Avalanche forecast

Snoqualmie Pass

Northwest Avalanche Center
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Avalanche danger

Tue
Alpine
3 · Considerable
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Out of date — this forecast expired 5 years ago.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

Give the snowpack some time to adjust to the recent snow and rollercoaster weather before stepping into consequential terrain. Avalanches will be easier to trigger on convex slopes or near rocky features like confined gullies and the base of cliffs. If you see red flag signs of instability such as the snow surface cracking or recent avalanches, avoid slopes over 35 degrees.

Avalanche problems

  • Storm Slabs

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

    On Monday, you should look for heavy snow over lighter snow to help you identify areas where Storm Slabs exist. You can do this by using quick hand pits as you travel or feeling for density changes with your pole or foot. Shooting cracks or blocks or snow failing during upslope tests can give you an indication that the upper snowpack contains a slab. You may find that these slabs are thicker and possibly more reactive as you ascend in elevation or on open slopes away from tree cover. The most likely locations for you to trigger one of these avalanches are on convex or unsupported slopes over 35 degrees. Of course, areas where the snow was able to drift the snow into deeper piles near ridgelines or rocky features, such as gullies or the base of cliffs, will also have an increased likelihood of producing avalanches. If you suspect that the snowpack is unstable, seek out small test slopes to see how the snow is reacting to your weight. If any of your tests point toward slab avalanches or you are in doubt, default to slopes under 35 degrees.

    (2/20/2022)

    Reactive slabs were easily triggered by ski cuts and with explosives by Alpental Pro Patrol during their mitigation work. Take note of the layered slab and all the potential points of failure.

    Photo: Alpental Pro Patrol

Avalanche Discussion

Sunday’s weather panned out a little differently than anticipated, making for some tricky avalanche forecasting. NWAC forecasters on Kendall Peak found 16” of new snow on open slopes above ~4500 feet, with considerably less down in the trees. The snow was moderately well bonded to the underlying crust (2/19), but hand shears and small column tests repeatedly failed just above this interface. The storm snow is a bit layered and some mid-storm interfaces also failed easily during small column tests.  Shallow slabs on unsupported rocky slopes were observed to have failed naturally in the early morning hours, and a surprise appearance from the sun helped to trigger some Dry Loose and additional shallow slab avalanches on the upper slopes of Kendall Peak. In the next drainage over, Alpental Pro Patrol reported sensitive slabs triggered by ski cuts and explosives at the base of the storm snow during their control work. Avalanche Professionals near Silver Fir reported somewhat similar test results to those found by NWAC forecasters, but at lower elevations. As the sun warmed surfaces mid-day, storm snow that was initially fairly cohesionless and light started to “slab up” and consolidate.

On Monday, you need to continue to check all of the snow down to the Valentine’s Day Crust to see how the bonding and slab qualities are progressing before stepping into consequential terrain. It could vary greatly depending on aspect or elevation due to the variable surfaces observed prior to this storm or exposure to sunshine. Despite the return of snow, we are inching ever closer toward spring where the sun is stronger and the weather can be more erratic. We are expecting a general cooling trend as this storm winds down, but sun breaks could take the place of the departing clouds. The solar input could further consolidate the upper snowpack or produce some rollerballs and small natural loose avalanches on steep sunny slopes. If there are prolonged periods of sunshine, expect snow to fall from trees and rocks, or for freshly built cornices to fail. Be sure you are watching how the weather is changing the snow throughout the day and be prepared to alter your plans.

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