Avalanche forecast

Snoqualmie Pass

Northwest Avalanche Center
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Avalanche danger

Mon
Alpine
2 · Moderate
Treeline
2 · Moderate
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Out of date — this forecast expired 5 years ago.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

Despite the danger rating, the consequences of potentially enormous avalanches continue to linger. Limit your time in and around very large avalanche paths. This includes steering clear of places where avalanches may run and stop down near valley bottoms.

Avalanche problems

  • Deep Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    3

    Focus on the consequences rather than the likelihood when considering where and how you want to travel with regards to Deep Persistent Slabs. Any avalanche on this layer would be enormous, break trees, travel far distances, and likely be unsurvivable. Cooler weather, a strengthening upper snowpack, and a lack of avalanches over the last few days give us some hope. However snow profiles this week show the mid-January facets/crust largely unchanged. Significantly limit or even totally avoid traveling in larger avalanche terrain. This includes where these giant slides may run and stop down in the forest. 

    Assessing and forecasting deep slabs is inherently tricky. Many of our normal observations will not adequately represent the beast lurking 8-10’ beneath you. Conditions can “feel” stable right up until the avalanche occurs. This leads to a very high degree of uncertainty. Instead, focus on what you know. A significant weak layer exists in the snowpack, and very large and destructive avalanches occurred this week. Keep your conversation and decisions centered on these facts rather than potentially misleading surface observations.

    (3/6/2021) Here you can see many of our recent weak layers in the snowpack including the mid-January crust/facets. In this location it sat 7.5' below the snow surface. Kenall Lakes, 5000', S-asp. m=30, HS 420cm.

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1

    Shallow wind slabs may form along ridgelines and the sides of exposed features Sunday morning. Keep your eyes open for blowing snow and small drifts that could help you identify potentially wind-loaded terrain. Pay attention to slopes below cornices, near rocky areas, and in confined features where these thin slabs could trigger more easily. Don’t let these potential small avalanches surprise you and carry you over a cliff or into rocks. They could also serve as a trigger for the much larger and scarier deep persistent slab in bigger terrain.

    (12/22/2020) Example; This shallow wind slab occurred in a rocky confined feature earlier this winter.

Avalanche Discussion

On Saturday, NWAC staff found 3-4” of new snow at mid-elevations around the Pass. You may see an additional 2-4” by Sunday afternoon. The heaviest precipitation and strongest winds are expected in the morning hours, with less later in the day. The new snow bonded well to a thickening crust. In open terrain above 4000’, the crust could support the weight of a human. In treed terrain and at lower elevations the crust was too thin or even non-existent. This snow adds to a relatively strong and well-settled upper snowpack. 

While several layers exist deeper in the snow, the primary layer of concern remains the mid-January facets/crust. This layer sits 8-10’ below the surface. A snow profile by NWAC staff on Saturday found the facets showed signs of rounding but still remained weak. The last known avalanche on this layer occurred 2/28-3/1 on Chair Peak in the Alpental Valley. The slide descended more than 2000’, overran Source Lake, and traveled into the trees beyond. Slides like this and many others that reached valley bottoms should cause us all to evaluate our travel choices in light of this particularly unique avalanche problem. As result, the avalanche danger below treeline is not driven by a problem you can trigger, but rather by the chance for these giant slides to descend from above and impact travelers at lower elevations. 

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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