Bollettino valanghe

Snoqualmie Pass

Northwest Avalanche Center
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Pericolo valanghe

Sat
Alta quota
3 · Marcato
Limite del bosco
2 · Moderato
Sotto il limite
1 · Debole
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Non aggiornato — questo bollettino è scaduto 3 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

Expect the avalanche danger to increase as you ascend Friday. More snow and strong winds at mid and upper elevations will form new slabs that may trigger easily. Blowing snow and sharp cornices can help you identify wind-loaded areas you want to avoid.

Problemi valanghivi

  • Wind Slabs

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

    Fresh wind slabs will form along exposed ridges, near the base of cliffs, and in the tops of chutes as this storm continues to impact the Snoqualmie area. Expect slabs to grow in size and distribution as you gain elevation and as the day continues. So, if you start to see signs of wind-drifted snow, assume it will only get worse as you head higher and as the day progresses. Look for clues like blowing snow, drifts, textured surfaces, and new cornices to help you anticipate wind-loaded terrain. 

    Prior to this storm snow surfaces varied by aspect. Firm crusts were found on E-S-W slopes, while faceted weak snow was seen on the more shaded side of the dial. This means some of these new wind slabs fail easily and run quickly. As they grow larger in the afternoon, these attributes could make them quite dangerous. 

    (2/18/2023)

    Signs of wind loading to look for Saturday.

    Photo: Dallas Glass

Avalanche Discussion

A return to winter has brought snowfall back to the Pass. As of Thursday afternoon, storm totals vary significantly with elevations. At ~3000ft only a trace of new snow has accumulated. Near the top of Alpental (5470ft), closer to 6-7 inches has fallen. The storm will continue overnight and into Friday with lowering snow levels. 

As the storm turns more showery and convective in nature mid-day, you could experience a few brief moments of sunshine. If this happens, don’t be surprised when you see rollerballs and small loose wet slides release from steep sunny slopes. By the afternoon a more intense band of showers (convergence zone) could take aim at the Pass. This would create locally stormy conditions with heavy snowfall rates that may quickly increase the danger. 

Even though temperatures are cooling and snow is returning, avalanches like glide slabs won’t stop on a dime. The recent warm and sunny weather sent water deep into the snowpack and it will take a bit for it to drain or freeze. Continue to steer clear of areas below crevasse-like cracks. 

Since we’re starting from scratch below treeline, it should take a bit for enough new snow to accumulate to present a hazard. The snow should bond well to the warm and wet surface. By Friday afternoon, you could start to see a few isolated wind slabs in exposed areas of the below treeline band. 

Prior to the storm, warm, often sunny, weather radically affected the snowpack. A crust formed on E-S-W aspects high into the terrain, and on more shaded slopes at lower elevations. In higher northerly areas, dry soft snow persisted through our little taste of spring. However, if other zones are any indication, it could have begun to facet and grow weaker. Below this old surface, we don’t have any significant layers of concern. As a result, we expect avalanche activity to generally stay near or above the 3/22 interface.

Regioni coperte