Bollettino valanghe

Olympics

Northwest Avalanche Center
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Pericolo valanghe

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2 · Moderato
Limite del bosco
2 · Moderato
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In sintesi

Warming temperatures will increase the danger on Sunday and will add some uncertainty. Let the upper snowpack guide you: If you find evidence of surface crusts breaking down or wet or sticky snow in wind-sheltered areas, plan to stick to simple or lower-angle terrain.

Problemi valanghivi

  • Loose Wet

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

    With Sunday's warm-up, we're uncertain how prevalent the avalanches will be. Wet loose avalanches may be isolated at elevations and aspects where the snow surfaces don't warm sufficiently. You can easily manage this uncertainty by looking for signs of instability; Watch for fresh avalanches, rollerballs and moist snow surfaces that slide easily. Your primary concern should be on SW-S-SE aspects exposed to direct sunshine.

    The breakdown of crusts, rollerballs, or 6" or more of slushy snow are all good indicators that conditions are changing rapidly and to move away from steep slopes. 

    Example: Numerous rollerballs are a sign the upper snowpack is destabilizing.

    Photo: Payton Schiff

Avalanche Discussion

Following a period of mostly below-freezing weather, the Olympics warmed above freezing on Saturday. Hurricane Ridge is expected to stay above freezing for much of the next week.  How the late November solar radiation + warming react with cold snow surfaces and thin crusts is difficult to predict. Your powers of observations are your best tool to staying safe. If you see something unusual, adjust your travel plans to seek simpler terrain.

On Saturday, ONP rangers encountered a friable crust that was breakable on sun-affected aspects. Shaded aspects had 1-1.5 cm surface hoar above a thin, breakable crust with 3-4" of ski penetration and high-quality riding still on these aspects. The Underlying crust will limit the size of avalanche activity.

A slab avalanche in the Mt Rainier area on 11/30 illustrates the potential for increased cornice fall. These cornices are a hazard in their own right, but they can trigger older wind slabs or wet loose avalanches on the slopes below. If you see overhanging cornices, give them extra space on the slopes above you.

Hurricane Ridge weather station has 32" of total snow depth, a healthy november start! Maggie's snow stake recorded 40" on 11/27. The wind events of mid-November created cornices on atypical aspects and also filled in forested areas. There is enough snow for avalanches to run above around 4,400 ft, but minimal coverage below that elevation.

On Friday, ONP Rangers found crusts on most sun-exposed aspects. They got a failure in column test about 14" down that we don't think is concerning at this time. This layer is worth monitoring, but with a cool start, light winds, and no precipitation, the layer is unlikely to be stressed.

On Wednesday, ONP Rangers found widespread surface hoar resting on near-surface facets in most locations that are at all sheltered. On sun-exposed aspects, the weak surface grains rest on a crust, while on shaded aspects, they found about 3" unconsolidated dry snow. The remainder of the snowpack consists of decomposing fragments down to melt forms sitting on the ground.

If you get out tomorrow, consider submitting an observation on the NWAC Avy App or here.

 

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