Bollettino valanghe

West Slopes North

Northwest Avalanche Center
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Pericolo valanghe

Tue
Alta quota
3 · Marcato
Limite del bosco
2 · Moderato
Sotto il limite
1 · Debole
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In sintesi

Anticipate a tricky day with overlapping avalanche problems. You can trigger fresh slabs of new and wind-drifted snow, especially at upper elevations. Sun and warming could trigger a round of wet avalanches. Start your day and evaluate conditions in simple terrain before moving on to anything bigger.

Problemi valanghivi

  • Storm Slabs

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

    West North should see another good shot of snow overnight with another 6-10” by Monday morning.  In addition to the new snow, weak layering at the old snow surface and also above the Early February crust could increase avalanche likelihood. Observers found signs of instability related to these layers - but little in the way of actual avalanche activity - on Sunday.  The jury is still out . . . 

    As usual, you are more like to trigger a slab in wind-loaded terrain. However, 1-2’ of new snow is a good reason to be suspect of all steep slopes, wind-loaded or not. Unsupported features like convex rollovers are also great places to find slab avalanches.

    Don't ignore obvious signs of instability like whumphing, shooting cracks, and recent avalanches Hand shears and test slopes can help you gauge the bond of new snow layers. Be aware that slabs can become more reactive when they get their first hit of direct sun.

    (4/12/2023)

    Slab avalanches in new snow layers are possible until they've had a chance to settle and gain strength.

    Photo: NWAC Public Obs

  • Loose Wet

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–1.5

    The likelihood of seeing or triggering a wet loose avalanche will increase as the clouds clear out and the sun warms southerly aspects. Fresh snow loses cohesion and wants to slide down the mountain when warmed. There should be no lack of fresh snow by Sunday morning. A wet loose avalanche can trigger a slab avalanche lower on the slope.

    Rollerballs and pinwheels are signs that wet loose avalanches might not be far behind. Wet, mushy snow means it's time to get off and away from steep slopes that are destabilizing with sun and warmer temperatures. Anticipate a change in conditions as the sun comes out and keep track of what is overhead when it does.

    (3/17/2023)

    A wet loose avalanche on Slate Mt. in March 2023. Many wet avalanches start in steep rocky terrain like this.

Avalanche Discussion

Stay tuned into changing conditions and be ready to switch gears based on what you see. It could be one of those days when stability varies widely over a short distance due to spatial variability in new snow amounts, exposure to sun and wind, and snowpack layering,  You could find that conditions swing between quite stable to quite unstable over the course of the day. Take your time making and processing observations and pick less consequential or simpler terrain to reduce uncertainty.

Observers found a range of results regarding the most recent storm and wind slabs.  Hand pits yielded clean shears at the old/new snow interface, and the new snow cracked and fell apart with nearly every step in untracked snow. But test slopes produced few results, and shooting cracks were not common. One person triggered a 6” deep by 10' wide slab and took a short ride on a steep north-facing slope at 4700’. No injuries were reported.

Many out there found the moist, sticky snow was easy to push around on steep slopes. Rollerballs and and a few small wet loose avalanches were observed below 5000’. Other parts of the West North may have seen more extensive wet avalanche activity. Pan Dome at 5000’ stayed below 32F, but other 5000-6000’ weather stations saw temperatures above freezing for a good portion of the day. 

 

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