Bollettino valanghe

Stevens Pass

Northwest Avalanche Center
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3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
2 · Moderato
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In sintesi

Yet another stormy day will maintain dangerous avalanche conditions above 5000ft. You could easily trigger avalanches on slopes greater than 35°, and they will be larger on steep slopes with deep wind drifts. Choose low-angle terrain and avoid steep convex rolls and wind-loaded slopes.

Problemi valanghivi

  • Storm Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    1–2

    Frequent storms with fluctuating temperatures have created a layered and complex snowpack with various interfaces where avalanches may fail. Choose conservative terrain and pay close attention to red flag signs of instability, such as recent avalanches, cracking, or collapsing. Avoid steep, unsupported or open slopes and convex terrain features, all likely places to trigger an avalanche. You could also trigger larger, more dangerous wind slab avalanches on lee slopes below ridgelines. Identify wind-affected snow using cornice formations, hollow-sounding drifts, or textured surfaces. Choose slopes below 30° in wind-loaded terrain or travel on wind-ward or scoured surfaces. 

    Use small features and quick tests to see how easily the snow slides before moving onto larger slopes. While it's less likely, there's a chance that you could trigger much deeper avalanches on a layer from the beginning of the week. Dig down about 2-3 feet and use snowpack tests to locate this layer, just above a crust. 

    Temperatures will cool slightly on Sunday, but at lower elevations, you could still trigger small, loose wet avalanches. Watch for rollerballs in moist snow to indicate that you could trigger a slide. You can avoid these avalanches by staying above the elevation of moist snow or sticking to lower-angle slopes. 

    A skier triggered an avalanche (D1.5) from outside the Stevens Pass Ski Area earlier this week. NE, 5,400ft.

    Photo: Adam Butterfield

Avalanche Discussion

This next storm won't pack quite the punch of Saturday's, but we could see a few inches of snow at slightly cooler temperatures by the end of Sunday. On Saturday, many observers reported triggering small avalanches within the new storm snow. The avalanches were mainly small, 6-8 inches deep, and failed on the recent interface (12/28).

A big takeaway from this ongoing storm saga is that the frequent snow, rain, and fluctuating temperatures have limited the distribution of our observations and prevented the snowpack from adjusting before the next storm rolls through. This leaves us with significant uncertainty at upper elevations and a layered, variable snowpack at mid- and lower elevations. 

While most storm instabilities appear to resolve after a couple of days, a weak layer buried on the 22nds is one to watch. You can find it 2-3 feet below the surface, and just above the thick Solstice Crust. This layer was the culprit in a few larger avalanches triggered by Stevens Pass patrol on the 26th and backcountry skiers on the 24th on Rooster Comb and Lake Susan Jane outside the Stevens Pass Ski area. I was in the Henry Creek area on Saturday (12/28), and this layer still produced unstable test results at 4100ft. While the interface consists primarily of decomposing stellars (snowflakes) some profiles have revealed small faceted grains.

At elevations below 3800ft, the snowpack is saturated, and the surface is littered with rain runnels. Above this, the snowpack is moist instead of wet, and 2-5 feet of snow rests over the Solstice Crust, depending on your elevation and proximity to the Crest. At 4100ft in the Henry Creek Drainage, I found 2.5 feet of snow over the Solstice Crust and an average snowpack height of 5 feet. The Friday warmup created a new melt-freeze crust below Saturday's new snow, 4-5 inches in this location. 

If you're in the mountains, let us know what you see by submitting an observation.

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