Bollettino valanghe

West Slopes Central

Northwest Avalanche Center
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Pericolo valanghe

Tue
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
1 · Debole
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Non aggiornato — questo bollettino è scaduto 4 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

Downwind slopes will still hold day-old and maybe even new slabs of wind drifted snow. Identify and navigate around steep wind loaded features on lower angle, planar terrain. Move off and away from steep, sunny slopes where you see signs of wet avalanche instability like rollerballs and pinwheels.

Problemi valanghivi

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–1.5

    As the current crop of shallow wind slabs gains strength, the place where you can trigger one becomes more isolated. If you do trigger a slab avalanche on Monday it will most likely be on a convex rollover, a gully wall, or around a cliff or rocky outcropping. These are features where wind slabs are often more tenuously perched on the slope and have less support from the terrain below. 

    Tune into the pattern of wind loading by using scoured snow surfaces, cornice-like features, and changes in snow texture to figure out where wind slabs might lie in wait. Use small test slopes to get a read on how the new snow is reacting to your weight. Small hand pits can give a sense of how wind slabs are bonded to the layer below. Active wind loading is not likely but be on the lookout if westerly winds are stronger than forecast.

    An example of a human-triggered avalanche on a very steep, convex, wind loaded feature.  A person triggered, was caught and partially buried in an avalanche on nearly the same slope Sunday.

    Photo: Adam Ü

Avalanche Discussion

While the sun played hide and go seek Sunday along the west slopes of the Cascades, more sun is expected Monday after a round of early morning snow showers. Widespread wet loose activity is not expected but as usual, keep an eye on terrain overhead that is warming in the sun and producing rollerballs or very small loose wet avalanches. You may find more extensive wet avalanche activity south of Hwy 2 due to more new snow in that portion of the zone

Most avalanche observations on the west slopes revolved around shallow wind slabs that had developed in the last 24 hours. They tended to be stubborn, small, and shallow at 6" deep or less. To the north reported avalanche activity consisted of a single human triggered avalanche (D1.5) on a very steep, unsupported feature in wind loaded terrain (north @ 5000'). The rider was caught and partly buried in the terrain trap below. No injuries were reported.

It appears West Central got the least precipitation and new snow from the latest storm compared to zones to the north and south. While most areas on the west slopes picked up 6” or more of new snow, a majority of West Central and also Stevens Pass came in below average with 2-4” at treeline. The southern third of the zone may have fared a bit better as Alpental recorded 0.5” of precipitation and 10” of snow at upper elevations. 

A weak snow surface of light-density new snow, surface hoar, and facets was observed prior to the latest storm. Observations Saturday point toward these surfaces being warmed up and then destroyed by the wind prior to new snowfall. In areas where weak snow survives (sheltered, shaded slopes near treeline) and is buried intact, you could find new slabs that are easier to trigger or release in surprising ways. Identify and investigate the interface between new and older layers and ease into steeper terrain by starting with smaller, less consequential slopes.

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