected.

Regions covered