Boletín de aludes

Stevens Pass

Northwest Avalanche Center
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Peligro de aludes

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

Lo esencial

Shallow storm slabs and sluffs may be easily triggered in the new snow, but larger surprising slabs may release from unsuspecting areas. Be wary of any steep slope facing the north half of the compass, even at low elevations. Listen for whumphing collapses, check for sugary facets beneath the storm snow and stick to lower angled slopes while new snow and wind may stress persistent slabs.

Problemas de aludes

  • Storm Slabs

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

    You could find a number of new snow avalanche problems on Thursday. Moderate snowfall with a gradual warming trend is likely to create shallow storm slabs. Wind may drift the newly fallen snow into soft, reactive slabs. Expect the new snow to sluff easily from steep slopes. These shallow avalanches could pack a punch in consequential terrain. Look for direct signs of instability as you travel such as recent avalanches, 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 deeper persistent slab avalanches...see below.

    Example shallow storm slab.

    Photo: Dallas Glass

  • Persistent Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Possible
    Tamaño
    1.5–2.5

    Plan your day to avoid steep open slopes at all elevations, knowing that you could trigger a large and surprising avalanche in some areas. Give large slopes a wide berth, even open gladed terrain. 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 consistently 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.

    The layer of concern can be found 1.5-3ft 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. We're in the incremental loading phase, where each day another round of snow and wind may make these tricky avalanches more likely to be triggered. Hold tight, it's not the time to venture into complex avalanche terrain.

    (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

Avalanche Discussion

We're in the pattern of 'incremental loading', where some new snow and wind are adding to the slab resting over a tricky facet/crust sandwich layer from late January (1/30). Thursday marks a bump in avalanche danger as we could pick up another 6-10" through the day. Storm totals since the 30th are around 21" and counting. Winds have been consistently from the west, and stripping and loading has been noted in many areas. Observers have reported shooting cracks or whumphing collapses on northerly aspects in the low 4,000ft elevation band (Stevens Pass proper, Yodelin, and Henry Creek clearcuts). At some mid elevations, observers have found the recent snow to be fairly well bonded to underlying rounded facets. Uncertainty continues with upper elevations, as not many folks have been out on the higher peaks of the zone. Be sure to step off the beaten track and make your own observations once in a while.  

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 recent observations from Henry Creek, Upper Nason creek, Stevens Pass sidecountry, Jim Hill, and the Yodelin area. Let us know if you experience whumphing collapses or shooting cracks to better track these tricky conditions. Check out the new snow climatology which came out on Tuesday.

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