Lawinenlagebericht

Snoqualmie Pass

Northwest Avalanche Center
Auf der Karte ansehen

Lawinengefahr

Tue
Hochgebirge
3 · Erheblich
Waldgrenze
2 · Mässig
Unterhalb
2 · Mässig
Open full map
Veraltet — dieser Lagebericht ist 5 years ago abgelaufen. Du siehst vergangene Verhältnisse, nicht den aktuellen Bericht.

Kernpunkte

A return to snow on Monday could continue to stress weak layers created over the weekend or create a new point of failure for avalanches. Avalanches will be more likely on upper elevation slopes over 35 degrees, but don’t ignore convex features, the base of cliffs, or unsupported slopes no matter what elevation you’re at. 

Lawinenprobleme

  • Storm Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Likely
    Größe
    1–2

    Storms Slabs were reactive over the weekend at all elevations. With the return of some snow on Monday, slabs could thicken and continue to be reactive, especially as you ascend in elevation or in wind-loaded terrain. Take special care on convex features steeper than 35 degrees, near the base of cliffs, or on unsupported slopes where avalanches are easier to trigger. There are now multiple storm interfaces for you to investigate as potential points of failure in the upper snowpack. Using test slopes can key you into slab potential and how the upper snowpack is reacting to your weight. Hand pits, while you travel, are an easy way to look for heavy snow over lighter snow (upside-down) or the depth of layers of concern. If you find an upside-down snowpack, suspect a slope to be wind-loaded, or notice blocks of snow failing during your tests, avoid slopes over 35 degrees.

    (12/19/2021)

    This is one of multiple slab avalanches in the Alpental Valley that released naturally on 12/18 or the morning of 12/19 and is believed to have failed at the base of the recent storm snow (12/18 interface).  This slope is unsupported and convex.

    Photo: Kurt Hicks

Avalanche Discussion

Sunday was a bit of a break between storms in the Snoqualmie Pass zone, but we should get right back into the snow business on Monday. This past weekend produced a widespread avalanche cycle with both natural and human-triggered avalanches up to size D2 reported. Most of these avalanches appeared to have failed at the base of the recent storm snow (12/18 interface) approximately a foot below the surface at lower and mid-elevations. Snowpack tests performed by various professionals yielded sudden results and propagation in extended column tests, helping to confirm our concerns for this layer. 

A variety of precipitation types fell on Saturday throughout the zone, meaning the slab above the 12/18 interface may look a little different depending on your location. At the pass proper, you will find some rimed precipitation particles and graupel, along with an ice crust about 6” below the surface. The crust is reported to be semi-supportable and Alpental Pro Patrol was able to trigger avalanches below the crust and down to the 12/18 interface during their mitigation efforts on Sunday. Keep both of these interfaces in mind on Monday along with the bonding between any new snow and the current snow surface. Although these instabilities could be on the mend, they may still be capable of producing avalanches.

Further West in the zone, more rain than frozen precipitation fell on Saturday where elevations are lower and the East Flow was unable to keep temperatures as cool. Slush slides were reported to have occurred up the Middle Fork Road, and natural hazards such as open creeks, punchy snow, and shallowly covered rocks and stumps are common. Regardless of your location in the zone, look out for these hazards at lower elevations as we continue to build our early season snowpack

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