Bollettino valanghe

East Slopes Central

Northwest Avalanche Center
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Pericolo valanghe

Tue
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
2 · Moderato
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In sintesi

Be careful of steep south facing slopes in the middle of the day because loose wet slides may run if the sun is out. You could still trigger a windslab near and above treeline where recent drifts rest on a crust. Large persistent slab avalanches are becoming less likely, though the consequences of triggering one are high. These are most problematic in the north and western parts of the zone, such as the Chiwawa River drainage.

Problemi valanghivi

  • Loose Wet

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

    With fresh low density snow over a firm crust, warming temperatures and sun, wet loose avalanches could be your number one hazard on Monday. Expect these to happen on steep slopes that face toward the sun during the middle of the day, if the sun is out. Moist, sticky snow and rollerballs are good indicators that these could happen spontaneously. Time your travels to avoid steep south facing slopes in the middle of the day to avoid getting avalanched by a wet loose slide. 

    Example loose wet avalanche

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Unlikely
    Dimensione
    2–3

    Persistent slab avalanches are still on our radar due to a weak layer of sugary snow that sits atop an icy crust from back in early December. This structure is one that is responsible for many avalanche accidents in this area, and continues to warrant respect, even though the chances of initiating a slide have decreased to unlikely. It is the consequences of triggering a slide that are paramount, because it could easily be large enough to bury or kill you. These dangerous and surprising avalanches can catch even the most experienced backcountry travelers. The best way to stay safe is to avoid the type of terrain where you are most likely to trigger one. Keep your distance from slopes 35 degrees and steeper that are open enough and tall enough to produce large avalanches. Watch for obvious signs of instability like recent avalanches, whumphing collapses, or cracks shooting through the snow.

    Look for weak snow just above a thick melt freeze crust roughly 1.5ft to 3ft below the surface, above 5,000ft. We suspect this is more problematic in the northern half of the zone, and closer to the crest where the dry snow exists above these weak layers. The most dangerous slopes will be at the higher elevations, in steep unsupported and rocky terrain. Recent southwest winds may created stiff slabs in some of this terrain. As recently as the 27th observers performed snowpack tests that indicated propagation is still possible with this layer of concern. I found it to 3ft below the surface on an east aspect at 6,600ft in the Near Treeline band near Chickamin Ridge in the Chiwawa Drainage.

    Further south and at lower elevations a thick crust can be found near the surface, so these layers are not as concerning there. Here, shallower windslabs that rest over the most recent (12/21) crust will be your concern at upper elevations. Slabs will be deeper and widest in higher elevation, wind exposed terrain, and near ridgelines. Use test slopes to check how well recent slabs are bonding. As always, avoid wind exposed slopes steeper than 35 degrees if you find signs of instability or fresh avalanches. 

    (12/23/2020) A crown of an avalanche that ran between Dec 19-20th on a NE aspect near 7,000ft in the Alpine Lakes Wilderness.

Avalanche Discussion

About 4" of snow has accumulated in the past few days in the eastern half of the zone, but the higher peaks near the crest have received closer to 8". Previous surfaces were a mix of slick melt freeze crust, near surface facets or surface hoar, and wind packed particles. 

As is typical for the eastern slopes, there is a lot of variability in snowpack depth. Just east of the crest you may find 6ft of snow at 6000ft, but at  that same elevation east of Highway 97 in the Wenatchee mountains you may only find a few feet of snow on the ground. 

During the ongoing Covid-19 pandemic, continue to follow the latest guidance from local, state, and federal health officials. Avoid unnecessary risks that could impact first responders and stress medical resources. Wear a mask when appropriate, practice social distancing, and consider recreating closer to home.

Regioni coperte