Avalanche forecast

West Slopes North

Northwest Avalanche Center
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Avalanche danger

Sat
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
1 · Low
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Highlights

You can trigger avalanches on steep slopes that collected wind-drifted snow in the latest storm. Avalanche danger could increase throughout the day if building winds begin to transport recent new snow into fresh slabs.  

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–2

    Friday is a between-storm day. The likelihood of triggering an avalanche should be less than the days before and after,  but still possible. Most wind slabs from the previous day's storm should have begun to stabilize, but you can still find one. This is especially the case on convex breakovers or other unsupported terrain. Strengthening winds ahead of the next storm will form shallow new slabs, maybe right on top of the old ones. Be aware that a small wind slab avalanche could step down and trigger a larger avalanche in deeper, weaker layers. 

    Use all of your tools to track and evaluate wind slabs. The observations you make in the morning could differ from what you need to look for in the afternoon. Cornices and textured snow surfaces can help you find older slabs by identifying the loading pattern during the last storm. Use simple tests - test slopes, hand shears, etc. - to see how well the previous slabs are gaining strength. Active snow transport later in the day will simply point to where new slabs are forming. In addition, expect to see some sluffing if you do venture into steeper terrain.

    (12/20/2021)

    Wind affected snow surfaces can help identify areas of wind slab. In this photo the wind was blowing from right to left. In the surrounding area terrain on the right was rocky and wind scoured and terrain on the left was smooth with no texture.

Avalanche Discussion

Observations Thursday trended with “it was snowy and windy in the morning, visibility was not good.” Wind transport was noted in open terrain at and well below ridgelines, and a shallow but dense surface layer produced cracking when tested. Reactivity in new snow and wind slab layers decreased by the end of the day. One pit near treeline on a south aspect showed 1.5' of new snow over the hard suncrust that formed last weekend. No propagation was noted at this interface with testing.

Heather Meadows (favored by the southerly flow of the last storm) received 14” of snow while most other areas around West North picked up 6-10”. While snowfall has tapered in most areas, convergence zone enhanced snowfall could put down another 4-8” around Highway 20, maybe farther north, overnight into Friday morning. As you head into the mountains prepare to make your own avalanche, snowpack, and weather observations and factor them into your plan for the day.

One unusual avalanche from last weekend warrants more attention. It was larger, notably deeper (4’ at the crown), and released above the rider who triggered it. The unsupported start zone averaged 41 degrees and the weak layer was observed as small faceted grains above a hard crust buried on Nov 25th. While definitely an outlier - no other avalanches of this kind have been reported on the west side of the Cascades - it’s still a large, deep avalanche in the middle of a very popular area triggered by a human. It is also a reminder that we have an early-season snowpack built in a period of below average temperatures. Simpler terrain is the easiest way to reduce uncertainty about snowpack.

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