Avalanche forecast

Snoqualmie Pass

Northwest Avalanche Center
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Avalanche danger

Thu
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
1 · Low
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Out of date — this forecast expired 2 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

You could trigger an avalanche in steep, complex, wind-loaded terrain above 4500’. Gullies, chutes, aprons below cliffs, and slopes that roll over and steepen are all prime locations. Look for textured surfaces, pillows, and lens-like deposits, and steer clear of steep, sustained slopes over 35 degrees if you observe these signs. Manage potential wet avalanches by moving to shaded slopes if you notice rollerballs, pinwheels, or moist snow surfaces.

Avalanche problems

  • Wind Slabs

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

    Fresh avalanches are the clearest sign of instability, and a natural wind slab in an extreme terrain feature released above Great Scott Bowl sometime between Monday afternoon and Tuesday Morning. Just a bit of new loading was enough to cause this slope to fail, showing that the 1/10 interface isn’t yet healed. You probably need to go into a rocky, steep, and loaded piece of terrain to find the problem. The age, hardness, and stubborn character of these slabs means that accurately assessing them for stability before you are on the slope will be challenging at best, or impossible at worst. Many or most slopes will be okay, but some will not.

    So what to do with this problem? The safest move is to choose a different type of slope. You can either use slope angle (more straight forward) to avoid this problem entirely by sticking to slopes less than 35 degrees, or you can choose simpler terrain (a bit more nuance required) that is planer, supported, low-consequence, and doesn’t show any signs of wind-loading. Banking on being able to assess slab reactivity for a problem like this is not a good approach.

    (1/14/2025)

    A natural D1 wind slab avalanche in  extreme terrain in the Alpental Valley. This slab released sometime between Monday afternoon and Tuesday morning. Avalanches like this are a sign that if you go hunting in steep, wind-loaded, and complex terrain, you can still trigger a wind slab avalanche on the 1/10 interface.

    Photo: Andrew Richardson

  • Loose Wet

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–1.5

    Warm overnight temperatures, the warmest day time temps of the week, and light winds could cause an uptick in wet loose activity on Wednesday. You may find a crust that will need to break down before this problem becomes an issue, or some slopes may not refreeze at all and could pose an issue soon after they see sun.  Luckily, this problem should give some clear advanced warning signs. Look for rollerballs, pinwheels, snow shedding from trees, moist or wet snow surfaces, and sinking in to wet snow past your boot tops. If you see any of these signs, stay off of and out from under steep slopes in the sun. You can shift your aspect to a shadier slope to mitigate this hazard.

    (1/14/2025)

    Rollerballs beginning to shed off steep slopes facing the sun. Wednesday will be the warmest day this week, with less wind and warm overnight temperatures to boot. If you see signs like this, there is the potential for proper wet loose avalanches.

    Photo: Andrew Richardson

Avalanche Discussion

This wind slab problem is a bit pesky. Depending on your location, a relatively hard slab between 8-24" deep sits above some soft and weaker snow over the 1/10 crust complex. This has been the failure point of the recent wind slab activity dating back to Saturday, including an avalanche that caused significant injuries. General reports from the field have been showing increasing stability, non-propagating test results, and a bond that is becoming more stubborn. But then, after two days without a reported avalanche, we received an observation of a natural wind slab that appears to have failed on the 1/10 interface. The narrow nature of the gully limited the destructive size of the slide, but the depth of crown was between 1-2' and the avalanche failed naturally. It's a single datapoint, but it's enough to tell you that you shouldn't trust this interface yet. 

Note the similar characteristics between this slope that failed and virtually every slope with reported activity. Complex, rocky, base of cliffs, confined gully or chute, below sharp ridgeline, cornice overhead... 

This is where this problem still exists.  Literally next to this recent slide, backcountry travelers in the Alpental Valley on Wednesday reported no signs of instability on steep, supported, and planar slopes, even where they saw signs of wind loading. These observations dovetail with what we have been seeing over the past few days. You can use slope shape and characteristics to decrease the odds of triggering a slide, even if you choose to travel on steep terrain. But if you venture into complex terrain like mentioned above, you can find the problem. Complex slopes are very typically wind-loaded, even if you don’t see visual evidence of the problem. This instability isn’t everywhere, which is why you will likely see folks using the very terrain we are warning about without incident, however, think hard about the level of risk you are comfortable with and consider the consequences of winding up on the wrong side of this problem.  Remember, there are lots of steep yet non-complex and supported slopes in this zone for you to play on.

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