Bollettino valanghe

Snoqualmie Pass

Northwest Avalanche Center
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Pericolo valanghe

Thu
Alta quota
3 · Marcato
Limite del bosco
2 · Moderato
Sotto il limite
1 · Debole
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In sintesi

As the day goes on, and more snow piles up, expect the avalanche danger to increase especially at upper elevations. Avalanches could occur in areas where the wind drifts the snow into firmer and thicker slabs. Look for blowing snow and textured surfaces to help point out which slopes or features may hold wind-loaded snow that you want to avoid.

Problemi valanghivi

  • Wind Slabs

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

    With the expected modest snow totals and generally cooling trend, the wind should be the key in developing any avalanche hazard. Look for blowing snow along ridges and exposed features to help locate where these wind slabs may develop. Small drifts and textured snow surfaces can also help give you a clue. Wind-drifted snow might be the most obvious near ridgelines, but don’t forget about the sides of exposed gullies and the base of cliffs where you could also trigger one of these avalanches. If you suspect a slope is wind-loaded, steer around and seek out less wind-affected snow.

    (12/14/2021)

    Example: This intentionally skier triggered wind slab occurred on a day with modest snow totals and strong SW winds. Similar conditions are expected Wednesday.

    Photo: Public Observation

Avalanche Discussion

It might take a bit for the avalanche hazard to start to rise on Wednesday morning, but once the snow begins to pile up and the winds start blowing, the danger could rise quickly. We are essentially building a new avalanche problem from scratch. This will happen first at mid and upper elevations where the wind can affect the new snow. At lower elevations and in wind-sheltered areas, the general cooling trend and light snowfall rates should help build a more right-side-up snowpack that bonds well to the previous warm surface. As a result, we don’t expect much more than a few small loose sluffs in these areas. However, this weather forecast is far from a slam dunk. If more snow accumulates than expected or if you experience prolonged periods of heavy snow, look for storm slabs to develop on any steep open slope. At lower elevations, especially west of the Pass, rain on snow could maintain the possibility for small loose wet slides. 

On Tuesday, Snoqualmie Pass experienced a rather strong inversion, and light easterly flow kept the Pass level cold while mid and upper elevations became warm. As a result, the snow surfaces at these upper elevations became wet and heavy. Several natural loose wet avalanches were even seen on steep sunny slopes up to size D1.5-2. This warm surface should help the new snow Tuesday night to stick well to the old interface. As this warm layer cools, it will likely form a new crust that helps delineate storms in the snowpack. 

Below the surface, you may still find several storm layers easy to identify. While we expect avalanche activity to remain in the new snow, one layer to keep on your radar is the snow above and below a crust formed and buried on 12/18. This layer can look a little different depending on elevation but look for a firm or even icy layer about 12-18” below the surface. Several avalanches and significant snowpack test results from this past weekend, highlight the need to keep this layer on our minds. However, given the anticipated new snow loads, we think that avalanche activity will remain above the new/old snow interface. 

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