Lawinenlagebericht

Stevens Pass

Northwest Avalanche Center
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Lawinengefahr

Fri
Hochgebirge
3 · Erheblich
Waldgrenze
2 · Mässig
Unterhalb
2 · Mässig
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Kernpunkte

07:30 AM update: Switched the problem order to prioritize wet loose avalanches over wind slab.

Wet avalanche problems should be forefront on your mind, but dry avalanche problems remain an overlapping concern. When in doubt, stick to simple lower-angled terrain to reduce the risk of triggering an avalanche. Use extra caution through the weekend as the Cascades see the first big warm-up of the year.

Lawinenprobleme

  • Loose Wet

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Likely
    Größe
    1–2

    Sunny and unseasonably warm weather arrives on Thursday. Dry snow often doesn’t play nice with sun and temperature-induced warming.  Cool easterly winds may not be enough to keep the wet avalanche activity in check. You need to evaluate the conditions where you travel and adjust your plan as necessary.

    Avoid travel on or directly under steep slopes where you see signs of instability, like rollerballs, pinwheels, or small avalanches. Wet, sticky snow is a key observation that slopes around you are becoming unstable. Wet loose avalanches can sometimes pull out a slab lower on the slope.

    (3/12/2024)

    Recent wet loose avalanche activity on the south side of Lichtenberg.

    Photo: Lyle

  • Wind Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    1–2

    A wind shift to the east will change up the pattern of recent wind loading. Expect to see dry, loose snow on northerly and easterly aspects drift onto leeward or cross-loaded slopes. Another factor is the reported avalanche activity on Wednesday (see discussion). Drifting snow could add even more load to the interface behind these avalanches.

    For now, it might be wise to just steer around steep terrain holding freshly drifted snow. Blowing snow should show you exactly which slopes are loading up.  Slope cuts and other simple tests can tell you about the reactivity of fresh wind slabs - but won’t do much when it comes to evaluating buried weak layers that might not be found until farther down the slope.

    While wind slabs are the prime concern, don't discount the 1-2' of new snow in more wind-sheltered terrain, especially where a slab is residing over a weaker facet-crust combination. Don't ignore obvious signs of instability, like shooting cracks, whumps, and recent avalanches.

    (3/4/2024)

    Dense, wind-drifted snow is often just below ridgeline. 

    Photo: Joe Dellaporta

  • Deep Persistent Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Unlikely
    Größe
    2–2.5

    The likelihood of seeing a large avalanche releasing in a deeper layer is becoming less as it gets more buried and gains strength. On the other hand, a large trigger like a smaller avalanche or falling cornice might be just the ticket to get one.

    Avalanches that run on deeply buried weak layers could be 3-4ft or deeper and can propagate widely across the slope. You won't get signs of instability before triggering one, as the layer is too deep. Your best bet is to remain aware of the terrain around you, staying out of complex alpine terrain and off of steep, unsupported, or wind-loaded slopes.  

    The weak snowpack structure has been slow to gain strength. You can find a thin layer of softer facets over a hard crust, about 3.5-4.5 ft below the surface. This layering (and the likelihood of triggering avalanches) is most pronounced at upper elevations (above 5,800ft) and further east in the zone. 

    (3/5/2024)

    A large rider triggered deep slab on a W aspect of Jim Hill at 6,500ft. 

    Photo: Nate Hough-Snee

Avalanche Discussion

Since Saturday, March 9th, Stevens Pass has picked up 1.71” of precipitation, with one inch of that falling in the last 48 hours. Strong winds have redistributed snow onto leeward aspects with signs of transport observed in wind-affected areas. A shot of sun on Tuesday morning helped kick off a round of small wet loose avalanches on southerly slopes on Lichtenberg. 

There were three notable slab avalanche observations in the last few days. On Wednesday, two separate skier-triggered avalanches were reported. One was observed to have failed at a surface hoar layer over a crust. Both were about 12” deep, and one was triggered remotely. Also, a large natural avalanche was reported on a heavily wind-loaded, east aspect around 5000’ just outside of the Steven Pass Mountain Resort boundary. It probably occurred overnight on Monday.

The Cascades are heading into a stretch of very warm sunny weather. It will be the first big, spring-like warming event of the year, with high temperatures in the 50’s and freezing levels over 10,000’. Very warm conditions through the weekend could produce significant slab and loose snow avalanches. 

As with any warming event, there is a high level of uncertainty as to where, when, or even if this scale of avalanche activity will occur. On the other hand, big natural avalanches aren’t really the kinds of things that should be taken lightly. It’s worth noting that smaller wet loose or wind slab avalanches, cornice falls, or snow shedding from cliffs can provide the trigger needed to pull out a very large avalanche. When planning for the weekend, consider that this is one of the times when an ‘improbable’ avalanche might actually occur.

Your avalanche, snowpack, or weather observations are extremely valuable to the avalanche community. Help create a more accurate avalanche forecast by submitting your observations here. 

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