Bollettino valanghe

East Slopes North

Northwest Avalanche Center
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Pericolo valanghe

Tue
Alta quota
3 · Marcato
Limite del bosco
2 · Moderato
Sotto il limite
2 · Moderato
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Non aggiornato — questo bollettino è scaduto 3 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

You could still trigger avalanches due to the recent snow and steady winds. Upper elevations in wind-affected terrain are the likeliest places for large avalanches. Avoid steep terrain below ridges and the base of cliffs with pillow-like drifts. 

Problemi valanghivi

  • Wind Slabs

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

    The heaviest precipitation ended early on Sunday, but sustained winds likely drifted this snow into wind slabs where you could trigger avalanches. Slopes below ridges, the base of cliffs, and steep gully walls are likely places to find wind slabs. Cracks shooting through the snow, actively blowing snow, and recent avalanches are indicators of the danger. You can use quick tests on small slopes to test the reactivity of the wind slabs and recent snow. There are also likely lingering storm slabs out there. While these avalanches would probably be smaller, they could still have high consequences if you are pushed into obstacles or caused to fall in very steep terrain. 

    (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

  • Loose Wet

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

    Temperatures are forecasted to cool slightly, but we probably aren't putting the snowpack into a solid freeze. So, you might trigger some small wet loose avalanches in lower elevations in steeper terrain. Even though the sun is not very strong this time of the year, it may become the tipping point with the addition of mild temperatures. Even smaller wet avalanches might be strong enough to knock you over or push you into trees and rocks. Be aware of the instability, and consider moving to lower-angle slopes if you're sinking deeply into wet, heavy snow. 

    (12/10/2023)

    Natural wet loose avalanche near Hart's Pass.

Avalanche Discussion

The East North lucked out to stay below freezing during the bulk of the precipitation over the weekend. But the warm air is still making its way into the Methow Valley, along with some sunshine for the afternoon. The storm dropped just under 1ft of new snow with steady winds. Many folks enjoying the fresh snow reported natural avalanches throughout the zone, from Harts Pass to the Hairpin. While the likelihood of triggering a slide is decreasing, it's also always a good idea to step into new terrain slowly. Don't commit to larger slopes before first seeing how the snow reacts on many small, lower-consequence slopes. 

Prior to the weekend, observers assessed the snowpack. Near Washington Pass, professionals found snow depths of ~2.5 feet below 5,000ft. Higher up, they reported up to 4 feet of snow on the ground, including new snow totals (since 12/6) of up to 1 foot at upper elevations.  On Thursday, Willie Webster traveled throughout the Highway 20 corridor.  The entire snowpack at the aptly named Rainy Pass had been wetted all the way to the ground. Any weak layers that had existed there are likely no longer an issue. In the Hairpin Valley, Willie found less impacts from rain including the November 30th surface hoar intact and producing propagating test results and whumphing collapses. This was likely an isolated instability that subsided as the 12/6 Hanukkah crust froze and gained strength.

The November 30th surface hoar may still be intact in cold valley bottoms east of Washington Pass. Even in these areas, you can find the weak layer in the middle of the snowpack, capped with a layer of 6-10" of melt forms that add strength to the snowpack. I suspect that even where the surface hoar is found, it likely is no longer a culprit weak layer for avalanches.

From November 30th through December 6th, the weather station at Washington Pass recorded nearly 5" of water equivalent, with the last 2" falling as rain from December 4-6th. Rain levels may have spiked around 8,500ft on the 5th while heavy rain fell. Observers reported a widespread cycle of wet avalanches up to size D2.5, along with dry slab avalanches that occurred prior to the warm-up. Observations and access to the mountains during this time were limited.

If you got out, please let us know what you found in the mountains by submitting an observation.

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