Bulletin d’avalanche

Snoqualmie Pass

Northwest Avalanche Center
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Danger d’avalanche

Mon
Alpin
3 · Marqué
Limite forestière
3 · Marqué
Sous la limite
2 · Modéré
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Points saillants

A dynamic storm will bring snow, rain, wind, and fluctuating freezing levels to Snoqualmie Pass midday on Sunday. As precipitation starts to fall and winds increase, you will know that it's time to start dialing back your terrain selection and being suspicious of steeper slopes.

Problèmes avalancheux

  • Wind Slabs

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

    Increasing winds throughout the day will transport newly fallen snow into Wind Slabs. These slabs are often formed on leeward slopes near ridgelines, the side of gullies, or the base of cliffs. Apart from these locations, steep slopes over 35 degrees and convex rollovers may be the most likely spots for you to trigger a slab on Sunday. With such strong winds, actively blowing snow should be your first indicator of Wind Slab development and their location. You can also look for freshly building cornices or if you have visibility, textured snow surfaces to help you identify potential areas of danger. Use test slopes, hand pits, and uptrack tests in non-consequential terrain to help you identify how the new snow has bonded to the previous surfaces and if a slab exists. If you notice a poor bond or cracking in the new snow as you travel, avoid slopes over 35 degrees, particularly ones you suspect are wind-loaded.

    (3/20/2021) Using visual clues is a great way to help identify the potential for Wind Slabs.

  • Loose Wet

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

    We may see some rain at the start of this event at lower elevations, possibly triggering some natural Wet Loose avalanches. The warm and sunny weather the past few days softened snow surfaces on aspects that see direct sunshine and resulted in Wet Loose avalanches throughout the zone. This may limit any potential Wet Loose cycle due to rain, but not fully eliminate it. These avalanches could be more likely on slopes that have not seen direct sunshine lately and are still harboring colder, drier snow, particularly as you reach middle elevations. These avalanches could entrain significant snow and run far distances as they descend. If rain is starting to fall, take note of your location in terrain and head toward lower angled slopes, keeping away from any overhead hazard.

    If we receive a significant amount of rain, an additional overhead hazard to avoid are the numerous glide cracks in our zone. These avalanches are unpredictable, so be sure to give slopes with glide cracks a wide berth by not traveling underneath them.

    (12/18/2020) Soggy conditions at the start of the storm could produce some Wet Loose avalanches like this one at lower elevations.

Avalanche Discussion

This storm is forecasted to pack a bit more of a punch than our normal springtime storm. The predicted wind speeds of 40-55 mph by day’s end really jump out to us, and the rate at which it approaches the region is another atypical characteristic. Although it approaches quickly, we shouldn’t see stormy weather impact the zone until the afternoon hours. So you may not see the avalanche hazard we are predicting if you decide to make an early morning trip to the mountains. If the forecast holds, 8-10” of new snow should accumulate at middle to upper elevations with plenty of wind, resulting in dangerous avalanche conditions in the afternoon. At lower elevations, fluctuating freezing levels may result in rain and a wet avalanche cycle before changing to snow and putting dry avalanches on your radar. 

We anticipate a mix of snow surfaces for the new storm snow to fall on, including firm crusts, moist snow, and packed powder. Be sure to evaluate the bonding of new snow carefully, it could vary greatly depending on what prior snow surface is present. Additionally, cornice development will be aided by the strong winds associated with this storm. Look for current cornices to thicken and fresh cornices to develop on leeward ridgelines. Cornices are susceptible to human triggers and notoriously break back further than expected, so give them a wide berth by not traveling on them and minimizing time spent below them. 

During the ongoing Covid-19 pandemic, continue to follow the latest guidance from local, state, and federal health officials. Avoid unnecessary risks that could impact first responders and stress medical resources.  Wear a mask when appropriate, practice social distancing, and consider recreating closer to home.

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