Avalanche forecast

Snoqualmie Pass

Northwest Avalanche Center
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Avalanche danger

Fri
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
3 · Considerable
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Highlights

Dangerous avalanche conditions are expected on Thursday as winter weather impacts the zone. Triggering an avalanche will be more likely on slopes over 35 degrees or during periods of heavy snow and/or wind. That should be most of the day, so your best bet is to stick to simple terrain until this storm has wrapped up.

Avalanche problems

  • Wind Slabs

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

    The winds are strong with this one. Actively blowing snow, new cornices, or fresh drifts are all visual clues that can help you identify wind-loaded aspects you’ll want to avoid on Thursday. Look for Wind Slab development on the leeward side of ridgelines or near rocky terrain such as the base of cliffs or the sides of gullies. If you suspect a slope to be wind-loaded, see shooting cracks, or encounter snow that feels firmer under your feet, head for simpler terrain under 35 degrees.

  • Storm Slabs

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

    Even in areas protected from the wind, you could find slabs that are reactive to human triggers. Fluctuating freezing levels, reported weak snow surfaces, plus a few crusts for snow to run on all point toward more widespread Storm Slabs. Use hand pits, uptrack tests, and small test slopes as you travel to look for a poor bond to the old snow surface or storm snow that has come in upside down (heavy snow over weaker snow). Similarly to the Wind Slabs, shooting cracks or whumpfing collapses are red flag signs that the snowpack is unhappy. If you notice any of these signs, a poor bond, or blocks of snow failing easily during your tests, avoid slopes over 35 degrees.

    (2/17/2023)

    Example: You should use quick hand pits to see how the new snow is bonding and if you can identify any interstorm layers of concern.

    Photo: Andy Harrington

Avalanche Discussion

A series of winter storms are set to impact the zone over the next few days, starting on Wednesday night. This first pulse will bring moderate snow showers and increasing winds during the daylight hours on Thursday, with up to a foot of snow anticipated. You should expect to encounter touchy avalanche conditions during the height of the storm, including the possibility of some natural avalanche activity. 

Widespread weak snow (surface hoar) was reported in the zone on Wednesday by NWAC forecasters and avalanche professionals. In areas where it persists and gets buried, slabs could break in surprising ways by failing above you, spanning long distances, or wrapping around terrain features. On slopes that see direct sunshine, you could find a subtle sun crust at this interface as opposed to buried surface hoar. While this could help prevent the surprising avalanches, it may present a good sliding surface for avalanches to run on or a different kind of poor bond, depending on how the storm rolls in.

Additionally, we are expecting a slight bump in freezing levels mid-morning that loosely coincides with the frontal passage. With low-density snow already in place from our last storm, this jump in temperatures could allow for some heavier snow to fall and create an upside-down layer before returning to colder and lighter snow in the afternoon. Combined with increasing winds in the afternoon and the possible poor bond mentioned above, you’re going to have plenty of interfaces to check for instabilities before committing to a slope.  

Last week’s storm snow is generally right-side up but still lacks a great bond to the underlying 2/25 interface. While we haven’t seen a lot of avalanches on this layer, we haven’t had much of a slab over it to this point. Thursday could start to change that, and although we suspect that most avalanches will occur in the new snow, slides down to the 2/25 interface are certainly not out of the question.

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