Bollettino valanghe

East Slopes North

Northwest Avalanche Center
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Pericolo valanghe

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

The snowpack has experienced a lot this week and has likely adjusted to the liquid water and heavy snow. The primary avalanche concern is ridgelines at mid- and upper elevations, where the wind drifts fresh snow into shallow, stiff slabs. However, some isolated avalanches in wet snow or older snow layers aren't totally out of the question. 

Problemi valanghivi

  • Wind Slabs

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

    Watch for actively drifting snow, shooting cracks, or stiff snow over softer layers as signs of reactive wind slabs. Ridgelines, confined rocky terrain features, and cross-loaded gullies at upper elevations are the most likely places to encounter this problem. Choose sheltered terrain or steer around steep slopes with deep drifts to avoid triggering avalanches. 

    Warm temperatures and rain well into the upper elevations during the week formed surface crusts, so wind slab avalanches will likely involve just the new snow and stay quite small. But, be particularly cautious in terrain where a small avalanche could cause a fall that carries you over rocks or cliffs. You can evaluate wind slab reactivity by using small test slopes to see if the freshly drifted snow cracks or slides on the old snow surfaces, signs that avalanches are more likely. 

    (1/5/2023)

    An example of a shallow wind slab you could trigger in steep lee terrain below ridgelines at higher elevations.

    Photo: NWAC Public obs

Avalanche Discussion

The snowpack experienced a lot this week, with a major storm bringing 24-48 inches of snow to the region and a widespread natural avalanche cycle. On Friday, temperatures began warming up, and backcountry travelers reported light rain to 7500ft. We expect most wet avalanches to have run their course, but lower elevations could see some additional rain on Sunday, and rock slabs could still release chunks of wet snow. Stick to lower-angle terrain if you're sinking deeply into wet snow, and avoid lingering under cliffs and rocks still holding tenuous blobs of snow. 

Temperatures will cool overnight before snow levels rebound to the 4000ft range as a moderate warm front moves into the region, bringing increasing winds and light rain and snow on Sunday. The main event won't occur until Sunday night when a stronger system will bring more significant snow accumulations to the mid and upper elevations.

Observers in the Delancy Ridge area experienced challenging travel conditions on Saturday due to heavy, wet snow and thin surface crusts. They reported mixed precipitation types and wet snow falling up to 5,000 ft. Stability test results on older melt-freeze layers buried 1-2 feet deep showed moderate signs of instability. We will monitor these as we enter a prolonged stormy pattern through the holiday week. 

Near Blackpine Lake on Thursday, observers reported small avalanches failing on a layer of buried surface hoar. The distribution of this problem is uncertain, and observations indicate that this is not a problem in the Highway 20 corridor or the Hart's Pass area. However, these avalanches are evidence that the eastern portion of the zone may hold a more complex snowpack with avalanche concerns that could linger for an extended period of time. Pay attention to red flag signs of instability, such as whumping collapses, and consider digging down to identify the telltale grey line in the snowpack that clearly distinguishes surface hoar layers. 

You can contribute to the avalanche forecast. Please let us know what you see in the mountains by submitting an observation. 

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