Bollettino valanghe

East Slopes South

Northwest Avalanche Center
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Pericolo valanghe

Sun
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
1 · Debole
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In sintesi

During periods of active weather, weak layers in the snowpack need time to adjust to a new load of snow and wind. You can look for signs of instability such as cracking, collapsing, and recent slab avalanches but dig down into the snowpack even if you don't see any to investigate the layers within. The best way to manage avalanche hazard will be to simply avoid steep, open slopes.

Problemi valanghivi

  • Persistent Slabs

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

    A weak layer of surface hoar buried 1-2 ft deep has been showing fewer signs of reactivity, but new weather inputs can reinvigorate sensitivity. This problem will be most problematic in areas where the slab overlaying the weak layer is more cohesive. You're most likely to find this set-up in areas that received more new snow, elevations that saw previous warming, or adjacent to ridgelines where the wind has drifted snow into stiffer slabs.

    Persistent slab avalanches can break in surprising ways across terrain features. You up the chances for a perilous surprise if you choose to step out blindly into steeper, more consequential terrain. You may or may not see any signs of instability on the surface before triggering an avalanche so testing for the buried weak layers can reduce your risk. Surface hoar can be identifiable as a thin gray line in the upper snowpack and with snowpit tests. Ultimately, your best way to manage the problem can be to just avoid open slopes steeper than 30 degrees.

    (1/7/2025)

    No propagation on buried surface hoar in this pit but pulling the block away from the pit wall reveals the layer quite well.

    Photo: Payton Schiff

  • Wind Slabs

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

    Little snow inputs from Friday into Saturday night with strong-extreme ridgeline wind speeds keep wind slabs on the table for areas close to the Cascade Crest. Although small, these slabs may have trouble bonding to slick crusts, surface hoar, and faceted snow below. Anticipate wind-affected snow lower down on slopes than you might expect. It is unlikely, but you could trigger a bigger and more consequential avalanche at upper elevations where older, deeper wind slabs are overloaded by fresh slab formation and fail on weak layers below.

    Blowing snow will tell you where slopes are being freshly loaded. Cornices and hard, uneven snow surfaces will point you toward where wind-affected snow - new and old - can also be found. These areas are commonly just below ridgelines and in cross-loaded gullies. Shooting cracks, collapsing, and recent slab avalanches are clear signs that you should avoid steep, exposed terrain.

    (1/7/2025)

    Small rider-triggered wind slabs in the Superbowl. 

    (6800, ENE)

    Photo: Payton Schiff

Avalanche Discussion

Friday's storm underperformed and Saturday night's storm totals sure aren't anything to be chomping at the powder bit over. What we can glean from this weather data and older observations is that new and recent snow will be resting over a variable and oftentimes weak snowpack. Be suspicious of steep slopes where new snow has fallen and is being blown around. The larger and more cohesive the slab, the more likely it will be to trigger a persistent slab avalanche. Additionally, the previous lack of slab cohesiveness is what removed the persistent slab problem at middle elevations earlier in the week but after warm temperatures and rain on Friday, the slab could have consolidated and become troublesome.

We unfortunately can't give more specifics about snowpack conditions for this zone due to a lack of on the ground data. Your best strategy is to make like a forecaster and dig around on many aspects to look for weak layers and unstable test results. Be sure there is no buried surface hoar before high-marking or sledding on steep slopes with convexities and terrain traps. When considering the wind slab problem, be aware of terrain below you. A small avalanche that knocks you off your machine could carry both of you into hazards such as cliffs and trees. 

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