Bollettino valanghe

East Slopes North

Northwest Avalanche Center
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Pericolo valanghe

Sun
Alta quota
2 · Moderato
Limite del bosco
1 · Debole
Sotto il limite
1 · Debole
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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 may be able to trigger small avalanches where you find shallow drifts of new snow at upper elevations. Saturday will bring light snow and relatively calm wind. Expect an increase in avalanche danger on Sunday.

Problemi valanghivi

  • Wind Slabs

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

    Watch for triggering small avalanches in wind-drifted snow on leeward sides of ridges at upper elevations. Steer around drifts and wind-loaded slopes steeper than 35 degrees. You can use a pole to feel for stiffer, wind-transported snow and deeper drifts.  You may find up to 12" of recent snow and drifted slabs up to 1.5 feet deep at upper elevations.

    The initial slabs formed with westerly winds late on Wednesday into Thursday. On Thursday, an observer reported a small wind slab avalanche in Spire Gulley, pictured here. A shift in weather could bring some winds out of the south and east for Saturday. Watch for shallow slabs forming on a new set of leeward slopes. 

    (12/7/2023)

    A shallow crown (20cm) from a small triggered wind slab avalanche in Spire Gulley. NE, 7,300ft

Avalanche Discussion

At the end of the week, 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.

Regioni coperte