Boletín de aludes

Stevens Pass

Northwest Avalanche Center
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Peligro de aludes

Wed
Alta montaña
2 · Moderado
Límite del bosque
2 · Moderado
Bajo el límite
2 · Moderado
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Desactualizado: este boletín caducó 2 years ago. Estás viendo condiciones pasadas, no el boletín vigente.

Lo esencial

Strengthening March sunshine is likely to be the focal point of instabilities on Tuesday. Moistening snow surfaces may lead to easily triggered loose avalanches on steep slopes that face E-S-W. Very large deep persistent slabs remain a low likelihood, high consequence problem to be aware of. For these, identify larger terrain features that you'll want to stay away from.

Problemas de aludes

  • Loose Wet

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Possible
    Tamaño
    1–1.5

    Direct sun and slightly warmer temperatures may create wet loose instability on steep slopes. You can anticipate this problem by considering your aspect vs. timing of when you might be on any given slope. Look for signs of instability, like small rollers falling out of trees or small fan shaped slides. Feel for moistening snow surfaces on slopes in the sun. You can use test slopes to check and see how any given area might react. These slides should remain small, but may be able to entrain more than you'd think, especially in larger terrain features. 

    Example wet loose avalanche from last season.

  • Deep Persistent Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Unlikely
    Tamaño
    2.5–3

    Heavy snow and wind loading from the last week stressed a weak snowpack structure. The weak layers consist of facets and crusts buried in early February or mid February. Avalanches have run on these layers and grow to become very large, as they're 3-4ft deep and can propagate widely across the slope. You won't get signs of instability before triggering an avalanche, as the layer is just too deep. Snowpack tests can identify these layers, but have become inconsistent from one slope to the next. You're best bet is to remain aware of the terrain around you, staying out of large complex alpine terrain and off steep unsupported slopes. 

    The problem mainly exists above 5,800ft and in larger, perhaps wind loaded features. Its become more difficult to trigger an avalanche on these layers now that the storm snow is settling out, but chances are still high enough that it warrants staying in the forecast. This problem is more pronounced further east in the zone and the east Cascades.

    (3/3/2024)

    A natural D2.5 avalanche on Jim Hill that likely failed Feb 28-29. The failure occurred on weak 1mm facets above the Early February Crust. The crown was about a meter (3ft) deep. 

    Photo: Matt Primomo

Avalanche Discussion

Stevens Pass picked up another 5-7" by Monday morning. The snow was very low density and only came with 0.3" of snow water equivalent. Dry loose avalanches were easily triggered in the morning, then settled out notably by afternoon. For Tuesday, expect warmer temperatures and more sun. The strengthening March sunshine may start to have more of an affect on snow surfaces. Plan your day to move away from slopes in direct sun, and keep checking for moistening snow surfaces as the day progresses. Since the 24th, the Stevens Pass area has received about 5" of water equivalent, and the snowpack gained 3-4 feet. 

At Skyline on Friday, forecasters found the early February crust not to be an issue for triggering avalanches on south-facing slopes around 5000ft. However, if triggered, a crust/weak layer, just below the February 24th interface showed a high potential for propagation.  A forecaster on Sunday found a D2.5 (large) avalanche on Jim Hill at 6,200ft, NE. It likely failed on Feb 28-29, and the failure was on weak, faceted snow above the Early February Crust. I went to Big Chief on Sunday and dug several pits on different aspects around 5700ft. I found inconsistent results, yet both facets above the Early February Crust and the 2/24 layer were noted and produced test results (compression, deep tap moderate-hard) in some of the pits. 

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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