Boletín de aludes

East Slopes North

Northwest Avalanche Center
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Peligro de aludes

Fri
Alta montaña
2 · Moderado
Límite del bosque
2 · Moderado
Bajo el límite
1 · Débil
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Desactualizado: este boletín caducó 4 years ago. Estás viendo condiciones pasadas, no el boletín vigente.

Lo esencial

As you ascend in elevation, keep an eye out for wind-loaded features to avoid. They’ll be more likely on steep convex slopes, near ridgelines, or in rocky areas. You may want to shape your travel plans based on lingering uncertainty about buried weak snow and its ability to produce very large avalanches. 

Problemas de aludes

  • Wind Slabs

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

    The most likely location for you to trigger an avalanche should be in wind-loaded terrain on Thursday. Keep an eye out near ridgelines, confined chutes, or the base of cliffs where wind-drifted snow likes to accumulate. Visual clues such as newly formed cornices or pillow-like piles that look “fat” can help you identify wind-loaded features you’ll want to avoid. 

    (1/17/2023)

    Natural wind slab avalanches near the base of cliffs. 

    Photo: Katie Warren

  • Persistent Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Unlikely
    Tamaño
    1.5–2.5

    You should continue to make travel plans that consider the threat of very large avalanches due to lingering weak layers in the snowpack. While triggering one of these slides is unlikely at this point, you may want to avoid slopes below large start zones where the terrain is more conducive to one of these devastating avalanches. The 1/5 surface hoar layer has frequently been found about 2 feet below the surface and is the primary weak layer on our mind at this point. You’re most likely to find it in wind-sheltered terrain and around areas with sparse trees. Snowpack tests from local professionals have produced harder results, but the structure remains largely intact. If you experience shooting cracks or feel collapses, seek out terrain away from large steep slopes.

    (1/18/2023) A sizeable two tiered crown north of Blue Lake Peak. Overall slab thickness varied from 150cm to 250cm or more. Photo: Willie Webster

Avalanche Discussion

On Wednesday, NWAC observers went to take a look at the very large slide that occurred in Liberty Bowl. While a known failure date is not confirmed, this slide is believed to have occurred between 1/13 and 1/16. Upon investigation, it was determined that the upper crown failed on the Christmas Crust, while the step down was to the mid-November facets (11/22). A crown depth of 5-8 feet was measured. While neither of these is the weak layer we have been talking about in recent days (1/5), this slide helps to highlight the uncertainty surrounding persistent avalanche problems and how they can rear their ugly heads without warning. On Monday, observers at 6,200ft, NW in the Hairpin valley reported sudden and propagating test results on the Jan 5th surface hoar, 2 feet (70cm) below the surface. The results were very hard (beyond the limits of standard tests) and the surface hoar was small and rounding (0.5mm). They also reported moist snow, but no crust in the upper layers. 

Additional observations from Wednesday include avalanche professionals reporting 3-4" of new snow being drifted around by some gusty winds at mid to upper elevations, particularly near ridgelines. On slopes that have seen direct sunshine recently, this snow was sitting atop a thin melt-freeze crust. NWAC observers noted that there was some small surface hoar on top of this crust and near-surface faceting occurring below it. Something to store in the back of your brain for the time being. 

A widespread avalanche cycle occurred late last week and may have been the culprit in the larger Liberty Slide.  It definitely was the culprit for multiple wet avalanches in the lowlands, where we are now left with piles of frozen debris as a reminder and a travel hazard for you to manage.

Regiones cubiertas