Bollettino valanghe

West Slopes South

Northwest Avalanche Center
Vedi sulla mappa

Pericolo valanghe

Sat
Alta quota
3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
2 · Moderato
Open full map
Non aggiornato — questo bollettino è scaduto 6 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

Complex, overlapping, and potentially dangerous avalanche problems on some unusual aspects should cause you to pause and choose simpler terrain. Steer around large open slopes, especially when you notice drifts behind objects or suspect the wind loaded snow onto a feature. With additional snow, any avalanche could grow large and destructive.

Problemi valanghivi

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    1–2

    You may find new wind slabs in some unusual locations Friday. Easterly winds likely formed fresh drifts on any exposed slope or feature. Unfortunately, a few inches of additional snow could hide the most obvious signs of wind loading. Instead, you’ll want to watch for subtle drifts and changes in how the snow feels to anticipate which slopes may harbor slabs. If you suspect the wind loaded a slope, go around. Seek out lower angled or less wind affected terrain. Some of these slabs may sit on top of very low density or weak surface snow allowing them to trigger easily and break widely. Since you may find it easy to trigger slabs in some unusual locations, approach this common problem with a bit more caution. 

    (2/9/2021) This widely breaking slab was observed at Paradise on Monday (2/9). [6500' E aspect. Photo: Porter Michaels]

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    2–3

    Plenty of uncertainty surrounds our persistent avalanche problem in the West South. We know the snowpack structure still exists. Professionals over the past few days observed the same weak facets over the mid-January crusts. These layers continued to fail in snowpack tests. However, no new avalanches have occurred since last weekend’s storm. What does that mean? We may be entering a classic low-likelihood/high-consequence scenario. If you trigger this persistent layer, it could propagate widely and produce a large and deadly slide. Let the potential consequences rather than the likelihood of trigger guide your terrain choices. You’re most likely to cause a persistent slab avalanche on large open start zones at mid-elevations.

    (2/6/2021) Multiple slabs were observed on an E aspect at 6300' in the Crystal backcountry on Saturday (2/6). Deeper slides are suspected to have run on the Mid-January crust/facet combo while shallower Wind Slabs were also observed. [Photo: Jeremy Allyn]

Avalanche Discussion

While this series of storms don’t seem too impressive, the very cold temperatures could turn these modest precipitation amounts into quite a bit of light fluffy snow. In wind-sheltered areas, you may trigger loose avalanches that run quickly. While sluffs are often small and relatively harmless they could act as the trigger for deeper avalanches in large terrain. 

We believe the weak snowpack structure continues to linger in all the areas of the West South. Nothing in the recent weather nor snowpack observations suggest that this layer has gained significant strength. If you dig in the snow you may find a layer of sugary facets just above the prominent and stout mid-January crust. This layer should sit 3-5’ below the surface. While snow profiles and snowpack tests can highlight this weak layer they are not a decision making tool. This structure very closely resembles snowpacks just north of the zone in the Snoqualmie, Stevens, and East Central zones responsible for several avalanche involvements and one fatality. (See the short video in the media gallery below for more information). You can help us track this weak layer by submitting snowpack observations on our public site.

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.

Regioni coperte