Bulletin d’avalanche

Stevens Pass

Northwest Avalanche Center
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Danger d’avalanche

Fri
Alpin
3 · Marqué
Limite forestière
3 · Marqué
Sous la limite
2 · Modéré
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Points saillants

Update 0700: Sensitive soft slab conditions should be expected.

A burst of new snow, cooler temperatures, and increasing winds are creating dangerous conditions. Look for blowing snow, shooting cracks and fresh avalanches. You could trigger an avalanche at all elevations as the new snow piles up, so stay off of steep or unsupported slopes if you find instabilities.

Problèmes avalancheux

  • Wind Slabs

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

    Stay on alert for signs of wind slab such as blowing snow, fresh drifts, and shooting cracks in freshly deposited snow. Increasing wind speeds during the day may quickly create wind slab hazard. You are most likely to run into this problem near and above treeline in exposed locations, such as the leeward sides of ridges and near rocky outcrops. Avalanches could also be larger at upper elevations, where there is more snow and drifts are deeper.

    Steer around convex rolls and pillowed snow on steep slopes. Stay off of steep slopes altogether if you find evidence of instability such as shooting cracks. 

     

    (12/19/2021)

    A crown from an avalanche (size D2.5) that ran on 12/18 in storm snow. Similar wind slab avalanches could occur on  Wednesday. Above treeline, NW, Chiwaukum range

    Photo: Matt Primomo

  • Storm Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    1–1.5

    Another round of snowfall is expected overnight into Thursday. Storm slabs could develop within the upper layers as accumulations begin to stack up. You may be most likely to trigger a small, soft slab on very steep and unsupported features, such as convex rollers. Use test slopes to evaluate how the new snow is bonding as the day progresses. Loose avalanches or sluffs may be worth considering in steeper terrain and during times of heavy snowfall.

    (12/20/2021)

    Example small storm slab, near Highway 20 in the East North zone.

    Photo: Adam Butterfield

Avalanche Discussion

The pass picked up 5-8" of new snow fell on Wednesday, and more is on the way. Expect another round of similar amounts of snowfall into Thursday, but the temperatures should cool off markedly. Winds should pick up as the day progresses, leading to increased hazard in high, exposed areas. There is some potential for a Puget Sound Convergence Zone to swing down into the area in the afternoon. If it does, expect stormier conditions, and increased avalanche danger.

On Wednesday, SPMR reported triggering some small (2"-5") storm slabs first thing in the morning. Other observers noted deep, heavy snow near and below treeline. The new snow has initially bonded well as temperatures were warm as the snow fell. 

The snowpack is generally strong and getting deeper. Observers have noted that it has settled out noticeably over the past few days. A number of crusts may be found in the snowpack, although they aren't expected to be problematic for avalanches. A thin melt-freeze crust was buried late on the 21st and could be found not too far beneath the snow surface. A pair of crusts from late November/early December can now be found 4-5 feet below the surface.

Régions couvertes