Boletín de aludes

East Slopes Central

Northwest Avalanche Center
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Peligro de aludes

Tue
Alta montaña
3 · Notable
Límite del bosque
2 · Moderado
Bajo el límite
2 · Moderado
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Desactualizado: este boletín caducó 5 years ago. Estás viendo condiciones pasadas, no el boletín vigente.

Lo esencial

Warming temperatures will add uncertainty to an already complex snowpack. Significant, and destructive deep slab avalanches have released naturally, and ski triggered wind slabs have occurred on a layer of buried surface hoar. Continue to make conservative terrain choices and avoid going on, or underneath steep, wind loaded slopes while the snowpack settles.

Problemas de aludes

  • Deep Persistent Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Possible
    Tamaño
    3

    The uncertainty and unpredictability of deep persistent slab avalanches should determine where and how you travel as temperatures rise to the warmest they have been in well over a month. Avoid going in or underneath steep slopes, especially recently wind-loaded areas above 4,500ft. Cornices are big in some areas, avoid going underneath these because if they break they could create very large avalanches. East to south to west aspects are the most concerning and have recently produced avalanches over 1,500ft wide. Slabs could be over 8 feet deep near the crest, and around 3ft deep further east in the range.

    A persistent weak layer involving facets on or sandwiched within crusts that were buried in mid-January has plagued the snowpack with lingering instability for over a month. They have been documented on all aspects, and above 5,000ft. Unfortunately, this problem isn't going away, and we shouldn't be surprised to hear about more of these dragons in the coming days. Continue to tread carefully around places where these could release while the snowpack adjusts.

    (2/27/2021) This avalanche ran sometime between Friday and Saturday morning. East aspect at around 5,400ft (estimated) in Icicle Creek.

  • Wind Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Possible
    Tamaño
    2

    Wind slabs could remain reactive to human triggering on Monday. Wind slabs have been recently triggered on a layer of buried surface hoar between 1ft and 2ft+ deep near Blewett Pass, and in Icicle Creek. Avalanches may also be triggered outside of wind affected areas in the deeper storm snow near the crest. A sun crust from the middle of the week was responsible for a close call with a skier triggered avalanche in the adjacent Stevens Pass zone. If you trigger an avalanche in the upper foot or two of snow, it could be large or even step down to become a very deep and destructive avalanche. With wind slabs, storm slabs, and the potential for deep slab avalanches, you should avoid large avalanche paths, especially at mid and upper elevations. Avoid recently wind-loaded, leeward slopes 35 degrees and steeper.  Stick to lower angled and well supported slopes and features.

    Example wind slab.

  • Loose Wet

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Possible
    Tamaño
    1–2

    The warm temperatures may create wet loose avalanches on all aspects below treeline on Monday. If the sun is out where you are, expect these to happen on steep slopes that face toward the sun most readily. Moist, sticky snow and rollerballs are good indicators that the snow is capable of producing these. Get off of steep slopes at lower elevations by mid-afternoon to avoid this problem.

    Example small wet loose avalanche.

Avalanche Discussion

We're in for a fairly significant warm-up on Monday. This adds uncertainty to a snowpack still settling with lots of recent storm snow. Stay observant, and keep your eyes peeled for signs of instability. Here is an elaboration on a couple of the problematic layers in the snowpack of the zone:

Upper snowpack: Ski triggered (D1.5 and D2) avalanches occurred on north and east aspects in Icicle Creek at 5,400ft on Saturday. These were over 2ft deep x 200ft wide, and observed to have run on a layer of recently buried surface hoar. On Friday at Blewett Pass observers found a couple of layers of buried surface hoar stacked within wind slabs, 1ft and 2ft down, respectively. These were on both shaded and south facing aspects at about 5,800ft and produced clean, planer shears. A recent natural slab spotted on Saturday ran on a southeast aspect at around 5,600ft near Doctor Creek and looked about 1.5ft deep x 80ft wide.

Deeper down: Much deeper, recent natural avalanches appeared to run Friday or Saturday on the mid-January layer in the terrain in Icicle Creek (see photo below) and in the Chiwawa. A deep persistent slab occurred on the 24th near Manastash Ridge, and appeared to have slid on our mid-January crust. Snowpack tests on Friday near Blewett Pass showed that people can still trigger avalanches on this layer there as well.  

From the 20-23rd a massive storm brought up to 6" of water equivalent to the mountains near the crest, but much less to the Wenatchee Range further east. Numerous avalanches (Many D3-3.5's, some size D4's)  ran on, or around the 22nd in the mountains near the crest, and some deeper slabs were reported from the Wenatchee Range. See the photo gallery below.

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