Avalanche forecast

Stevens Pass

Northwest Avalanche Center
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Avalanche danger

Sat
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
2 · Moderate
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Highlights

A storm will bring snow in the night which will continue through the day, with moderate to strong winds. Wind-drifted pockets of snow are where you're most likely to trigger an avalanche, so identify these textured or smooth thicker slabs which may actively be loading and avoid them on steep slopes. Although not likely, you could trigger a large and surprising avalanche on a crust buried around 2 feet deep, which may even happen well below treeline. If more snow or stronger winds than forecasted occurs, avalanche danger could be higher. 

Avalanche problems

  • Wind Slabs

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

    Two different types of wind slabs are on the menu Friday: new, shallower soft slabs and larger, thicker hard slabs. You're most likely to encounter shallow new soft slabs. The new round of snowfall is expected to come in as a couple inches overnight with a few more falling during the day. Moderate to strong easterly winds overnightare forecasted to decrease slightly and shift westerly by the afternoon. This will create soft, small new slabs. Expect some changes in slab distribution as the winds shift direction. Be on the lookout for active snow transport, and search for thicker pillows of snow. Steer around these fresher drifts in steep locations. Using hand pits and small test slopes is a good way to identify weaknesses in any small, shallow new wind slabs. If more snow falls or wind is different than expected the avalanche danger could be higher than forecasted. 

    A much lower chance exists of you triggering an avalanche in a large, old wind slab. Even if the odds are lower, if you trigger one of these your chance of getting buried and killed in one of these is much higher. Recent large avalanches have been reported on southerly aspects below treeline, and we've also received reports of whumphing collapses on northerly aspects near treeline. Steep, open, unsupported, and heavily wind-loaded slopes are where you're most likely to encounter this problem. For now, steer clear of these areas. Unlike with softer, shallower slabs, these deeper ones could catch you unaware, as you may not see any indicators like shooting cracks, and the large avalanches could break far above you. For assessment, you'll have to dig a pit to investigate crust interfaces in the top 1-3 feet of snow. If you observe whumphing or other red flags or find any weak interfaces in pits, these are obvious indicators to steer around steep nearby slopes. 

     

    (3/4/2023)

    Wind slabs on steep, convex rollovers like you might see on Friday. 

    Photo: Griffin M

Avalanche Discussion

Moderate to strong easterly winds were actively transporting snow through the pass on Thursday. This is expected to continue as snow begins falling overnight. A midday shift to moderate westerly winds may make it hard to identify where slab buildup is located. A crust, probably breakable, likely exists near the surface on steep south-facing slopes. It may be covered with a thin layer of new snow, and could make a good sliding surface for shallow new avalanches. 

Our concerns about deeper weak layers exist due to a few reports and followup investigations from recent days. A widely propagating avalanche was reported as remotely triggered by a skier on a SSW aspect at 4700ft at the start of the week. A nearby followup found a 3/1 sun crust buried about a foot down with moderate amounts of bonding to the overlying slab. The Valentine's crust sat deeper, at about 2 feet, and produced propagating results in tests. This is likely the layer the remotely triggered avalanche failed on. Observers also reported a whumphing collapse on a north-facing slope 5600-58000ft near the Swath. They identified the layer as a decomposing crust 80cm deep, which corresponds with the Valentine's Crust. A while back, on the 28th, two larger avalanches occurred which we suspect both failed on the Valentine's crust. One was triggered with explosives, (W, 4800ft), and another was the third rider on a heavily wind-loaded 5600ft SE slope. The slides were both large, D2s, failing 2-3ft deep. 

 

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