Bollettino valanghe

East Slopes North

Northwest Avalanche Center
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Pericolo valanghe

Tue
Alta quota
4 · Forte
Limite del bosco
4 · Forte
Sotto il limite
4 · Forte
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In sintesi

Heavy snow, warming temperatures, and very strong winds will create very dangerous avalanche conditions on Monday. A natural avalanche cycle is expected to occur, and slides could be very large and destructive. Avoid exposure to all avalanche terrain, and be careful of roof avalanches from buildings.

Problemi valanghivi

  • Storm Slabs

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

    Up to three feet of snow is expected with a warmup through Monday. More new snow will fall, and temperatures will continue to slowly rise through Monday afternoon. Storm slabs will run naturally and could be very large. These won't' be your light and fluffy kind, they will be thick and dense. Very strong winds will blow, creating thicker and more reactive slabs in any exposed, open slopes. Slides could step down to become unsurvivable deep slab avalanches, and run to valley bottoms. Stay off of, and out from underneath avalanche terrain.

    Example large natural avalanche (D2) in motion.

  • Wind Slabs

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

    Very strong westerly ridgeline winds will continue to transport snow onto lee slopes. You'll find firmer wind-affected snow near and above treeline and even on open slopes well below treeline.  Shooting cracks or hollow-sounding snow are signs you could trigger an avalanche on similar nearby slopes.  Avoid going into or underneath steep open slopes. Cornices may begin to fail and trigger avalanches in alpine terrain on Monday as well.

    Example of active wind drifting snow. Notice the fracture near the edge of the wind lip, indicating touchy conditions.

  • Loose Wet

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    1–2

    At lower elevations, loose wet avalanches may begin to run naturally by the afternoon. These could grow to become large on steep slopes. Wet slides have the potential to run over common hiking trails and snowmobile trails in the zone below 4,000ft. Stay off of, and out from underneath any steep slopes if you notice rolleballs, or fan shaped avalanches. Roof avalanches may begin sliding off buildings on Monday. Stay aware of your surroundings and don't linger underneath a snow covered roof. 

    Example wet loose avalanche that ran over a hiking trail.

Avalanche Discussion

A big change is underway with the brunt of an atmospheric river entering the area Sunday night into Monday. A significant dump of heavy, wet snow is expected. Slowly rising temperatures, very strong winds, and heavy snow and rain will cause a natural avalanche cycle. Observers noted intense wind transport on Saturday and Sunday and we expect that to continue for the next 24 hours. 

Persistent slab avalanches are still on our minds in some parts of the zone west of Washington Pass and more recently in the eastern mountains. On Saturday an observed noted snow fracturing easily on a suncrust, others found shooting cracks, and others large dry loose avalanches. On Wednesday 2/17, an observation from the Twisp River drainage in the near treeline band found the mid-January facet/crust combo unreactive in snowpack tests and over 3 ft down.  Buried surface hoar slightly closer to the surface,  less than 3' or 80 cm down, showed sudden results in snowpack tests. Further west, the last persistent slab avalanche occurred near Rainy Pass on Feb 8th (see photo below). It is suspected to have run on the mid-January crust-facet layer about 2-3ft below the snow surface. This layer may begin also to 'wake up' in the next 24 hours.

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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