Bulletin d’avalanche

Stevens Pass

Dec 16 – 17, 2018Northwest Avalanche Center
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Archivé · expiré 8 years ago

Danger d’avalanche

Tue
Alpin
2 · Modéré
Limite forestière
2 · Modéré
Sous la limite
2 · Modéré
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Points saillants

You can still trigger surprising avalanches at upper elevations. Minimize your exposure to large steep slopes and avalanche paths. If you experience collapsing, cracking in the snow, or see recent avalanches, avoid open slopes 35 degrees or steeper.

Problèmes avalancheux

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    1

    While avalanches have become more difficult to trigger, they could be big enough to bury or kill you. There's uncertainty about these avalanches. Persistent slabs are difficult to predict and often break much larger and wider than you expect. Minimize your exposure to avalanche terrain:

    -Limit the amount of time you spend near slopes 35 degrees and steeper.

    -Put an extra buffer of terrain between where you travel and where avalanches could start.

    -Stay well out from under large avalanche paths and identify safer areas to stop and regroup.

    If you dig in the snow, you will find a layer of sugar-like, faceted snow and feather-like surface hoar buried 3-4 feet below the surface. 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. If you see these warning signs, avoid avalanche terrain.

Discussion

Avalanche Summary

The most dangerous slopes remain at upper elevations where new snow and wind drifting have added to existing slabs. Use extra caution in areas where you see wind drifts, pillows, and variable height of snow. While new snow, strong wind, and rain have all affected the snowpack, the main concern is triggering avalanches due to old, weak layers.  Watch for elevated danger on Tuesday as another storm makes its way into the Cascades.

Snowpack Discussion

Updated Regional Synopsis 20181216

Dangerous and fickle avalanche conditions remain as active weather continues into the week. 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 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. You can find similar snowpack structure responsible for these avalanches in many other locations throughout the Cascades, including Stevens and Snoqualmie Passes. 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 - 12/16: 

  • Mt. Baker: 75”

  • Washington Pass: 35”

  • Stevens Pass: 42”

  • Snoqualmie Pass: 36”

  • Paradise: 51”

  • Crystal Mt Base: 29”

  • Mt. Hood Meadows: 21”

  • Olympics: mix of rain and snow, no net gain

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. Mt. Hood and Hurricane Ridge have low snow coverage below 5000’.

If you're out in the mountains, please let us know what you see.

Be cautious and get home safe.

 

 

 

 

 

 

 

 

 

 

 

 

 

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