Bollettino valanghe

West Slopes Central

Northwest Avalanche Center
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Pericolo valanghe

Sun
Alta quota
4 · Forte
Limite del bosco
4 · Forte
Sotto il limite
3 · Marcato
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Non aggiornato — questo bollettino è scaduto 4 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

Avoid traveling in avalanche terrain Saturday. Heavy precipitation and rising snow levels will make for natural avalanches that can run long distances. If you do go to the mountains prepare for rainy, stormy weather and challenging travel conditions in thick, wet snow.

Problemi valanghivi

  • Wet Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Very Likely
    Dimensione
    1.5–2.5

    The recipe for large natural avalanches Saturday is pretty simple: 

    • Significant precipitation with 24-hour totals of 2-3”
    • Warming and snow levels rising from 4000’ to 6500’ or higher by Saturday afternoon
    • Strong winds transporting large amounts of snow at upper elevations
    • A dry, weak snowpack that will likely fall apart under heavy loading and rain

    Avalanche problems will shift through the day at different elevations. Storm slab, wind slab, loose wet, and wet slab avalanches will all occur in some way or another. But the travel advice is the same - just avoid being on or under avalanche terrain.

    Natural avalanches, particularly wet slabs, are not the kind you can tiptoe your way around. You are either in the way or not. Below treeline areas with less snow cover will probably not produce numerous large avalanches. Smaller loose wet avalanches will still occur on most steep slopes.  Be aware of avalanche terrain overhead.

    An example of a wet slab avalanche from a rain event a few winters ago. They are often found in unusual locations. It's also difficult to predict the timing of when they will occur during a rain or warming event.

Avalanche Discussion

In the southern portion of West Central, there may be a layer of ice capping the snowpack. This may delay the timing of natural avalanches but it will likely break down at some point at which rain will weaken drier snow below. Either way a freezing rain layer on top of upside-down snow will only further complicate mountain travel.

Observers in West North reported endless signs of instability Friday including test slopes and small avalanches that were easy to trigger, hand shears test failing upon isolation, and upside-down snow. A few natural and human triggered, smaller slab avalanches were reported in wind loaded terrain. Small loose wet avalanches were seen below treeline where rain was falling on dry snow.  No large natural slab avalanches were noted but it’s probably just a matter of time given the weather forecast. Thick new snow and wind slabs over lighter snow made for slow travel. No freezing rain or surface crust was observed around Heather Meadows. Other areas may have fared differently. 

The wet, warm and windy storm made for quite the letdown after weeks of cold dry snow not usually found on the west side of the Cascades. The downside of these glory days was being left with a weak, layered snowpack. Only a few avalanches failing in one of many layers of facets or buried surface hoar were reported. But the weak structure is there and could be provoked as snow levels rise and precipitation intensifies.

 

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