Lawinenlagebericht

West Slopes South

Northwest Avalanche Center
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Lawinengefahr

Tue
Hochgebirge
3 · Erheblich
Waldgrenze
3 · Erheblich
Unterhalb
3 · Erheblich
Open full map
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Kernpunkte

A significant winter storm will bring a big change to the mountains and the avalanche danger. Even though the lure of the new snow is strong, Monday will be a good day to take a more conservative approach. You may trigger avalanches on any steep open slope.

Lawinenprobleme

  • Wind Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Likely
    Größe
    2–2.5

    Near the Cascade Crest and higher on the volcanoes, the wind will likely be the greatest driver of avalanche hazard. Strong winds should easily transport snow and form firm deep slabs. These harder slabs may break widely and fail above you. Give them a wide berth. Add to this problem the possibility that some of these slabs may sit on weak older snow and you have the makings of a dangerous setup. Fortunately, they should be easy to identify and avoid. Look for scoured slopes and drifts to help anticipate which aspects and features hold wind slabs. Avoid steep slopes with smooth pillow-like slabs or firm and hollow-sounding snow. Any of these winds slabs could easily be large enough to bury and kill you.

    (12/28/2021)

    Example: Sharp cornices like these can indicate winds slabs below. 

    Photo: Andy Harrington

  • Storm Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Likely
    Größe
    1–2

    At lower elevations and in wind-sheltered areas you may trigger slabs at the base of the storm snow or on layers with the new snow. Some of these slides may fail easily, break widely, or wrap around features. Even though we’re used to storm slabs in the West South zone, some of these avalanches could fail on weak older snow making them surprising. Unfortunately, the variable nature of the old snow surface (see discussion for more details) could make predicting how any particular slope will react very difficult. You can use small slopes and hand pits to investigate how the new and old snow are bonding. However, remember with this variable interface, just because ‘this slope’ didn’t fail doesn’t mean ‘that one’ won’t. 

    Near the volcanoes, significant snowfall is expected. This could build some pretty large storm slabs near and below treeline. If you travel in these areas, use extra caution.

    (1/28/2022)

    Large surface hoard and small near surface facets were seen on a variety of slopes in the Crystal backcountry. These grains were typically seen on NW-NE aspect, but could be found in any shaded area.

    Photo: Dallas Glass

Avalanche Discussion

In some ways, this is a simple forecast. A big change in the weather like this often leads to big problems (avalanches). However, the timing of this event makes it tricky. How much snow falls after snowlevels drop could make a huge impact on the danger. Fortunately, the peak of the hazard should be Sunday night during the most intense precipitation. However, you could see natural avalanches Monday during periods of heavy snow or strong winds. Pay attention to the weather forecast for the location where you want to travel. If what you see in the mountains doesn’t line up with the forecast, the avalanche danger may be incorrect as well. 

Prior to this storm, numerous observations from all across the West South zone described the surface as “firm” and “variable.” Very icy surfaces were often encountered on the volcanoes and on more southerly facing slopes close to the crest. Near-surface facets and facet-crust sandwiches were observed on more shaded slopes particularly near Crystal Mt and White Pass. While some reports of surface hoar were received, it appears spotty and not nearly as widespread as the sugary facets. Below this new interface, the snowpack is strong and well settled. We don’t have any layers of concern deeper in the snowpack. This should make observing these potential weaklayers easy. Any avalanche concern should remain near or above the previous snow surface.

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