Avalanche forecast

Snoqualmie Pass

Northwest Avalanche Center
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Avalanche danger

Fri
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Out of date — this forecast expired 5 years ago.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

Just because the weather is nice does not mean that conditions are good to go. Recent very large and unpredictable avalanches have occurred in the zone, demanding that you take their consequences into account when choosing terrain.

Avalanche problems

  • Deep Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    3

    We continue to be concerned about the potential for very large natural avalanches in the Snoqualmie Pass zone. Recent avalanches, warm temperatures, and a known weak snowpack structure are all red flags that should have you thinking hard about your terrain selection. For the past week, very large avalanches have occurred erratically and are suspected to have run on the Mid-January crust/facet combo. This layer was measured by NWAC forecasters just over 10 feet deep on Wednesday, meaning that these avalanches will be very large, and being caught in one would almost certainly be fatal. The timing of deep slab avalanches is difficult to predict and we could go several days without seeing another deep slab release. On the flip side, it wouldn’t surprise us one bit to see multiple happen tomorrow. Know that if you decide to enter large start zones, avalanche paths, or runout zones, that you are putting yourself at risk. Many of these slides have run very far distances and broken trees as they descend, reaching valley bottoms and areas normally considered as “safe”.

    (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

  • Cornices

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2–3

    Continued high freezing levels and sunny weather may further destabilize cornices around the zone, causing them to collapse. The largest and freshest cornices may be found on east aspects, but take a look at what’s above you regardless of what aspect you are traveling on. If a large cornice falls, it could be the trigger needed for the deep persistent slabs we are concerned about. Even if the Mid-January crust isn’t activated, slab avalanches in the upper snowpack could fail or blocks of snow from the cornice breaking could descend toward you. This past Saturday, a cornice fall was responsible for triggering a large slab avalanche on Bryant Peak in the Alpental Valley. Cornices notoriously break further back than expected, so stay far away from them if you’re on a ridgeline. And keep off slopes that are below them.

    (2/27/2021) Thie very large avalanche was triggered by a natural cornice fall on Bryant Peak in the Alpental Valley. The resulting slab avalanche was at least 6ft deep. E, 5400' HS-NC-D2.5-R2-O Photo: Truc Allen

  • Loose Wet

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

    Thursday will be another day of warm weather and mostly sunny skies. Without a strong overnight freeze Wednesday night, it may not take as long for the snow to soften up and Wet Loose avalanches to occur once daylight hits. Look for these avalanches on slopes that see direct sunshine and to initiate at a point such as near rocks or trees. These slides can entrain significant snow, fan-out, and even trigger slabs as they descend downhill. Lower elevations that have gone through several rounds of freezing and thawing lately could have minimal or smaller avalanches, but upper elevations could now be reaching their tipping point to produce larger slides. Rollerballs and pinwheels, the snow surface getting warm and sticky, or snow shedding from trees and rocks will be your first indicators of Wet Loose avalanches. If you notice these signs or recent avalanches with fan-shaped debris piles, head for shadier slopes keeping aware of the terrain above you.

    (2/28/2021) Rollerballs and Wet Loose activity were observed on Sunday (2/28) in the Alpental Valley.

Avalanche Discussion

On Wednesday, NWAC forecasters and Alpental Pro Patrol were able to dig down to the Mid-January crust on a similar aspect and elevation to the Chair Peak slide that occurred on Monday morning. Although not a perfect comparison, we found the crust to be 10 feet (307cm) down from the surface and that weak snow did still exist in and around the crust. Keep in mind that even though the weather is nice, the snowpack continues to have a less than favorable setup, so don’t get lured into poor terrain selection. These avalanches are unpredictable and we have been very lucky to this point that most of the very large avalanches have happened outside of peak usage. Even though a deep persistent slab avalanche may not initiate at lower elevations, they are capable of running into them, meaning that generally safe avalanche conditions do not exist, even below treeline.

March often brings a bit of uncertainty for forecasters as longer days, stronger sunshine, and a transition from a cold winter snowpack toward a warmer springlike snowpack happens. When the snow starts to warm up, it generally starts to fall off of things. This means that cornices may fall and trigger slabs, or blocks of snow and ice may fall off rocks and cliffs to trigger avalanches on the slopes below. Even snow falling off trees and rocks may start as a simple snowball and grow into a large avalanche as it descends. This year, we are dealing with an additional layer of complexity to our springtime forecasting due to the deep persistent problem, giving us even more uncertainty than usual. Let this uncertainty and the consequences of these slides continue to guide your decision-making on what terrain is within your acceptable level of risk and 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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