Bollettino valanghe

Snoqualmie Pass

Northwest Avalanche Center
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Pericolo valanghe

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

You could see some shallow Wind Slabs develop above the rain/snow line as an incoming storm washes over Snoqualmie Pass. At lower elevations, rain on snow might result in some wet avalanches for you to dodge. Limit your time spent under slopes that contain large cracks that look like a brown frown.

Problemi valanghivi

  • Wind Slabs

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

    We’re expecting just enough snow and wind at mid to upper elevations that you could encounter some shallow Wind Slabs on lee slopes on Monday. Look for actively blowing snow or fresh drifts that look “fat” in comparison to the surrounding terrain to help identify wind-loaded features to avoid. They’ll be more likely near ridgelines and rocky terrain or on convex rollovers.

    (3/17/2023)

    Snow sifted to the base of cliffs by light easterly winds on 3/17. Look for Wind Slabs on specific terrain features such as this on Monday.

    Photo: Andy Harrington

  • Loose Wet

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

    At lower elevations, expect new precipitation to come in the form of rain. Although most aspects may have gone through a Wet Loose cycle over the weekend due to solar input, protected areas such as shaded northerly aspects are still holding drier snow. These slopes could be the most likely to destabilize once rain on snow occurs. That doesn’t mean you won’t find wet avalanches elsewhere, however. If you’re standing in the rain and see the signs of wet avalanches such as new rollerballs or fan-shaped avalanche debris, head for lower-angled slopes.

    Other types of wet avalanches could occur at lower elevations which are harder to manage and forecast. After a weekend of warm and mostly sunny weather, adding liquid precipitation to the snowpack will further our concern for unpredictable Glide avalanches. If you notice large crevasse-like cracks on a slope, be sure to give it a wide berth.

    (3/13/2023)

    Example: These rollerballs occurred due to rain on snow at lower elevations a week ago. You might see similar activity on Monday, particulary on northerly aspects.

    Photo: Shane Robinson

Avalanche Discussion

As stated above, it was a generally warm and sunny weekend around Snoqualmie Pass with temperatures reaching the 40s and even 50s at some automated weather stations. This resulted in fairly widespread Wet Loose avalanche activity on most aspects except true northerlies. As temperatures cool with our incoming storm wave, expect these warm and wet surfaces to lock up and become a new crust. On those shaded aspects, there is well-settled powder with, in places, weak surface hoar. On Monday, you should dig with your hand to take a look at how well the new snow has bonded to the underlying surface. 

We suspect the majority of avalanche activity to involve the new storm snow, which could run far and fast on the underlying crust if it is poorly bonded. If overlaying the surface hoar on northerly aspects, slides could break widely or even wrap terrain features. Outlier events would be the isolated Glide avalanches mentioned above or a chance for a slightly deeper Wind Slab pocket at upper elevations on shaded slopes. The chances of these are pretty slim, however. 

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