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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Out of date — this forecast expired 5 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

Recent very large and unpredictable natural avalanches should give you pause and make you think twice about entering large start zones, avalanche paths, or their runouts. These slides are running far distances toward valley bottoms and are most likely unsurvivable.

Avalanche problems

  • Deep Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    3

    Very large and deadly natural avalanches continue to occur around the state, including multiple slides reported over the weekend in the West South. Many of these avalanches are suspected to have run on the Mid-January crust/facet combo, which has recently been measured close to 7 feet deep (200cm). Although not all of the recent avalanches are confirmed on this layer, they have all been big enough that if you were caught in their path you probably would not survive. The threat of these unpredictable avalanches should be what shapes your decision-making and terrain selection. Many of these slides have run very far distances and broken trees as they descend. Know that if you decide to enter large start zones, avalanche paths, or runout zones, that you are putting yourself at risk.

    (2/28/2021) This slide on Norse Peak was measured to be over 1000' wide and approximately 6 feet deep. It broke trees and is suspected to have run on Friday (2/27)

  • Wind Slabs

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

    You could still encounter Wind Slabs at upper elevations on Tuesday around the West South. In addition, cornices have grown large and over-hung recently and may continue to develop. Give these beasts a wide berth and look for the slopes below them to contain Wind Slabs. You can also look for actively blowing snow, textured snow surfaces, or smooth pillow-like piles of snow to help you identify wind-loaded features to avoid. Wind Slabs are generally found on leeward slopes near ridgelines or near rocky features such as the base of cliffs or sides of gullies.

    (2/28/2021) Winds have been strong enough in the West South recently to load leeward slopes and build large cornices. These cornices could act as triggers on the slopes below.

Avalanche Discussion

On Sunday, NWAC team members reported multiple new very large (D3+) avalanches in the Crystal Mountain backcountry. One slide on Norse Peak was suspected to have run on Friday (2/26) and was measured to be over 1000’ wide and 6 feet deep. This slide broke trees and ran a far distance as it descended. Another slide in Cement Basin was suspected to have run on Saturday on the Mid-January crust/facet combo. We have vague reports of another slide on Sunday, but that has not been confirmed. These slides come only a few days after other very large slides had been reported in Union Creek and within the Crystal Mountain Ski Resort boundary. On Monday, a very large natural avalanche occurred at Snoqualmie Pass and similar avalanches have been occurring all week at Stevens Pass (see their forecasts for details). We have had at least one very large (D3+) avalanche almost every day for over a week throughout these zones and the Mid-January layer has plagued us the entire month of February. 

This unique problem and the amount of uncertainty around what it takes to trigger these slides is the reason for maintaining dangerous avalanche conditions and a unique avalanche forecast. You may notice that there is no avalanche problem listed in the below treeline band, but that it is rated as Moderate. This is not common practice for us. These slides may not initiate at lower elevations but are capable of running into them as we have repeatedly seen throughout this cycle, meaning that generally safe avalanche conditions do not exist.

Besides the deep and deadly, the snowpack has recently changed from cold and dry to moist due to rising freezing levels in many areas of the zone. Plenty of wet avalanche activity was observed and you could see this continue on Tuesday on slopes that see direct sunshine. At the highest elevations, slopes that do not see direct sunshine could still be holding onto some cold dry snow and some lingering storm instabilities. As we start to cool down, wet avalanche activity should taper and the moist upper snowpack should start to stiffen up as it freezes from the top down. This general cooling trend should help to stabilize the upper snowpack, but may not do much to help our deeper snowpack concerns. Stay safe out there.

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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