Avalanche forecast

West Slopes South

Northwest Avalanche Center
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Avalanche danger

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

A potent storm will continue to deliver heavy snow and strong winds to the West South zone on Monday night and Tuesday, creating dangerous avalanche conditions. If you notice red flag signs of instability such as shooting cracks or recent avalanches, avoid slopes over 35 degrees or wind-loaded terrain where you’re more likely to trigger an avalanche.

Avalanche problems

  • Storm Slabs

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

    On Tuesday, continued snow and increasing winds will help to thicken existing Storm Slabs around the West South zone. These slabs should be larger as you ascend in elevation above the rain/snow line and in wind-loaded terrain. Higher snow totals are expected on the volcanoes, which may lead to larger and potentially more sensitive slabs. You can use quick hand pits, small test slopes, or uptrack tests to gather information about slab potential and points of weakness in the upper snowpack. With several rounds of precipitation and fluctuating freezing levels during this storm, there could be multiple interstorm layers to check for heavy snow over weak snow. You're also going to want to check the bonding to the previous surface.  You may be able to trigger an avalanche on any slope over 35 degrees or in wind-loaded terrain.

    Weak snow above the Early March Crust has been identified in multiple locations around the zone and could come into play during this cycle. If it does, slabs could break in surprising ways and span far distances. Take a look at the discussion below for more details.

    (3/13/2022) Shovel tilt test highlighting the 3/8 facets over the Early March Crust. All of the snow above this crust should be suspect during this storm. Photo: Dallas Glass

  • Loose Wet

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1

    Lower elevations have seen several rounds of rain recently and should be well suited to handle more. That said, the dynamic nature of this storm and fluctuating freezing levels means that we can’t rule out the possibility of a lingering wet avalanche. You should be able to tell where the rain/snow line is by looking for wet and sticky snow or existing snow in the trees. Below this line, keep an eye out for new fan-shaped avalanche debris or fresh rollerballs during your travels to help indicate another round of wet avalanches are possible. Any potential wet avalanche should occur on steep slopes and be relatively small. That said, they can be powerful and you don’t want to get caught off guard by one near terrain traps such as cliffs or open creeks.

    (3/11/2022) Wet sticky snow like this lets you know the surface may be unstable and Wet Loose avalanches are possible. Photo: Dallas Glass

Avalanche Discussion

As is often the case in our large and varied zone, Monday brought a range of precipitation totals and weather inputs. NWAC weather stations at Paradise recorded close to an inch of water, resulting in about 8” of snow. Closer to the crest, weather stations recorded significantly less, resulting in anywhere from 2-4” of new snow. The largest wave of precipitation is set to hit the West South on Monday night into Tuesday and totals will again vary across the zone. Although considered a weak atmospheric river by many, this is a strong storm more in line with what we often see in the Cascades. We anticipate that a natural avalanche cycle will occur overnight during the height of precipitation intensities. On Tuesday, temperatures should slowly cool and snow showers should become more showery throughout the day. The question mark will be the timing of the transition between these periods. If you find that heavy snow is still falling in the morning, there may be an increased likelihood for natural avalanches and potentially very dangerous avalanche conditions, particularly on the volcanoes. Strong winds and continued precipitation throughout the day on Tuesday could revitalize natural activity or reload slopes that have already slid. Choose terrain carefully and give the snowpack time to adjust for the duration of this storm. 

The Late March Crust is a prominent snowpack marker throughout the zone and should be the baseline for any snowpack tests you perform on Tuesday. All of the snow above it is in play for avalanches during this storm, and avalanches have the potential to run far distances on this firm bed surface. Additionally, we have been tracking some weak snow (facets) just above the Late March Crust throughout much of the zone. We have mostly found them on northerly slopes at mid to upper elevations, but they have been identified on other aspects on the volcanoes. If you are in an area that is harboring these persistent grain types, avalanches could act in surprising ways by connecting terrain features, spanning far distances, or breaking above you. They could even be triggered from far distances in isolated locations.

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