Avalanche forecast

Snoqualmie Pass

Northwest Avalanche Center
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Avalanche danger

Mon
Alpine
3 · Considerable
Treeline
2 · Moderate
Below
2 · Moderate
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Highlights

Sunday will be the first round of a multi day storm cycle that should drive dangerous avalanche conditions. Once 6 inches of snow has piled up, start thinking about avoiding slopes over 35 degrees if you see signs of instability. Avalanches could break in surprising ways if weak snow surfaces are preserved and buried.

Avalanche problems

  • Storm Slabs

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

    Incoming snow and wind will bury a variety of snow surfaces on Sunday as we move into a stormy pattern that will increase avalanche potential over the next few days. Avalanches may act differently based upon the surface they fall on and the terrain’s exposure to wind. In some areas, you may see some surprising avalanches that break widely or connect terrain features, requiring you to dial your terrain choices way back. If you find that more than 6” of new snow has fallen, start to use small test slopes to see how the new snow is reacting to your weight, or use quick hand pits as you travel to see how it has bonded to the old snow surface. In areas that are prone to collecting wind-drifted snow such as the lee side of ridgelines or rocky chutes and gullies, slabs may be thicker and possibly stiffer. Identifying slab potential, seeing poor bonding in your tests, or noticing red flag signs of instability such as recent avalanches, shooting cracks, or whumpfing collapses should steer you away from steeper slopes over 35 degrees. 

    (2/20/2022)

    This slab was triggered by skiers in the trees below Pineapple Pass on 2/20.  Similar slabs may develop on Sunday with incoming snow.

    Photo: Public Observation

Avalanche Discussion

The existing snowpack at Snoqualmie Pass is considered to have a generally strong base with differences in the upper snowpack depending on aspect and elevation. Some of the existing snow surfaces are considered weak and capable of producing surprising avalanches on Sunday. We suspect most avalanche activity to involve the new snow, but can’t rule out isolated events down to the Valentine’s Day Crust. Here’s some more information regarding the intricacies of the upper snowpack:

  • On slopes that typically see direct sunshine, snow should be falling on a melt-freeze crust formed during sunny weather in the latter part of the past week. This crust will vary in thickness, and below it, a thin layer of weak snow (facets) may exist. Cold dry snow still exists between this crust and the 2/19 interface. 
  • On shadier slopes, this sun crust may not exist or could be more subtle. In its place should be settled storm snow from last weekend over the 2/19. On Saturday, widespread weak snow (surface hoar) was reported by Alpental Pro Patrol and recreationalists in these areas. It remains to be seen how much of this weak snow is preserved and buried on Sunday. It may become discontinuous across the landscape, but will be the most likely culprit for developing a poor bond and surprising avalanches.
  • As you ascend in elevation, the previous snow surface should be more wind-affected and possibly more irregular. Wind scoured surfaces, textured snow, or even stubborn Wind Slabs were all reported prior to this storm. Some of these slabs formed in unusual locations due to cold east winds.
  • The Valentine’s Day Crust is an easily identifiable interface that should be 1-1.5 feet below the surface. The more subtle 2/19 crust should be just a few inches above it. Both of these interfaces have confirmed weak snow associated with them. Our expectation is that Sunday’s snowfall will not be enough to see widespread action on these layers.

Temperatures should start to elevate as the day wears on, and could start to produce “upside-down” heavy over lighter snow, increasing avalanche potential. This same warm-up could bring some rain to lower elevations, initiating small Wet Loose avalanches for you to avoid on steep slopes. As we roll into Sunday night, more significant and warmer precipitation will be on our doorstep. This second round of precipitation should drive more dangerous avalanche conditions and could bring the deeper 2/19 and Valentine’s Day Crusts into play. Be on the lookout for weather changes that could indicate that this more significant wave is arriving earlier than forecast. Sunday night will not be an ideal time to spend camped out in the mountains.

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