Avalanche forecast

Snoqualmie Pass

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Out of date — this forecast expired 5 years ago.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

Very large and unpredictable avalanches continue to occur naturally throughout the region and should drive your decision-making and terrain selection. Be leery of large start zones, avalanche paths, and their runouts. These slides are running far distances toward valley bottoms and would most likely be fatal to anyone caught in their path.

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, most recently at Snoqualmie Pass (see the discussion for details). Many of these avalanches are suspected to have run on the Mid-January crust/facet combo, which has recently been measured close to 10 feet deep (300cm). 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 of these slides.

    (3/1/2021) A very wide, very deep avalanche released from the east bowl of Chair Peak at some point between Sunday night and Monday morning (NE-E-SE 5800; HS-N-D3.5/R4-O). Photo: Bryce Hill

  • Wind Slabs

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

    The highest elevations may still be hanging onto some Wind Slabs or form newer slabs with a slight bit of snow and some wind in the forecast for Monday night. 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) Large cornices and wind-loaded slopes below them remain a threat. The cornices could also act as triggers for deeper instabilities.

Avalanche Discussion

On Monday morning, we received word of a very large avalanche that occurred on Chair Peak in the Alpental Valley. The slide happened sometime between 4:00 pm on Sunday and 8:00 am on Monday and has a crown depth estimated to be over 10 feet in the deepest part. This is the second time Chair Peak has produced a very large (D3+) avalanche in the past week. It also ran last Sunday night or Monday (2/21-2/22) during the most recent atmospheric river event. This morning, the debris was found to have overrun Source Lake and the berm, which is a popular picnic spot for skiers, snowshoers, and hikers. The slide may have been triggered by a cornice fall, but that has not been confirmed. It is confirmed that this avalanche broke trees and almost ran to its historical maximum as it descended. This previous weekend, similar avalanches occurred in the West South and on 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.

In other news, the snowpack around Snoqualmie Pass changed from cold and dry to moist over the weekend due to rising freezing levels and a little precipitation. Plenty of wet avalanche activity was observed and you could see some new rollerballs on Tuesday afternoon if the sun comes out. 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, 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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