Bollettino valanghe

Stevens Pass

Dec 29 – 30, 2018Northwest Avalanche Center
Vedi sulla mappa
Archiviato · scaduto 8 years ago

Pericolo valanghe

Mon
Alta quota
3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
2 · Moderato
Apri la mappa completa

In sintesi

Continued snowfall will keep the avalanche danger elevated for another day. Evaluate the bond of the new snow carefully. Moderate to strong winds have created deep drifts to avoid near and above treeline.

Problemi valanghivi

  • Storm Slabs

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

    You can trigger avalanches where about a foot of fresh snow accumulates. These avalanches will generally be soft and confined to steep slopes. Moderate to strong winds have created stiffer slabs at upper elevations and in wind-exposed terrain that could break more widely. Use extra caution on slopes over 35 degrees and avoid deeper drifts of snow near and above treeline. Some drifts may get covered up and disguised by fresh snow without wind. Use small, inconsequential test slopes to check and see how the new snow is bonding. A general cooling trend will help these bond, but with continued snowfall this will take time. 

  • Deep Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Unlikely
    Dimensione
    2

    On the eastern edge of the zone, very large avalanches remain possible within an old, faceted layer near the ground. Deep persistent slabs are very difficult to predict. You may not get direct signs of instability with this layer that is likely down from 3 to 5 feet from the surface. What we do know is that after a significant loading event such as this one, deep persistent slabs may become easier to trigger. The snowpack needs time to adjust to the new load.

    Reduce the risk of this low likelihood, high consequence situation by avoiding particular types of steep slopes. Things to look out for are wind stiffened slabs, and where they may overly shallow, rocky areas near and above treeline. Avoid steep, unsupported slopes with recent wind loading. Don’t underestimate how far and wide a slab failing in old snow could run when identifying safer areas to stop and regroup. Be intentional about putting a significant distance in between yourself, and where avalanches start, run, and stop.

Discussion

Snow and Avalanche Discussion:

On the 29th the temperatures warmed up significantly. Temperatures hit 34 degrees at 5200ft on the pass, and a rain crust likely formed up to at least 6,000ft. A widespread cycle of loose wet avalanches were observed, some were large enough to injure, bury, or kill a person. The cold front came in and the precipitation turned back to snow in the evening. Winds were moderate to strong at upper elevations.

Snowpack Discussion

Coming December 30th

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