Bollettino valanghe

Olympics

Northwest Avalanche Center
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Pericolo valanghe

Mon
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
Senza grado
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In sintesi

Increasing winds and snowfall raise the risk of mostly small human-triggered avalanches. Anticipate and steer around drifts where 6" or more of snow above a crust intersects steep terrain. Use simple representative slopes and hand shears to evaluate the crust interface.

 

Problemi valanghivi

  • Wind Slabs

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

    Generally, light snowfall starts early Sunday above the 4000 ft rain/snow line while increasing moderate ridgeline winds and strong gusts redistribute that snow as it falls. Expect shallow slabs in isolated areas to start the day, transitioning to slabs up to size 1.5 by the end of the day. The specific terrain features where you might trigger a slab include start zones and mid-slope features, to the lee of fresh, sharp cornices and smooth lens-shaped pillows. Anticipate the problem and steer around slopes 35 degrees and steeper or convex rollovers. Slabs could be more touchy on NW-N-NE aspects where firm, punchy snow may overly lower density snow above a crust. On most other aspects, these slabs rest directly on the crust. In either case, the crust provides a good bed surface for the slab to run farther than you expect, so consider the terrain below you. 

     

    Example: A small human-triggered wind slab on a convexity. This was well off the ridgeline on a cross-loaded feature. 

    Photo: Shane Robinson

Avalanche Discussion

The temperature at Hurricane Ridge barely tapped and mostly stayed below 32F on Saturday, following daily fluctuations above and below the freezing mark since 2/16.  This marks the start of a cooler and snowier weather pattern for Hurricane Ridge. With that shift comes a transition to dry snow avalanche concerns. You may find more fresh snowfall in the western Olympics, and more previously dry snow available for transport on upper elevation N-facing aspects in the southern Olympics. If you travel in these areas, anticipate the possibility that dangerous avalanche conditions develop at upper elevations with the potential for larger wind slabs. Seek simple terrain if you encounter shooting cracks or drifts deeper than 10".

Observers in the Hurricane Ridge area found reasonable complexity to the upper snowpack on N aspects. Sunday's slabs will form above 1" of low-density snow (on NW-N-NE aspects) sitting above a 2" crust. You might also find a crust sandwich with some slightly weaker snow in between. The most notable layer is 2" of near surface facets above the stout 2/11 crust down 8" below the snow surface. Snowpack test results were unimpressive and these layers are somewhat protected by crusts closer to the snow surface. Mild temperatures on 2/23 flattened or melted off 5 mm surface hoar that existed on most aspects early Thursday morning (photo in gallery).  Where snow exists on W-S-E aspects, melt-freeze cycles have produced stout crusts to the surface. Bring sharps if you plan to traverse steeper terrain on these aspects.

We expect coverage to start increasing at lower elevations throughout the coming week. At some point this coming week, slopes will be rideable on SW-S-SE aspects and at lower elevations. However, on Sunday, any snow that falls below 4500 ft will fall on bare ground. Coverage remains particularly poor on the southern half of the compass, where patchy snow has mostly melted down to grassy surfaces and around 2-4" of snow expected on Sunday won't change that. Gullies might hold barely rideable snow in narrow strips due to wind transport. Throughout the terrain, numerous obstacles, including running creeks and open holes, can make it much more dangerous. Take it slow and give yourself time to deal with these persistent hazards. 

NWAC may issue a gray "No Rating" for an elevation band when there is not enough snow to present an avalanche hazard.

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