Bollettino valanghe

Olympics

Northwest Avalanche Center
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Pericolo valanghe

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

In sintesi

Small avalanches may bond poorly to or propagate more widely than you expect on a crust complex. Slabs will focus on the lee sides of ridgelines, beneath fresh, sharp cornices and in areas of active blowing snow deposition. Consider lower angle entries off ridgelines if you suspect drifts of 6" or more.

Problemi valanghivi

  • Wind Slabs

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

    Wind slabs will build in a hurry Friday morning as light to moderate ridgeline winds redistribute snow as it falls. Although we're only expecting 3-4" of snow, it should come in cold and easy to transport. It will also overly a firm crust on W or S aspects and a trap crust on N and E aspects.  The lower density snow sandwiched in this trap crust on N and E aspects may enhance propagation of any slab layer. Ease into ridgeline features, choosing slopes less than 35 degrees where you expect more than 6" of snow overlies the crust. These "poppy" slabs are more likely to knock you off your feet and into terrain where you didn't intend to venture. Pay particular attention above cliffs, or funnel-like terrain traps where a small avalanche could bury you. Cracking snow surfaces lets you know that a slab may want to propagate on the crust.

    Example: Shooting cracks in wind drifted snow. 

    Photo: Joe Dellaporta

Avalanche Discussion

ONP Rangers traveled in the Hurricane Hill area of Hurricane Ridge on Thursday.  With temperatures rising to 49F(!), melt-freeze (corn) conditions developed on aspects directly facing the sun. By the end of the day, we'll have firm crusts on W and S aspects. However, on N and E aspects, a breakable crust sits on 1/4 inch of cold dry snow over a firmer 1/2" supportable crust. 

As we watch a quick-moving storm bring new snow and wind redistribution, the interplay between slabs and the underlying crusts should be on your mind. It's a great day to use hand shears and investigate the bond with these crusts and also to evaluate the cohesion of the overlying slab.

The ONP Rangers also investigated several other weaknesses in the snowpack. They found two layers that sheared off with a shovel (around 14 and 22 inches down, respectively), but these layers did not fail in compression tests. The snow overlying the solstice crust failed progressively on hard taps 30" down at a grain size interface. This layer is not believed to be of concern at this time.

Ample snow cover makes for easier travel above 4000', however near this elevation, holes, creeks, and other obstacles quickly impede easy navigation. 

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