Bollettino valanghe

West Slopes South

Northwest Avalanche Center
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Pericolo valanghe

Sun
Alta quota
3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
2 · Moderato
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In sintesi

Don’t let the lure of fresh snow cause you to overlook the big weather events of the week. Give the snowpack time to adjust to the recent snow, wind loading, and potential sunshine. Stay off of open slopes greater than 35 degrees especially at mid and upper elevations. 

Problemi valanghivi

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    1–2

    The strong westerly winds seemed to define the recent storms for the West South zone. They easily transported snow, sculpted then snow surface, and likely formed slabs even well below ridgeline and in the trees. Pay attention to how the snow looks and feels to help you anticipate which slopes and features could hold wind slabs. When you see a textured snow surface or find firm or hollow snow, expect wind slabs on similar aspects. Steer around wind-loaded terrain and seek out less wind-affected or lower-angled areas.

    (2/20/2021) Example: This human triggered wind slab avalanche occurred Saturday 2/20 in the Crystal backcountry. S, 6000' Pickhandle Pt. Photo: Jen Daniels.

  • Loose Wet

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–2

    The snow may experience a big change on Saturday if the sun comes out. You could see natural loose avalanches on any very steep slope receiving direct sunshine. While we expect these slides to remain isolated to very steep slopes, they could entrain snow and grow larger. If you start to notice the snow shedding from rocks and trees or see new rollerballs, the snow surface is becoming wet and unstable. Steer around similar slopes and even give the runouts of these paths a wide berth.

    (2/24/2020) Example: Rollerballs like these are a great indication that the snow surface is becoming wet and unstable. They can be the precursor to loose wet avalanches. When you see new rollerballs, steer away from similar slopes.

  • Deep Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Unlikely
    Dimensione
    3

    The atmospheric river event significantly tested the deeper layers in the snowpack this past week. However, recent very large slides on Hwy 20 and Hwy 2 should have us all questioning our assumptions regarding this layer and its potential to produce avalanches. The high level of uncertainty and disastrous consequences surrounding this problem should factor into the terrain you choose. Consider limiting your exposure to any large avalanche path even those that start far above where you intend to travel. Many recent slides have run to the bottom of their runouts and even broked mature trees.

    (2/25/2021) Several avalanches once again hit Highway 20 in the Newhalem (closed from milepost 120) area on Thursday. Photo: WA DOT, NCR

Avalanche Discussion

Most locations around the West South receive 1-2’ of snow since Feb 25th. This adds to the jaw-dropping totals for the month of February. This recent storm combined with very strong winds shaped the snow surface in many areas. Very active weather periods like this need time for the snowpack to adjust. Don’t let the lull in the weather short-cut your decision-making process. 

While we continue to focus on the new snow, several layers exist in the snowpack that are worth mentioning. 

  1. 2/25: At the base of the most recent snow this interface may contain surface hoar, graupel, or a thin crust depending on aspect and location. If avalanches fail at this layer they may trigger easily and propagate widely. 
  2. 2/23: The frim crust formed during the atmospheric river may extend up to roughly 5800’. This snowpack marker can serve as a way to delineate recent storms. 
  3. Mid-January: The facet-crust layer from mid-January continues to lurk 5-8’ deep in the snowpack. The last avalanches occurred on this layer Monday at Crystal Mountain and likely in the Goat Rocks Wilderness. Very little information is known about the current condition of this layer or its grains. 

In addition to these potential weak layers, cornices grew very large and overhung during this stormy period. Give these giants a healthy amount of space. This includes staying out from under slopes where they loom above. 

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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