Bulletin d’avalanche

West Slopes South

Northwest Avalanche Center
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Danger d’avalanche

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

More heavy rain will continue to saturate and destabilize the snowpack around the West South zone. Don’t linger on or below large avalanche paths or hanging blocks of snow where you’ll be in harm's way of a wet avalanche. These slides can run far distances and gather significant snow as they descend, growing quite large in the process.

Problèmes avalancheux

  • Wet Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    1.5–2.5

    Rainfall and warm temperatures that have resulted in multiple Wet Slab avalanches in recent days will continue into Tuesday, keeping wet slides on our radar. Water can often linger in the snowpack and produce these unpredictable and difficult to forecast avalanches long after the rain has stopped (which it hasn’t). With conditions like we are experiencing right now, any wet avalanche can entrain significant snow and grow large as it descends. Your best mitigation tool will be to limit the amount of time you spend below large avalanche paths or hanging blocks of snow. 

    While we often only pick one primary wet problem to call out, that doesn’t mean that you won’t encounter others if you venture into the mountains. Wet Loose, Wet Slab, and Glide avalanches are often intermingled. You may see Wet Loose avalanches as a precursor to the larger and more dangerous Wet Slab and Glide avalanches. Throw in sagging and failing cornices, and you have a variety of ways the wet and soggy snow can fail and produce avalanches large enough to bury or kill you.

    (12/24/2022)

    A large natural wet avalanche below treeline in Mt Rainier National Park. 

    Photo: NPS Rainier Rangers

  • Wind Slabs

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

    By the end of the day, temperatures should cool enough that you could find fresh snowfall accompanied by strong to extreme winds at upper elevations. If you find yourself in this more winter-like climate, be on the lookout for freshly building Wind Slabs on leeward slopes or near rocky features. We anticipate any new snow will bond fairly well to the wet and warm surface, but you could run into some trouble in wind-loaded areas. Visibility will likely be difficult, but actively blowing snow or freshly building cornices will key you into the slopes you need to avoid.

Avalanche Discussion

The firehouse that has soaked the West South since 12/23 will continue to spray on Monday night into Tuesday. Water numbers around the zone to this point have been impressive, to say the least. Paradise continues to lead the way with over 5” of water, while areas closer to the crest are hovering close to 3”. Rain, freezing rain, sleet, and the occasional flurry have all been observed during this deluge. It seems like another 1” of water is forecast to impact the zone every 6 hours like clockwork. No matter how much water we actually squeeze out, you should expect continued rain throughout much of the evening Monday night before temperatures start to cool slightly on Tuesday. 

Observations continue to be limited due to the nasty weather, but our professional partners have been able to feed us some useful information. On Monday, Crystal Mountain Pro Patrol reported multiple large to very large slides triggered during their mitigation work. Some of these slides reportedly had crowns 3-5 feet deep and all ran far distances, entraining significant wet snow as they descended. Many of them are suspected to have failed on a weak layer from late November (11/22) that was near the base of the snowpack. In some cases, the slides propagated widely, or adjacent slide paths released sympathetically. While these avalanches were triggered with explosives, it doesn’t mean that similar slides couldn’t occur naturally given the right trigger. Perhaps a falling cornice or large block of snow shedding off a cliff could do the trick. 

Earlier on in the storm, Mt. Rainier Rangers passed along information about some Wet Slabs that had released well below treeline along the road to Paradise. Multiple parties have reported seeing fan-shaped wet avalanche debris over the past few days. On Monday, more wet avalanches and generally soggy snow conditions were reported by the Rainier Rangers. We do not currently have good information about what has happened in other areas of the zone during this rain event. What we do know is that these wet problems will likely linger with us for multiple days until cold temperatures are able to help stabilize the snowpack from the top down.

If you decide to venture through the nasty and wet lower and mid elevations to where the snow is falling on Tuesday, don't underestimate the winds. They should be significant and could create some challenging conditions for both avalanche assessment and travel. Speaking of difficult travel, many obstacles we thought we had buried for the season may have reemerged during this wet period and the creeks may be swollen or blown out. Be prepared for a variety of difficult travel scenarios and to make in-the-field adjustments to your travel plans.

Régions couvertes