Lawinenlagebericht

Stevens Pass

Dec 18 – 19, 2018Northwest Avalanche Center
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Archiviert · abgelaufen 8 years ago

Lawinengefahr

Wed
Hochgebirge
4 · Gross
Waldgrenze
4 · Gross
Unterhalb
3 · Erheblich
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Kernpunkte

UPDATE: High avalanche danger is expected near and above treeline. Heavier amounts of precipitations were received overnight in the Stevens Pass area with more on the way. Very dangerous avalanche conditions are developing in this region.

While you are more likely to trigger an avalanche within the new storm snow, very large, and destructive avalanches can occur and travel to valley bottoms. Stay away from anywhere an avalanche can start, run, or stop.

Lawinenprobleme

  • Persistent Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    2

    Persistent slabs have the potential to wake up during this heavy snowfall and wind loading event, causing very large avalanches. In the past few days, observers have found that the December 9th interface has begun to round, and gain strength. December 13th was the last day that observers reported collapsing on this layer in the zone. This does not mean that we are out of the woods, however. Persistent weak layers are just that, persistent and weak. This next storm will continue to test these deep, weak layers. The snowpack may not speak to you with signs of instability, as they are becoming too far down in the snowpack to be very reactive. The weak interface, though gaining strength, is still there.

  • Storm Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Very Likely
    Größe
    1

    Look for signs of instability like shooting cracks within the new snow, and recent slab avalanches. Any thin, soft storm slab has the potential to step down into deeper weak layers, turning a small soft slab avalanche into a deeper, hard slab.

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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