Bollettino valanghe

East Slopes South

Northwest Avalanche Center
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Pericolo valanghe

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

The avalanche danger will be highest at upper elevations where slabs may become large and on shaded aspects where slabs could propagate widely on a weak snow interface. Avoid wind-loaded slopes steeper than 35 degrees and don't try to nuance the problem on Sunday.

Problemi valanghivi

  • Wind Slabs

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

    Wind slabs will be growing larger with elevation and time as moderate winds transport 4-6" of snow. Slabs may be sensitive, widely propagating, and surprise you. A cold storm arriving Saturday night and continuing on Sunday will load wind slabs onto potentially poorly bonded interfaces. Shallow, cold, dry, and faceting snow along with isolated surface hoar existed on shaded aspects prior to the storm (see the photo gallery). Crusts formed on sun-exposed aspects as of Saturday. Use your terrain selection rather than slope tests or pit results to avoid a challenging wind slab problem on Sunday. Shooting cracks, whumphs, or active wind loading are all warning signs. Avoid all wind-loaded slopes steeper than 35 degrees, particularly slopes below growing cornices or in areas where you find more snow above the 2/19 crust.

    At lower elevations, slick crusts remain the primary hazard, but pillow-like drifts could still form avalanches that knock you off your feet.

    Example: Fresh, shallow wind slabs were easy to trigger on test slopes around the WN zone on Saturday and similar conditions may arise in the ES zone on Sunday.

    Photo: Jason Speer

Avalanche Discussion

We're expecting 4-6" of snow through Sunday with moderate SW and W winds redistributing and bonding poorly to old snow or crust interfaces. Typical tools you use to evaluate slab reactivity may not give you a full picture of the new/old interface and it would require many tests on a variety of slopes and aspects to get a more complete picture of what's out there. 

We've had more boots on the ground than typical the last two days, giving us increased confidence that your attention should be focused on the 2/19 crust and above. NWAC forecasters around Naches Pass in the NW part of the ES zone found a drastic increase in snow depth around 4800 ft with colder, drier snow near the surface at that elevation as well. NWAC forecasters also traveled near Bumping Lake on 2/25 (further east in the center of the zone), where firm crusts were on the surface up to 4500 ft. Although temperatures rose above freezing up to 6000 ft, shaded aspects stayed cold and 1-2" of faceting dry snow transitioned 4-6" by 6000 ft. In this location, minimal avalanche hazard exists below 5500 ft due to a stout slick crust near the surface. Wind slabs from an E wind event following the 2/19-2/21 storm were far more noticeable on generally W-facing aspects near Naches, suggesting the variable nature of the E winds through the terrain. These slabs were stubborn and should not be a primary cause for concern moving forward.

Let us know what you see by submitting a public observation. 

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