Avalanche forecast

West Slopes South

Northwest Avalanche Center
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Avalanche danger

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

If you are not standing on a firm crust on Wednesday, then you are in snow capable of producing dangerous avalanches. The type of avalanche you need to be aware of will switch from wet to dry as you ascend in elevation with either type of avalanche capable of being large enough to bury or kill you. Avoid slopes greater than 35 degrees if you ascend above the rain/snow line.

Avalanche problems

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    2

    The West South has had almost continuous precipitation since Monday morning in the form of both rain and snow. This has essentially created two elevation bands, delineated by the rain/snow line. As you ascend in elevation above this line, expect to find colder, drier snow and dangerous Storm Slabs. These slabs should be large, particularly if strong winds on Tuesday night are able to redistribute the snow into thicker slabs on leeward slopes. We are most concerned with new slabs formed the past few days having a poor bond to the old snow surface (1/11 interface) as well as interstorm layers within the slab. Take some time to investigate these bonds and how much snow makes up any potential slab. You can use test slopes or hand pits as you travel to give you an indication of slab potential and its reactivity. If you find a poor bond, see other avalanches, or heavy snow over weak snow, avoid all avalanche terrain where avalanches can start, run, or stop.

    (1/12/2021) This Storm Slab (D2) naturally triggered during the onset of rain on 1/12 at Crystal Mountain. We expect there to be hundreds of these types of slides across the zone.

  • Loose Wet

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2

    Below the rain/snow line, you should find much different conditions. The rain produced a widespread natural avalanche cycle on Tuesday and we expect that to continue on Tuesday night. As temperatures cool and the bulk of the precipitation exits our zone, natural avalanches should taper on Wednesday. That’s not to say we’ll be home-free. Even with decreased likelihood, the snowpack still needs time to adjust to all the recent rain and may still be capable of producing surprising wet avalanches, especially earlier in the day. 

    Although listed as Wet Loose, other wet snow related avalanches such as Wet Slab and Glide are still on our minds and these problems are often intermingled. Wet Loose avalanches often start at a point and are capable of entraining lots of snow, triggering slabs, and traveling far distances as they descend. Rollerballs, pinwheels, and fan-shaped avalanche debris are signs of wet loose avalanches. If you notice these signs, steer around terrain features greater than 35 degrees and avoid terrain traps such as creeks, gullies, or cliffs. Anywhere you find unconsolidated wet snow, be leery of traveling on steeper slopes and avoid traveling underneath steep rocky slopes and cliff bands where snow could shed from above.

    (1/1/2021) Large natural loose wet avalanches on the road to Paradise. This occurred during a previous avalanche cycle where rain fell on fresh snow earlier this month. Mt Rainier National Park . W aspect 4100'. Photo: NPS Rangers

Avalanche Discussion

As of Tuesday afternoon, Crystal is the current West South leader for water numbers, with a whopping 4.02”. It’s not often that Crystal outpaces Paradise, who has a respectable, 3.58” of water in their own right. White Pass often runs similarly to Crystal, but in this case is reporting 2.13” at NWAC’s weather station. All of these numbers are impressive, and more precipitation is on the way Tuesday night. Observations were extremely limited as one might expect, but Crystal Mountain Pro Patrol reported natural slab avalanches in the ski resort this morning as snow switched over to rain. As we extrapolate that data into other parts of the zone, we can be confident that widespread naturals did occur on Tuesday and feel confident that there will be more naturals on Tuesday night as more precipitation and rising freezing levels impact the zone. If this additional water and warmup were to be occurring during our forecast period, we would continue to be at High avalanche danger. However, by daybreak on Wednesday, the bulk of precipitation should be done with, and freezing levels should be lowering, finishing this wet couple of days with cooling temperatures to help us on our journey to better stability than we have seen recently.

This doesn’t mean that you should let your guard down on Wednesday. We just received a lot of water in a short period of time, and the snowpack does not like rapid change. The avalanches reported by the Crystal Patrol on Tuesday were large (D2), with larger naturals (D3) reported in the neighboring Snoqualmie Pass zone. Although the natural cycle may be coming to a close, human triggered avalanches of the same size are expected on Wednesday. The snowpack still needs time to adjust to the large volume of water it recently received. As temperatures cool and the snowpack starts to freeze from the surface down, remember that it can take some time for water to percolate through the snowpack. Surprising wet avalanches can still occur hours after the rain has stopped. Elevations above the rain/snow line should hold significant snow totals and could produce very dangerous avalanche conditions, ease into terrain and stay off slopes 35 degrees and steeper. At lower elevations, rain effects may be significant, with open creeks, collapsed snow bridges, and heavy wet snow.

During the ongoing Covid-19 pandemic, continue to follow the latest guidance from local, state, and federal health officials. Avoid unnecessary risks that could impact first responders and stress medical resources.  Wear a mask when appropriate, practice social distancing, and consider recreating closer to home.

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