Bulletin d’avalanche

West Slopes South

Northwest Avalanche Center
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Danger d’avalanche

Sun
Alpin
3 · Marqué
Limite forestière
3 · Marqué
Sous la limite
2 · Modéré
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Périmé — ce bulletin a expiré 4 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

Saturday should be the finale of the rainy weather that has resulted in dangerous avalanche conditions around the zone. It can take a while for water to drain out of the snowpack, so give it the time it needs to heal by avoiding slopes over 35 degrees. After a storm like this, there’s always a lack of information, so be sure you make flexible travel plans and are prepared to make your own observations.

Problèmes avalancheux

  • Wet Slabs

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

    Even as the atmospheric river wraps up on Saturday, recent rain that has soaked our snowpack up to around 7000 feet will still need some time to drain. Wet avalanches are not well understood and difficult to forecast, but they can occur long after the rain has stopped. These unpredictable slides are difficult to manage, so your best tool will be to avoid slopes over 35 degrees on Saturday where an avalanche can start, run, or stop. This includes being aware of the terrain above you such as sagging cornices, blocks of snow on rock ledges, or larger avalanche paths. 

    Wet avalanches could come in a variety of forms on Saturday, including Wet Loose avalanches starting from a point and fanning out as they descend, pockets of Wet Slabs, or larger Glides and Cornices. They could even be intermingled with loose slides triggering slabs for example. Regardless of what avalanche problem you encounter, your management of them will generally be the same. Put these slides on your radar anywhere you encounter wet and soggy snow.

    (1/12/2023)

    A widely breaking natural slab avalanche was observed in the backcountry near Crystal Mountain on 1/12. Additional slabs and loose avalanches were observed in similar terrain.

    Photo: Eddie Schoen

Avalanche Discussion

The West South has been hit fairly hard by this most recent atmospheric river event, with NWAC weather stations at Crystal Mountain and Paradise outpacing other areas of the zone. As of Friday afternoon, these stations are sitting around 2.5” of water since Wednesday evening and we anticipate to be close to 3” by the time Saturday dawns. This event started out as snow in many areas but quickly transitioned to rain as freezing levels shot up to around 7000 feet. Even though we’re not quite finished with the rain, the end is in sight for this event.

On Saturday, precipitation is expected to start to taper and temperatures should slowly cool to a more moderate 5000-foot freezing level. As this process unfolds, winds should start to ramp up across the zone, impacting areas closer to the crest and maybe even a few flakes will fall from the sky at upper elevations. While snow totals are expected to be minimal, if you find yourself in the alpine where snow is falling and the wind is blowing, keep an eye out in case some small Wind Slabs form. If you’re high on a volcano, expect drastically different conditions and potentially multiple feet of new snow.

Observations over the past few days have obviously been limited by the rain and undesirable weather. A public observation from the Crystal Mountain area relayed there were multiple slab and loose avalanches from earlier on in the cycle. The picture submitted along with the observation shows a widely breaking slab. While we only have a picture to go on, it looks as if this slab may have broken on the buried surface hoar identified by NWAC forecasters prior to the storm at the 1/4 interface. Multiple layers of interest were found in the nearly 3 feet of snow over the Christmas Crust prior to the rain, and we suspect that at least some of them may have failed during this event. 

The general cooling trend and increasing winds should help the snowpack to start to stabilize from the top down, creating a new crust in the process. Once formed, this crust will be just one of the multiple surfaces you may encounter as you venture back into the mountains. Wet punchy snow, breakable crust, firm crust, swollen creeks, exposed natural hazards, and refrozen avalanche debris could all present different hazards as you travel.

Due to the general lack of good information from throughout the zone, we’re headed into this holiday weekend with a bit more uncertainty than we typically like. If you’re out and about, we’d love it if you’d send us some pictures of the snow or avalanches wherever you’re recreating.

Régions couvertes