Bulletin d’avalanche

West Slopes North

Northwest Avalanche Center
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Danger d’avalanche

Sun
Alpin
3 · Marqué
Limite forestière
3 · Marqué
Sous la limite
3 · Marqué
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Points saillants

Human and naturally triggered avalanches are likely at all aspects and elevations, especially during periods of intense snowfall and strong winds. The threat of very large natural avalanches running down into mid or lower elevations is reason enough to minimize your exposure to large avalanche paths overhead. 

Problèmes avalancheux

  • Storm Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    1–2

    Another round of heavy snowfall will begin early Saturday with 1” of snow or more per hour expected with cold front passage mid-morning. Strong winds will accompany the storm and make for deeper slabs in wind loaded terrain. The rapidly accumulating load of new and/or wind drifted snow will simply overload the upper snowpack before it has time to adjust. 

    Between avalanche danger and stormy conditions, it will be a good day to start with a  conservative mindset in lower angle, wind-sheltered terrain. Monitor changes in snow depth as you gain elevation or change aspects. Use simple observations like test slopes in safe areas or hand shears to see how the new snow layers are bonding and how this changes throughout the day. While wind loaded areas should be easy enough to identify, all steep slopes will be suspect during periods of intense snowfall, sun breaks, or other weather factors that cause conditions to rapidly change. 

    Example of typical, shallow storm slabs in wind sheltered terrain. Expect to see deeper slabs in wind loaded areas  Saturday

    Photo: Simon Trautman

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    3

    Three very large (D3) avalanches were reported on Wednesday. They likely released on a layer of weak facets buried on March 8th. They remain a concern not only in alpine terrain where they initiated but also at lower elevations where they deposited large debris piles. There is a chance you could trigger one on Saturday but for most of us weather conditions will limit travel above treeline. The more likely scenario is that one occurs naturally in terrain above and descends into runout areas at lower elevations. Uncertainty about this avalanche problem runs high - we may see anywhere from zero to many of these slides in surrounding terrain once the storm clears. Plan your day to avoid being in harm’s way - avoid being under big, alpine avalanche paths during and immediately after Saturday’s storm.

    (3/16/2022)

    Very large debris piles from avalanches on the Shuksan Arm. Notice the people standing on the debris. These avalanches were triggered with control work and ran about 1500' vertical feet down into treeline.

    Photo: Jason Matkowski

Avalanche Discussion

Reported avalanche activity on Friday was limited to instability from warming with slow-moving wet avalanches in the new snow, pinwheels, etc. Given the time of year expect to see some form of wet loose activity most days when there is some combination of new snow and strong sun, rain, greenhousing, or a simple rise in temperature.

The pattern of recent avalanche activity combined with the coming storm is tricky. Smaller new snow and wind slab avalanches are common with storms of this size and intensity. Instability with these avalanche types will probably follow the typical Coastal snowpack curve - danger will be quick to rise as the storm builds and probably quick to fall afterward.

A greater concern is the faceted layer above the early March rain crust. It is present throughout the Cascades in some form or another but has only spurred avalanche activity in distant zones. In the West North, we have avalanches that likely occurred in this layer but observations from relevant terrain are scarce. We just know something a bit weird is out there when there are very large avalanches with unusual characteristics or in unusual locations. We do know all reported avalanches were on northwest to east aspects at upper elevations. Though the same faceted layer can be found at lower elevations, the grains appear to be gaining strength and large snowpack tests have not produced significant results. However small column tests have continued to fail suddenly in some instances. Combined with the coming storm, we are left with a big question mark - will more load trigger more big avalanches? With this level of uncertainty there are really only two options-  stay out of the way and see what happens in the coming days or be in the way and be OK with greater risk that you can’t really evaluate in a meaningful way.

 

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