Bollettino valanghe

East Slopes North

Northwest Avalanche Center
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Pericolo valanghe

Sat
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
2 · Moderato
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In sintesi

You could trigger very large avalanches on deeply buried weak layers, especially at middle and upper elevations. Look for simpler, less steep, and more supported terrain while this dangerous problem lingers. You can also trigger small avalanches due to fresh drifting from southerly winds at upper elevations

Problemi valanghivi

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    2–2.5

    Put a larger buffer of terrain between your group and large start zones or complex avalanche paths above 6,500ft. Choose smaller, well-supported slopes and stay well out from under larger features. Signs of instability can be inconsistent, creating a tricky problem that is essentially 'unmanageable'. You might not receive signs of instability before the whole slope fails. It could be the 2nd, 3rd, or 8th person on the slope that triggers it. A layer of surface hoar and facets were buried on 2/24, as was faceted snow over a strong crust from late January. You could find these layers 2-4ft down respectively. There's copious evidence of these layers being the culprits of numerous very large natural avalanches and close calls in the zone. 

    (3/5/2024)

    A very large avalanche was remotely triggered by skiers on 3/2 on Kangaroo Ridge. The crown was ~70-100cm deep, and it ran on a layer of facets (1.0mm) buried in mid-February, just above the 1/31 crust.

    Kangaroo Ridge, Pk 8183, WNW, 7,600ft

    Photo: John Stimberis

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–1.5

    Southwesterly winds have been just strong enough to drift low-density snow into thin slabs. On Friday, winds will shift southeast and increase in the afternoon. Though shallow, these slabs could be fairly reactive as they'll have formed over faceted surfaces. Look for signs of wind slabs, such as blowing snow or textured surfaces. You may encounter shooting cracks. Identify terrain and features within it where these are likely to exist. Although the consequences of one of these slabs may be minimal, any shallow slab could step down and trigger a much larger avalanche on deeper weak layers. 

    Wind drifting snow near ridgelines.

    Photo: Matt Primomo

Avalanche Discussion

Friday should be another beautiful day in the mountains, with a bit more cloud cover than the past few days. The strengthening March sun has warmed snow surfaces, especially on steep SE-SW aspects. Observers reported loose avalanches (wet and dry) on steep, sun-exposed slopes this week. You may see a few more small loose wet slides on Friday. On Tuesday, skiers at upper elevation slopes triggered a few small wind slab avalanches.

On Tuesday, forecasters visited the site of a remotely triggered (D3) avalanche on Kangaroo Ridge. They found that the avalanche was ~2.5-3 feet deep and ran on a layer of facets buried in mid-February, just above the Jan 31st crust. Many tests still produced sudden or propagating results indicating that backcountry travelers could still trigger similar avalanches, especially in areas of relatively shallow snowpack. Multiple close calls, natural avalanches, and snowpack observations in the Highway 20 corridor point to a few weak layers buried in the month of February in the top 2-4 feet of the snowpack. Another close call occurred last weekend on the southeast nose of Cutthroat Peak (6,400ft, SE); a party remotely triggered avalanches that propagated to either side of them, a total of 800-1000ft. Widespread, very large natural avalanches occurred between February 28th and March 1st.

Snowpack information is limited outside of the Highway 20 corridor and Harts Pass. Let us know what you find if you get out into the backcountry!

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