Bollettino valanghe

East Slopes Central

Northwest Avalanche Center
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Fri
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In sintesi

You could trigger large wind slabs on upper elevation, exposed terrain on Thursday. Loose wet avalanches may be easily triggered, and run on steep slopes that face the sun. The potential size of avalanches will increase as you gain elevation and move closer to the Cascade crest, where more recent snow has fallen.

Problemi valanghivi

  • Wind Slabs

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

    Strong westerly winds have been transporting the new snow onto lee slopes. Winds may have created slabs further downslope or below ridgelines. The potential size of wind slabs will increase as you gain elevation, and near the Cascade crest where more recent snow has fallen. Look for signs of instability such as shooting cracks, and stiffer textured snow over weaker snow. Feel for textured wind-affected snow as you change aspect and elevation. For the most part, avalanche activity should be confined to new snow, but avalanches could step down to recent storm layers and weak snow over a crust around 2ft deep above treeline.

    Give cornices plenty of room when traveling on ridges and stay out from under them. Cornices could be touchy to triggering and they could trigger slab avalanches below.  Travelers are surprised every season when cornices break further back than they expect. 

    (3/22/2021) Small wind slab release on a test slope. Notice the rippled texture to the snow surface.

  • Loose Wet

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

    Warming temperatures and sunshine will initiate a round of loose wet avalanches on very steep slopes facing the sun. Look for signs of loose wet activity such as rollerballs, and other small fan-shaped avalanches as the daytime warms up. The potential size of loose wet slides will increase where you find more than 8" of new snow, such as areas in the Salmon la Sac. Here, they could grow to become large. Don't let these predictable avalanches catch you by surprise in or around terrain traps or extreme terrain.

    Loose dry avalanches are possible on very steep slopes in the shade. Ride cautiously in steeper terrain knowing that you could initiate sluffs that may entrain loose snow and grow larger.

    Example loose wet avalanches from Snoqualmie Pass on 3/23.

Avalanche Discussion

As is typical for the East Central zone, snowfall totals vary widely from Wednesdays storm. New snowfall amounts taper off for areas to the north and east within the zone. 0.8" of water equivalent fell at Fishlake Snotel in the upper Cle Elum drainage, 0.3" at Lyman Lake/Trinity, with around an inch of snow at Mission Ridge. Strong westerly ridgeline winds blew through the day with gusts into the 60's at Mission Ridge. The new snow fell on a mix of suncrusts on east to south to west aspects, and cold dry snow surfaces on northerly aspects. Surface hoar and small near surface facets were observed in neighboring Stevens Pass zone prior to the snowfall, so the recent storm snow could be sitting on these weak surfaces in some areas. On Monday, I went out to Van Epps Pass area, and found around 8" of new snow. We stayed off of steep slopes that appeared thickly wind-loaded near ridgelines. The more recent storm likely added to the potential size of any wind slabs in this area.

A crust and adjacent weak layer formed in mid-January can still be found about 2-6 feet below the surface throughout most of the zone.  Several different avalanche cycles released down to this interface, with the last cycle producing avalanches up to size D4.  Avalanches down to this layer are now unlikely with the last known avalanche down to the mid-Jan crust/facet combo recorded on March 1st.  We're watching the upcoming weather pattern for major warm-ups or storm events to see when and if these deeper layers will be tested again. The most suspect areas for deep persistent slabs are shallow, rocky, and unsupported slopes, especially where overhead cornice fall could trigger avalanches.

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