Bulletin d’avalanche

East Slopes Central

Northwest Avalanche Center
Voir sur la carte

Danger d’avalanche

Sat
Alpin
2 · Modéré
Limite forestière
2 · Modéré
Sous la limite
1 · Faible
Open full map
Périmé — ce bulletin a expiré 2 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

It is possible to trigger an avalanche in wind-deposited snow and unlikely - but not impossible - to trigger a larger avalanche on aspects that harbor a weaker snowpack. Red flags include cracking, collapsing, and recent avalanches. Consider navigating around terrain steeper than 35 degrees where you find pillow-like drifts and cornice development. You can further reduce your risk by choosing short, planar slopes free of hazards and terrain traps.

Problèmes avalancheux

  • Wind Slabs

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

    In the last few days, new snow accompanied by moderate to strong winds built wind slabs in exposed terrain across the zone. Avalanche professionals noted reactivity in wind-loaded terrain on Wednesday and Thursday in the Salmon La Sac, Mission Ridge, and Icicle Creek areas. Expect these slabs to become larger and more widespread as you gain elevation. A warming trend might weaken cornices and cause them to break off and fall more easily.

    Wind slabs usually form just below ridgelines and on exposed convexities and gullies. Visual clues such as cornices, rippled snow surfaces, and dunes will help you identify where the wind has transported snow. Give cornices a wide berth when standing at ridgeline, and don't linger right below them either. Long shooting cracks from your equipment, collapsing, and recent slab avalanche activity are good reasons to choose more sheltered and lower angle terrain.

    Although fairly unlikely, a triggered wind slab could "step down" and become a more treacherous persistent slab avalanche where poor snowpack structure exists. Read below for more details.

    (2/20/2025)

    Morning mitigation at Mission Ridge resulted in wind slabs 1.5-2 ft deep mainly on N-NE aspects.

    Photo: Payton Schiff

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Unlikely
    Taille
    1.5–2

    We haven't seen recent activity on the January Drought Layer (JDL) that brought on a persistent slab problem at the end of January. However, the JDL is still weak and faceted in many areas, so it's worth keeping in the back of the brain. A new weak layer interface that formed around Valentine's Day showed itself to be reactive this week and brought on a new persistent slab problem. After a day or two of warm temperatures, we expect this layer to be well on its way to healing. Areas that have been wind-loaded will be the most likely places to trigger a deeper avalanche on either of these two interfaces.

    You may or may not see clear signs of instability - cracking, collapsing, or recent slab avalanches - telling you to back off before it's too late. Persistent slabs can break in surprising ways, so be cognizant of the terrain around you. Use the clues laid out in the wind slab problem to help you identify wind-loaded slopes, understanding that even a small wind slab avalanche can "step down" and trigger a deadlier persistent slab avalanche. You can reduce your risk by choosing simpler terrain free of consequential runouts. And when in doubt, low-angle it out.

    (2/19/2025) Photo: Payton Schiff

Avalanche Discussion

There is a chance of rain at lower elevations on Friday. If this happens, you may encounter small wet loose avalanches on any aspect. Avoid terrain steeper than 30 degrees until you've found dry snow

The JDL and its overlaying slab are stiffening, making it harder and harder to trigger an avalanche. That being said, one should not forget the abnormal weather circumstances that surround the lore of this layer. Formed over a very long dry spell in January, the JDL is a thick layer, and the facets became well-developed. The contrarily cold weather we saw for a week in February then extended the persistence. This layer has taken longer than we might expect in the PNW to heal, so that's why we're still talking about it!

We now face an atmospheric river event starting on Saturday that could rapidly destabilize the snowpack, especially at these weak layer interfaces. If you plan to get out, it will be vital that you pay attention to the weather and avalanche forecast.

Submit an observation to help NWAC Forecasters reduce uncertainty. It can be short, simple, and even anonymous. Any information you have will help us write more accurate forecasts that will, in turn, better help guide your backcountry decision making.

Régions couvertes