Bollettino valanghe

Snoqualmie Pass

Northwest Avalanche Center
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Pericolo valanghe

Tue
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3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
3 · Marcato
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In sintesi

Continued stormy weather and recent avalanches should be enough information to drive you toward simple terrain on Monday. Avalanches should be more likely during periods of intense snowfall or strong winds. Overlapping problems and dynamic weather mean you’ll have to constantly reevaluate your plan throughout the day, so be sure to leave yourself plenty of options for travel.

Problemi valanghivi

  • Storm Slabs

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

    Continued snowfall Sunday night and Monday will increase our storm totals and create the potential for additional weak interfaces. Springtime temperature swings and gusty winds could also create problematic layers within the recent storm snow. To this point, most of the storm snow has been fairly low-density but these environmental factors could change that. Take the time to look at all of the snow over the 4/8 crust to determine if an upside-down snowpack has developed (where heavy snow exists over lighter, weaker snow). In addition to digging, you can use small test slopes to check how the snow is reacting to your weight. Visual clues like cracking of the surface or blocks of snow failing in upslope tests while you travel can help key you into the snow’s slab potential. If you find that slabs exist or the snow is failing easily during your tests, avoid slopes over 35 degrees where triggering an avalanche is more likely.

    (4/10/2022) Widespread D1 storm slabs on convex features failed naturally during a period of high precipitation rates on the morning of 4/10. Photo: Andy Harrington

Avalanche Discussion

Talk about your April showers. Winter-like weather has bombarded the pass since Friday afternoon, delivering over 2 feet of snow above the 4/8 melt-freeze crust to many locations. Observations from upper elevations have been limited due to the ferocity of the storm, but we suspect that over 3 feet of snow exists in many areas, possibly drifted into larger piles. This is the second major storm this week to drop multiple feet of snow on our zone. 

While most of the newly fallen snow has been low-density in nature, it had just enough cohesion to it to produce a widespread natural cycle on Sunday morning. Multiple parties, including NWAC forecasters, reported countless D1 soft slab avalanches on almost every convex slope you could see, even down in the trees. These slabs failed on a density break around 6-8” deep and were easily human-triggered in areas where they didn’t fail naturally. On more planar slopes, Dry Loose avalanches were a concern and will continue to be due to the sheer volume of recent snow. Alpental Pro Patrol reported similar results due to their mitigation work, along with some slabs as deep as 2 feet being released.

On Monday, a change in the storm pattern could result in some different conditions around the zone. First and foremost is a switch in the wind direction toward East. While we’re not anticipating a full east wind event like we often see during the winter, these winds should gust into the moderate to locally strong range. This could easily redeposit the low-density storm snow onto aspects you’re not used to seeing loaded by the wind. In addition, this could create the upside-down snowpack we mentioned above. 

Rising daytime temperatures is another way we could achieve heavy over lighter snow. On Sunday, the surface snow was noticeably heavier midday as temperatures crept up with spring daytime warming. We’re not expecting full sun, but this same phenomenon could present itself on Monday and help the snow “slab up”. It could also kick off some loose avalanches on steeper slopes. With so much recent storm snow, these avalanches could be large enough to be consequential, particularly when a terrain trap is involved. Depending on the amount of warming and solar input, loose avalanches could cross the threshold from dry toward wet fairly quickly.

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