Bulletin d’avalanche

East Slopes North

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

You can trigger avalanches in the recent snow on a range of steep slopes. Dangerous slab avalanches are a concern at middle and upper elevations. If you see recent avalanches or experience whumpfing collapses and cracks shooting through the snow, stick to slopes under 35 degrees to manage your risk.

Problèmes avalancheux

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    2–2.5

    You can trigger dangerous persistent slab avalanches in specfic terrain. You should be suspect of this anywhere you find snow of 4 Finger hardness or greater over weak, sugar-like facets (or surface hoar). If you see signs of instability, avoid slopes over 35 degrees. Put a large margin between where you travel and any suspect slopes. 

    We have good evidence of the problematic structure from recent observations near Cutthroat Lake, a skier triggered avalanche in Cedar Creek, and a cornice triggered avalanche above the Blue Lake trail. Within the distribution shown above, there are two main snowpack structures of concern: 

    • The recent snow over the January Drought Layer (JDL or 1/31) facets and surface hoar, 1.5-2 feet below the surface. This will be most problematic where the recent snow has gained stiffness, sometimes by wind-drifting.
    • The mid-December facets, (2-3 feet below the surface) are most problematic of the two weak layers. Especially where they're sandwiched between stiff, older drifted slabs.

    (2/2/2025)

    A skier triggered avalanche (D2) that ran on an old weak layer of facets from mid-December. 

    Snagtooth Ridge, NE, 6,600ft

    Photo: Adam Butterfield

  • Loose Dry

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    1–1.5

    The recent snow is dry, cold, and mostly cohesionless. The most likely and more predictable of today's avalanches will be loose. You may see natural avalanches on steep sunny slopes. Manage your terrain appropriately by stopping in safe locations, and don't trigger sluff on top of your backcountry partners. 

    If you travel in terrain that overlaps with persistent slab distribution, you need to manage the risk of that, more dangerous, problem. On those slopes, you won't be able to simply avoid surface instabilities.

    (1/31/2025)

    Skiers easily triggered dry loose avalanches like in this photos over the weekend. 

    Photo: Chris Bartram

Avalanche Discussion

For Friday, expect continued cold temperatures and mostly sunny skies. While winds should be light, watch for subtle drifting. There's lots of light snow that could be easily transported.

A strong storm brought significant precipitation on the 31st-2nd with light accumulation continuing since then. The snow from the past week is very light and totals up to 2 feet. Snow totals vary with exposure to the wind and location east and west in the range. Winds transported snow on the 1st, but have been lighter since then. Observers reported reactive avalanche conditions with the onset of snow on the 31-1st, but then limited signs of avalanchesin the days following . As we near the second weekend in February, the snow has settled and observers ventured further afield. Reports of avalanches and signs of instability are once again increasing.

There's a lot of variability and complexity in layers that formed in the mid and upper snowpack since early December. The simple solution to this uncertainty is to choose more conservative terrain and to avoid slopes suspect for persistent slab avalanches. Consider their potential and consequences at middle and upper elevations, especially where facets formed and were preserved on northerly aspects. You can dig snowpits and use sudden or propagating test to identify the problematic structure.

While the JDL weak layer is present at lower elevations, we don't have evidence showing that it's an issue for triggered persistent slab avalanches. There, the overlying snow lacks cohesion or "slab" characteristics. These areas may become more problematic with future storms or as the recent snow gains cohesion. The deeper layer of facets buried in mid-December has emerged as most problematic for triggering, but it's distribution is even more cryptic and complex. Observations of cracking from Cutthroat Lake on 2/6 and a 2/1 triggered avalanche near Cedar Creek/ Snagtooth Ridge show the mid-December facets being an issue for triggering at middle to upper elevations (approximately 6,500-7,500ft) where they were preserved and layered between harder slabs that were likely stiffened by wind. Additionally, an early January layer of similar structure found in observations from Varden Creek could also be at play. There are slopes within this range where you won't find the facets as they were melted or capped by a crust (high elevation rain event on Dec 7th) or blown away. See more below. 

 On February 2nd, NWAC observers investigated an avalanche near the Snagtooth Ridge that was triggered in an old weak layer up to 3ft deep. (See video and photos below) The avalanche was triggered at 6,600ft on a northeast aspect from a shallow spot in very steep, rocky terrain. The weak layer was into the lower half of the snowpack and was 1-2mm faceted grains. It's believed that these facets were buried on December 17th. On Monday, an NWAC Forecaster found a similar snowpack structure on northerly aspects adjacent to Silver Star Creek. There, the weak layer wasn't problematic for triggering slab avalanches, as the overlying snow was not cohesive. 

You can help us gather more data by submitting an observation HERE or via the Avy App. 

Régions couvertes