Bulletin d’avalanche

Snoqualmie Pass

Northwest Avalanche Center
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Danger d’avalanche

Tue
Alpin
3 · Marqué
Limite forestière
3 · Marqué
Sous la limite
3 · Marqué
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Points saillants

Say goodbye to the sunny and warm weather we experienced over the weekend. Winter returns on Monday as a potent storm brings rain, snow, and wind to the zone resulting in dangerous avalanche conditions. If you see red flag signs of instability such as new avalanches or shooting cracks, avoid slopes over 35 degrees.

Problèmes avalancheux

  • Storm Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    1–2

    The winds are significant with this storm and you will likely start your day managing primarily wind-loaded slopes. Actively blowing snow will be a constant throughout the event, creating thicker and more sensitive slabs on leeward slopes or near rocky features. As the day progresses and storm accumulations increase, the distribution of dangerous slabs is expected to expand to all slopes over 35 degrees. Larger and potentially more reactive slabs will exist as you ascend in elevation or in those wind-loaded areas. Using uptrack tests or small test slopes can help you determine how easily and deeply the new snow is failing. Digging quick hand pits to check the initial bond and locate interstorm layers of concern can further help you identify slab potential. Once 6 inches of new snow has accumulated, your best bet will be to avoid slopes over 35 degrees where triggering an avalanche is more likely.

    (2/7/2023)

    Example of slabs triggered during a storm earlier this week.  Steep terrain, fresh snow, and wind-loading can all combine to create avalanches in new snow layers.

    Photo: Alpental Pro Patrol

Avalanche Discussion

The storm should begin with high-elevation rain on Sunday night before temperatures crash down and allow precipitation to change over to snow by daybreak on Monday. Building in a bit of a buffer just in case the warm temperatures hang around longer than expected - you could encounter a few lingering wet avalanches in the morning hours, particularly at lower elevations. The rain should continue to wipe out any weak surfaces we have around the zone, which were already taking a beating on Sunday in the warm weather and reported period of afternoon drizzle. 

We are anticipating that the new snow should bond fairly well initially to the wet and warm surface. Throughout the day, there will be periods of high precipitation rates, plenty of wind, and a few rounds of convergence are not out of the question. These factors will make triggering an avalanche more likely and help drive increasing hazard throughout the day. You could see a round of small natural avalanches at some point. We do not anticipate cresting the threshold to very dangerous avalanche conditions (High), but if you find that the snow is piling up and large natural avalanches are occurring, dial your terrain selection way back.

On Sunday, NWAC forecasters as well as other avalanche professionals in the zone took a look at the upper snowpack above the 2/3 interface. While some layers were highlighted during small column tests, none showed much interest in propagating and no new avalanches were reported. We anticipate you will be dealing with primarily new snow problems on Monday but wouldn't be surprised to hear of a deeper release in isolated locations.

In the neighboring Steven's Pass zone, two separate avalanches have been reported on deeper layers in the past two days, one of which spanned a large alpine bowl. We have not seen any similar activity in the Snoqualmie Pass zone, but you may want to check out the Stevens Forecast for more information and keep it in the back of your mind.

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