Boletín de aludes

Stevens Pass

Northwest Avalanche Center
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Peligro de aludes

Sat
Alta montaña
2 · Moderado
Límite del bosque
2 · Moderado
Bajo el límite
2 · Moderado
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Desactualizado: este boletín caducó 5 years ago. Estás viendo condiciones pasadas, no el boletín vigente.

Lo esencial

Be cautious around steep slopes facing the north half of the compass at both low and high elevations. If you get unlucky, you could trigger a large or surprising persistent slab avalanche. An incoming storm may increase avalanche danger later in the day, and shallow wind slabs near ridgetops may pose a threat.

Problemas de aludes

  • Persistent Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Possible
    Tamaño
    1.5–2

    There are spotty chances to trigger a persistent slab avalanche.  NW-NE aspects between 4,000 ft and 4,700ft are especially concerning because the weak layer is weakest here. This low elevation band has produced startling whumphs and shooting cracks in recent days. There is uncertainty with higher elevation, alpine terrain but expect that large and wide avalanches could be triggered from those areas as well, especially in heavily wind-loaded areas. Give big terrain features some space.

    The layer of concern can be found 1.5-2ft below the surface, and shouldn't be hard to identify. A thin crust sits over sugary faceted snow and sometimes surface hoar from late January. The bottom of this complicated structure is a stout crust, and makes a perfect bed surface for avalanches. Look for shooting cracks and listen for whumphing collapses as you move about- these are the snowpack's way of telling you it is unstable. There is a fair amount of uncertainty with triggering these tricky avalanches as the slab adjusts to warmer temperatures. Hold tight, it's not the time to venture into complex avalanche terrain quite yet.

    (2/1/2022)

    Very long shooting crack in a wind drifted slope on a north aspect at 4,000ft near Henry Creek. The slab failed in weak, faceted grains above a stout crust. The crack ran about 100ft long.

    Photo: Matt Primomo

  • Wind Slabs

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

    As a cold front approaches, winds should pick up to strong by the afternoon. Wind may drift the newly fallen snow into soft, reactive slabs as the day progresses. In general, the higher you go other more likely you may be to trigger small wind slabs. Look for direct signs of instability as you travel such as wind blown snow and shooting cracks. Unfortunately, we have more than just new snow avalanche problems. If you trigger an avalanche in the new snow, it could step down to a deeper weak layer and become a larger and surprising avalanche. You could also trigger persistent slab avalanches in wind drifted snow from the past week.

    Example intense wind blowing snow that could quickly create wind slabs.

    Photo: Shane Robinson

Avalanche Discussion

The storm didn't pan out for much of our mountains on Thursday, so avalanche danger was lower than expected. Observers noted around 3" of new snow, and warm temperatures really began to have an effect on snow surface conditions. Rollerballs and moist, sticky snow was found up to about 4,500ft. Favorable bonds have been noted with snowpack tests, and explosive testing on East to South facing terrain at Stevens Pass in the 4,800 to 5,000ft range produced no results. These are all good signs regarding the persistent slab problem we are monitoring. Storm totals since the 30th are around 25" and counting. Earlier in the week, winds were consistently from the west, and created thicker drifts with the snow from the 30th. Observers reported shooting cracks or whumphing collapses on northerly aspects in the low 4,000ft elevation band (Stevens Pass proper, Yodelin, and Henry Creek clearcuts). Uncertainty continues with upper elevations, as not many folks have been out on the higher peaks of the zone. 

Prior to recent snowfall, near-surface facets and surface hoar were found to have survived on a variety of shaded, northerly slopes below 4,700ft. Sunday's warm temperatures and mixed rain/snow may have melted these weak layers in some areas at mid-elevations, but perhaps not all. Approach the backcountry with an assessment mindset and be ready to stick to lower-angled terrain. Check out the other recent observations from Henry Creek, Upper Nason creek, Stevens Pass sidecountry, Jim Hill, and the Yodelin area. Let us know what you find, and if you experience whumphing collapses or shooting cracks to better track these tricky conditions. 

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