Bollettino valanghe

Stevens Pass

Dec 15 – 16, 2018Northwest Avalanche Center
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Archiviato · scaduto 8 years ago

Pericolo valanghe

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

In sintesi

You could still trigger dangerous avalanches at upper elevations. Avoid steep slopes where you see pillows of drifted snow above treeline. If you experience collapsing, cracking in the snow, or see recent avalanches, avoid all open slopes 35 degrees or steeper.

Problemi valanghivi

  • Persistent Slabs

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

    You could still trigger avalanches big enough to bury or kill you. There's uncertainty about how easily you can trigger these avalanches. Persistent slabs are difficult to predict and often break much larger and wider than you expect. The best way to stay safe is to avoid open slopes 35 degrees and steeper where persistent slabs are suspected. Assume that you could trigger a dangerous persistent slab avalanche on any slope where you see wind-sculpted features. Put an extra buffer of terrain between where you travel and anywhere avalanches could start. Stay well out from under large avalanche paths and do not stop near these features.

    You will find a layer of weak, sugar-like, faceted snow down 3-4 feet below the surface of many slopes. Where this snowpack structure exists, you may see signs of instability such as collapsing (a whumpfing sound), recent avalanches, snowpack tests that show propagation, or cracks that travel away from where you impact the snow. These are all indicators that you should avoid avalanche terrain.

Discussion

Avalanche Summary

Overall, the avalanche danger has slowly dropped since midweek. The most dangerous slopes remain above treeline where recent wind has drifted snow over the existing slabs. Use extra caution in areas where you see recently formed pillows, variable height of snow, and wind drifts.

Snowpack Discussion

Regional Synopsis 20181214

We made it through our first strong winter storm and are headed into a weekend with dangerous and fickle avalanche conditions. Thick slabs of new snow (2-5 feet) are perched above a weak layer of faceted crystals. Avalanches triggered on this layer could be very large and life threatening.

Reports continue to come in of very large natural and explosives triggered avalanches in the northern and eastern zones. For perspective, several of these slides have been classified as D3, or large enough to destroy a house.

Anyone accessing alpine areas should limit their exposure to areas where avalanches start, run and stop. In some places the weak snow will talk to you by whumpfing and cracking. In other places, the heavy blanket of new snow is thick enough that it can give a false sense of stability while it masks the dangerous layering below.

Approximate snow totals from 12/10 - 12/14:  

  • Mt. Baker: 55”

  • Washington Pass: 29”

  • Stevens Pass: 37”

  • Snoqualmie Pass: 28”

  • Paradise: 38”

  • Mt. Hood Meadows: 13”

  • Olympics: mostly rain

The change in the snowpack is pretty dramatic with elevation. Height of snow decreases rapidly below 4500’ at Baker and Washington Pass, 5500’ at Crystal/Rainier. The Passes have better low elevation coverage, but it's still pretty thin below 4000’. With additional warm storms in the forecast, this pattern is expected to continue for awhile.

Be cautious and get home safe.

Regioni coperte