Bulletin d’avalanche

East Slopes North

Northwest Avalanche Center
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Danger d’avalanche

Sun
Alpin
3 · Marqué
Limite forestière
3 · Marqué
Sous la limite
2 · Modéré
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Points saillants

Dangerous avalanche conditions will continue with ongoing wind and light snow. Avalanches may be easy to trigger on steep slopes where you find up to 2 feet of recent snow, and especially where the wind forms drifts below ridges and cliffs. With the potential to trigger dangerous avalanches on older weak layers, it's best to avoid being on or under terrain where very large avalanches could start or run from above.

Problèmes avalancheux

  • Storm Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    1–2

    You're most likely to trigger avalanches in the recent layers of snow near the surface or where the wind has formed deeper, stiff slabs. At lower elevations,  small avalanches in recent storm snow may still be possible on very steep, unsupported slopes. If enough sun gets through the clouds, avalanches could become easy to trigger on southern aspects.

    Expect light accumulation of new snow and enough gusts of southerly wind to transport snow at upper elevations. Take time to test the new snow on inconsequential slopes before traveling in terrain steeper than 35 degrees. Use extra caution near steep start zones at upper elevations and leeward, wind-loaded terrain. Avalanches at upper elevations could easily be big enough to bury you and could involve deeper weak layers.

    (12/20/2021)

    Example storm slab avalanche on a small slope.

    Photo: Adam Butterfield

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    2–3

    A recent load from snow and wind is stressing the underlying weak snowpack structure. If you see cracks shooting through the snow or feel whumphing collapses, stick to slopes under 35 degrees. Put a large buffer of terain between your group and large, start zones and complex avalanche paths above 6,500ft.  Choose smaller, well-supported slopes and stay out from under large overhead terrain.

    Look for strong-over-weak snowpack structure and sudden or propagating snowpack tests results to help you identify the problem. The most problematic slopes will be where you find a thin layer of facets over the Jan 31st crust, 1.5-3 feet below the surface. We have a high degree of uncertainty about how easily you can trigger these avalanches. We know the weak structure exist at most upper elevations. Observers reported very large natural avalanches in the past week, some that are suspected to have run on this weak layer. Observers in the Easct Central zone have triggered multiple persistent slab avalanches. 

    (2/26/2024) Crown line of a very large avalanche visible beneath the cliff band. This avalanche may have run on deeper weak layers. Blue Lake Peak Photo: John Barkhausen

Avalanche Discussion

On Thursday, a group of skiers near Cutthroat Lake (7,100ft, SE) felt a very large collapse and observed cracks that broke several hundred feet across and down the slope. While no avalanche occurred, a quick profile determined a weak layer of facets was 60cm down near the Jan 31st crust. On Silverstar Mountain (north, upper elevation), skiers triggered a large avalanche in recent snow that was 2 feet deep, 75' wide, and big enough to bury a person. Since Wednesday, observers reported a widspread cycle of avalanches, some up to size D3. While many avalanches likely occured within the recent snow from the last week, we suspect some may have ran on older weak layers. Observers reported about 10" of snow since the Wednesday and about 2 feet of recent storm snow since February 25th. We expect another 2-5" of low density snow by the end of Friday.

This week, observers triggered wide-breaking avalanches in wind-loaded terrain at upper elevations. Natural avalanches have been repoted as mostly size D2, with notable larger avalanches in the West Fork of Cedar Creek, the Hairpin Valley, and Blue Lake cirque that may have involved facets over the January 31st crust. The observers near Blue Lake found whumphing collapses and confirmed the instability was on a layer of faceted snow 2ft down above the late January crust.  

Snowpack information is limited outside of the Highway 20 corridor and Harts Pass. Let us know what you find if you get out into the backcountry!

Régions couvertes