Bollettino valanghe

West Slopes Central

Northwest Avalanche Center
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Pericolo valanghe

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

Steep, wind-loaded terrain features and slopes are where you could still trigger an avalanche in wind drifted snow. Avalanche danger could increase throughout the day if the wind begins to transport snow into fresh slabs. 

Problemi valanghivi

  • Wind Slabs

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

    Friday is a between-storm day. The likelihood of triggering an avalanche should be less than the days before and after,  but still possible. Any wind slab from the previous day's storm should have begun to stabilize, but you can still find one. This is especially the case on convex breakovers or other unsupported terrain. Strengthening winds ahead of the next storm will form shallow new slabs, maybe right on top of the old ones. 

    Use all of your tools to track and evaluate wind slabs. The observations you make in the morning could differ from what you need to look for in the afternoon. Cornices and textured snow surfaces can help you find older slabs by identifying the loading pattern during the last storm. Use simple tests - test slopes, hand shears, etc. - to see how well older slabs are gaining strength. Active snow transport later in the day will simply point to where new slabs are forming.

    (12/6/2022) Rime and scoured surfaces helped us anticipate wind loaded slopes. Photo: Dallas Glass

Avalanche Discussion

NWAC forecasters in the Mountian Loop area found near treeline snowpacks ranging from 100-150cm varying on aspect and exposure to wind. There was up to 100cm of new snow from late November over a melt freeze crust.  The structure was right side up with no layers of concern. Testing yielded no significant results and no weak faceted grains were found around this crust. In other zones snowpack observations point towards a slightly weaker structure with facets around various crusts from earlier in the winter. It's worth noting that faceting could still be found east and north in the zone where temperatures tend to be colder.

In West North wind transport was noted in open terrain at and well below ridgelines, and a shallow but dense surface layer produced cracking when tested. Reactivity in new snow and wind slab layers decreased by the end of the day.  One pit near treeline on a south aspect showed 55cm of new snow over the hard suncrust that formed last weekend. No propagation was noted at this interface with testing.

Precipitation totals came to 0.7” low on the west slopes to 0.3” inland. 6" of new snow was recorded near treeline in the mountains east of Darrington. The Baker area picked up the most in the region with 14” while Stevens and Snoqualmie Pass tracked with West Central in terms of precipitation and new snow. While the snowfall has tapered in most areas, convergence zone enhanced snowfall could put down another 4-8” around Highway 20 and the northern Mountain Loop overnight into Friday morning. As you head into the mountains prepare to make your own avalanche, snowpack, and weather observations and factor them into your plan for the day.

 

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