Bollettino valanghe

East Slopes Central

Northwest Avalanche Center
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Pericolo valanghe

Mon
Alta quota
3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
3 · Marcato
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Non aggiornato — questo bollettino è scaduto 6 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

A natural avalanche cycle is expected Saturday night into early Sunday morning with heavy snow and rain. Rain may seep into a previously dry snowpack up to 6,000ft and cause wet avalanches. Stick to lower angled terrain, and travel conservatively to avoid getting caught. 

Problemi valanghivi

  • Loose Wet

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    2

    Loose wet avalanches could be triggered or run spontaneously during the day. These could be large, and may gouge down to the early December crust. You will probably see evidence of recent activity if you look around at steep hillsides, as many naturals may run overnight Saturday into Sunday morning. Signs of loose wet instability are rollerballs, and wet sticky snow that entrains as it moves downhill. If you sink in deeper than your knee into wet snow, there is danger of deep loose wet avalanches on steep slopes.

    The best way to manage large loose wet avalanches is to avoid being underneath very steep slopes, even in forested terrain if the trees are spaced out. 

    Example large wet loose avalanche.

  • Persistent Slabs

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

    A natural avalanche cycle is expected overnight into early Sunday morning. Rain may filter down into a previously dry snowpack up to 6,000ft and cause wet slab avalanches. Above that, the snowpack may remain dry. In any case, the layers of concern are weak snow above or below a crust that can be found 16"-30" down in the snowpack above 5,500ft. 

    Persistent slabs dominate the way we travel and plan to travel in the backcountry because all slopes steeper than 30 degrees are suspect. They may fracture widely, and can be triggered from connected slopes below. On Sunday, these avalanches will be nothing to mess around with. If you manage to make it up to higher relevations on Sunday, keep it simple by staying well away from any steep open slope. Listen closely for whumphing collapses, and look for fracturing of large sections of snow. These are direct signs that the snowpack is unstable. 

    (12/18/2020) Part of a D2 persistent slab avalanche that was ~500ft wide and 15"-20" deep in neighboring Stevens Pass zone. The avalanche was unintentionally and remotely triggered by experienced backcountry skiers on 12/17. The avalanche ran on weak snow over the 12/9 crust.

Avalanche Discussion

This storm will be an impactful one for the snowpack with heavy snow for the alpine, and lots of rain on snow below that. There is a lot of variability in snowpack depth just east of the crest where you may find 6ft of snow at 6000ft, but east of Highway 97 in the Wenatchee mountains you may only find a few feet at the same elevation.  In any case, the December 9th crust is a prominent snowpack marker, and can be found at all elevations up to around 7000ft. Above this layer lies two potential layers of concern, a layer of facets just above the crust, and a thin layer of surface hoar a few inches above that. 

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.

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