Bollettino valanghe

East Slopes Central

Northwest Avalanche Center
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Pericolo valanghe

Fri
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3 · Marcato
Limite del bosco
2 · Moderato
Sotto il limite
2 · Moderato
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In sintesi

The Wenatchee Mountains and Icicle Creek areas could see over a foot of new snow overnight and into Thursday. In these favored locations, avalanche danger will increase significantly. It may be easy to trigger avalanches in steep terrain, particularly where the wind drifts snow into stiff slabs. Choose low-angle slopes sheltered from the wind to avoid getting caught in a large avalanche.

Problemi valanghivi

  • Wind Slabs

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

    As wind drifts fresh low-density snow into stiff wind slabs over weak, faceted surfaces or the slick Early February Crust (EFC) avalanches will likely become easy to trigger. To avoid triggering one of these wind slab avalanches, stick to slopes less than 30 degrees or travel on scoured ridgelines/slopes at mid and upper elevations. You can expect to find these slabs below corniced ridges, convex rolls, steep gullies, and at the base of cliffs. Actively drifting snow near ridgelines, fresh cornices, and deep pillow-like drifts are also signs to identify likely wind slab locations. The easterly wind direction could form wind slabs on aspects where you may not be used to seeing them. Moderate winds will be strong enough to drift the fresh, low-density snow into stiff wind slabs in exposed terrain. While these avalanches will be more likely in areas that receive more snow out of this storm, with the increased winds, you're also likely to find reactive wind slabs further west and north in the zone. On Tuesday, skiers in the Icicle Creek area triggered a small wind slab that failed on weak, faceted snow over the EFC. While this avalanche was small, it may be a sign that we could begin to see large or surprising avalanches failing on persistent weak layers with this additional snow load.

    (2/13/2024)

    Skier triggered wind slab on the early February Crust on a NE aspect at 6,500ft in adjacent Stevens Pass on Tuesday.

  • Storm Slabs

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

    You could also trigger smaller, but still consequential, storm slab avalanches in steep terrain sheltered from the wind. With cold temperatures producing high snow-to-water ratios, the favored areas of the East Central could see over 1ft of new snow by the end of the day on Thursday. If you're traveling in these areas and find over 6 inches of fresh snow, keep your travel decisions simple and stick to lower-angle terrain as the best option. Steer around likely trigger points such as steep, convex rolls or gullies even when they exist within lower-angle slopes. 

    While wind slabs will be larger and likely the more sensitive and dangerous avalanche problem, we can't rule out reactive storm slabs in sheltered terrain. New snow will fall on widely variable surfaces, including weak faceted snow, surface hoar, and slick crusts. Adjacent slopes may react quite differently from one another. You can use small test slopes or hand pits to observe the bond with the old snow surface, but these could also give you inconsistent results. It's best just to choose lower-angle slopes until the snowpack has time to adjust to the new snow load.

    (1/8/2023)

    You could trigger storm slab avalanches like in this photo even down in sheltered terrain.

    Photo:

Avalanche Discussion

The brunt of the incoming storm will likely occur overnight, with decreasing snow showers and wind throughout the day on Thursday. Mission Ridge, Blewett Pass, and the Icicle Creek areas could see up to .7" of snow water equivalent, but the cold temperatures will still ring a lot of snow out of those modest numbers. We'll likely end up with 12-14 inches of snow in these favored areas. Further north and west, expect significantly less storm snow totals, but there will still be plenty of wind to drift snow around. 

Two skier-triggered avalanches failed on weak, faceted snow over the EFC over the past few days: a small avalanche in the Icicle Creek area and a slightly larger avalanche on Jim Hill in the Stevens Pass zone. These could be the first signs to expect avalanches on this weak snowpack setup in the future. Observers have been finding buried layers of faceted snow above the stout crust from early February (EFC). On Tuesday, NWAC Forecasters traveled into the Mission Ridge area and found 6-8 inches above the EFC. They also reported reactive wind slabs failing on small surface hoar and facets above the crust. These slabs stayed small (< 1 ft) but were sensitive to triggers due to these weak grains. On Friday, an observer traveled up to 8,000ft in the Stuart Range and found little signs of instability. Other observers also found surface hoar over the early February crust last Tuesday at Blewett Pass. These variable observations and widespread weak surfaces could result in a wide variability of stability after this additional snow load. Consider making conservative decisions during and after this storm until the snowpack adjusts and we have additional information on the distribution of these persistent weak layers. 

You'll generally find 3-5 inches of recent snow over the EFC, with more the higher or further west you go. Expect thin conditions at lower elevations with many hazards, such as open creeks, downed trees, and rough surfaces. 

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