Bollettino valanghe

East Slopes North

Northwest Avalanche Center
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Pericolo valanghe

Thu
Alta quota
3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
2 · Moderato
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In sintesi

Shallow storm slabs may become easy to trigger by afternoon, and loose dry avalanches may run fast on steep slopes. The dragons in the basement are the persistent slabs- a weak structure remains in places, and new snow may stress these deeper layers. With the increasing danger comes a rationale to step back, and stick to lower-angled and supported slopes away from large steep faces. 

Problemi valanghivi

  • Storm Slabs

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

    Storm slabs are expected to form during the day on Wednesday as the new snow stacks up. It'll be falling on a range of surfaces with an underlying theme of being weak. As such, the new snow isn't expected to bond well to the old surface. If you find signs of instability like shooting cracks, steer away from steep slopes. For storm slabs, small test slopes can work well, but with such variable old snow surfaces they may not be consistently reliable.

    Loose dry avalanches are expected to run during times of heavier snowfall. Steer clear of larger terrain features if its snowing heavily. 

    Any triggered storm slab could step down to more deeply buried weak layers, become very large, and propagate across terrain features. So increase your margins by sticking to lower-angled slopes and creating a buffer zone between you and potential runout zones. 

    (12/14/2023)

    Large slab below the base of a cliff band in Blue Lake Cirque. The slide likely ran between December December 9th and 10th with light rain that followed about a foot of new snow. SS-N-R2-D2-I

    Photo: Matt Primomo

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    2–2.5

    Persistent slabs may begin to trend towards the 'likely' direction as new snow stacks up. We've been receiving reports of whumphing collapses even as recently as Tuesday, with a few 'sapling shakers' on an ESE aspect at 6,200ft near Varden Creek. Any slide triggered would be surprising, and they can break widely across terrain features. Red flag signs of danger like shooting cracks and whumphing collapses should be heeded, but I wouldn't wait until you get one to avoid steeper slopes. The problematic snowpack structure is in place, and is thought to be more problematic in areas with a shallower snowpack from about Cutthroat drainage and east. 

    Use well supported and lower angled slopes for travel. Stop and regroup in safer areas, well away from and well away from potential runout zones of larger slopes. 

    (1/12/2024)

    Natural avalanches on Tamarack Peak, near Harts Pass. These likely occurred Jan 11th with northwest winds. We don't know exactly which layer these avalanches ran on, but they look suspiciously like persistent slab avalanches. E-SE, 7200ft

    Photo: NCH

Avalanche Discussion

A solid winter storm should give the zone another round of much-needed snowfall. By the end of the day, areas near the crest may have a foot or more of new snow. The storm layer will be landing on a mixed bag of old surfaces, many of which are weaker and likely faceted to some degree. 

Storm totals between January 8th and the 12th were around 2 feet for much of the zone. On the 16th an observer reported 'sapling shaking' collapses on an ESE aspect at 6,200ft near Varden Creek. He dug down and identified the weak layer over 2ft down as soft, sugary grains beneath a crust from Mid-December. On the 12th, an NWAC observer recorded recent wind slab avalanches, one of which may have stepped down to a weaker layer near Goat Peak. Earlier in the week,  multiple parties reported triggering small avalanches in recent storm snow and fresh drifts, and natural avalanches ran with strong northwest winds. Some of these may have stepped down to deeper weak layers, especially near Harts Pass and east. On the 10th, observers reported several large, natural avalanches over 2 feet deep near Cutthroat Lake (NE, ~6,800ft) that may have run on a crust from December 30th. 

You may find up to 6 feet of snow on the ground at upper elevations near Washington Pass, with half that much in the mountains near Mazama. There are several decomposing crusts and layers of sugary facets that developed throughout December. In some locations, these layers present as individual layers; in others, they all meld together. Near and west of the Cascade crest the snowpack is deeper, has less weak layers, and the crusts are typically thicker and more stout.

If you're in the mountains, please let us know what you find.

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