Avalanche forecast

Stevens Pass

Dec 22 – 23, 2018Northwest Avalanche Center
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Avalanche danger

Mon
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
3 · Considerable
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Highlights

Significant new snow and strong winds are building dangerous avalanche conditions. Expect avalanche danger to rise through the day on Sunday. Use caution on all slopes over 35 degrees and avoid wind drifted features near and above treeline.

Avalanche problems

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1

    Over a foot of fresh snow could accumulate by Sunday afternoon forming fresh storm slabs. The most dangerous slopes are at upper elevations where avalanches could be large. Stay off of steep slopes near and above treeline where the wind has drifted thick slabs. You can trigger avalanches on any slope 35 degrees and steeper where the new snow is poorly bonded. If you choose to travel in avalanche terrain, carefully evaluate the new snow.

    Recent avalanches are the best indicator that you should avoid avalanche terrain. Use small, inconsequential slopes and tests to check if the storm snow will slide. A variety of old surfaces, from soft snow to crust, have created variable bond between the storm snow and older layers.

  • Deep Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely
    Size
    2

    You could trigger Deep Persistent Slabs in the eastern portion of the zone and on steep, shaded slopes facing west through north through east. While these avalanches are generally difficult to trigger, they are also hard to predict. If you initiate an avalanche in the storm snow in wrong spot, it could result in a very large and dangerous avalanche.

    The best way to reduce the risk of this is a low likelihood, high consequence scenario is to minimize your exposure to terrain capable of producing large avalanches:

    -Limit the amount of time you spend on or 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.

Snowpack Discussion

Regional Synopsis: December 19, 2018

Why has the avalanche danger been so high for so long? Two reasons: A very active and wet weather pattern combined with a widespread persistent weak layer.

For perspective, the approximate snow totals from 12/9-12/19 are:

  • Mt Baker: 102”

  • Washington Pass: 55”

  • Stevens Pass: 76” mid-mountain

  • Snoqualmie Pass: 68” mid-mountain

  • Crystal Mountain 70” Green Valley

  • Paradise: 78”

  • Mt Hood Meadows: 44” mid-mountain

  • Olympics: 48”

In many areas, a layer of buried surface hoar and/or weak sugary facets was buried on December 9th. This layer has been the cause of numerous natural, explosive, and skier triggered avalanches. As this layer gets deeper it gets harder to assess. In short, the scenario is tricky and getting more dangerous by the day.

Higher snowfall totals along the Hwy 542 corridor/Mt Baker area have driven several avalanche cycles during this period. Loading from recent storms has been more incremental to the east and south of the Mt. Baker area, so we have not yet experienced a widespread cycle in other areas.

When will we reach the breaking point? It’s hard to say. What we do know is we have a deep weak layer, reports of very large explosives triggered slides at Mission Ridge and Crystal Mountain, and more storms on the way.

Be patient and continue to stick to lower angle slopes with nothing above you.  This is a good time to avoid areas where avalanches can start, run, and stop.

We’d like to thank all of you who have sent NWAC your observations. If you are out in the mountains, let us know what you see.

Regions covered