Boletín de aludes

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Northwest Avalanche Center
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Peligro de aludes

Sun
Alta montaña
2 · Moderado
Límite del bosque
2 · Moderado
Bajo el límite
1 · Débil
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Desactualizado: este boletín caducó 2 years ago. Estás viendo condiciones pasadas, no el boletín vigente.

Lo esencial

Winds formed stiff slabs where you could trigger an avalanche on most aspects. However, these avalanches could be larger where slabs rest over weak snow layers on northerly aspects. Steer around steep slopes below ridgelines, the base of cliffs, and steep rollovers in the terrain where you find firm, textured drifts. 

Problemas de aludes

  • Persistent Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Possible
    Tamaño
    2

    Winds have stiffened snow surfaces throughout the terrain, and it may now be easier to trigger large persistent slab avalanches on northerly aspects. Use extra caution in steep rocky terrain where the snowpack is shallow and variable.  Signs of instability, like avalanches, whumpfing collapses, or shooting cracks, are bullseye signs to avoid steep slopes and keep more significant safety margins between you and large avalanche paths. Over the last few days, there have been multiple reports of wind slab avalanches on the weak, faceted snow of the January Drought Layer (JDL). Most of these have been small (D1-1.5), but since the slabs are quite hard, they could be more likely to break above you and carry you through the terrain below. 

    You can find facets from the January Drought Layer 1-2ft below the snow surface. The reactivity and distribution are still uncertain, but consider avoiding slopes over 35 degrees, where you find stiffer snow over surgery, weak facets. Facets from early January and December, buried 2-3 feet deep under old stiff wind slabs, are more isolated. While these layers are less likely to be problematic, consider the consequences of triggering a much deeper avalanche. 

    (2/7/2025)

    A natural avalanche that likely ran on the 4-5th. The wide propagation suggests that it could have ran on the January Drought Layer. 

    Photo: Katie Warren

  • Wind Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Possible
    Tamaño
    1–1.5

    The recent strong winds formed widespread wind slabs throughout mid and upper-elevation terrain. On northerly aspects, these formed over the weak January Draught Layer and could be larger with wide propagation. On more southern aspects, these likely formed over thin sun crusts. Cracks shooting through the snow and recent avalanches are signs you should stick to lower-angle terrain. Identify stiff, wind-textured drifts and steer around them in steep terrain.

    Cornices have grown larger with the recent winds. Avoid getting too close to these hazards, and don't linger underneath them. A large cornice fall could trigger a wind slab on the slope below. 

    (2/9/2025)

    A small skier-triggered wind slab in the Cutthroat Drainage caught and carried a skier without injuries. 

    SE, 7100ft, SS-AS-R1-D1

Avalanche Discussion

It doesn't seem like this storm will pack much moisture for the northeast Cascades but expect light snowfall to increase throughout the day on Saturday. By the end of the weekend, we could see 4-8 inches of snow in the Washington Pass Area. Temperatures will moderate back to more seasonal norms in the mid-20°s. 

On Friday, NWAC Observers in the Twisp River area noted increasing westerly winds and significant blowing snow along ridgelines. The snowpack in this area of the zone was shallow and faceted, but where they traveled at mid and lower elevations, the lack of an overlaying slab limited avalanche concerns. On February 13th, observers reported a large (size D2) natural avalanche resulting from a cornice fall. They also reported a skier-triggered hard wind slab avalanche. Both were at upper elevations on northerly aspects and may have involved the January Drought Layer. On Feb. 9th, an observer triggered a small wind slab on a crust and was caught and carried on a southeast aspect. Over the last 3 days, multiple human-triggered and natural wind slabs have been reported. While most of these avalanches have been relatively small, one was reported to have surprisingly wide propagation, indicative of a persistent slab. As backcountry users venture out into more remote areas of the zone, there are also growing reports of large and very large avalanches that occurred during the storm at the beginning of February. We suspect these avalanches failed on the weak, faceted January Drought Layer (JDL). 

NWAC forecasters, observers, and other professionals in the Highway 20, Washington Pass area have found substantial evidence of weak snowpack structure throughout the zone. The early February storm brought 1-2 feet of snow to the zone that fell on either the JDL persistent weak layer or wind-stiffened snow over the JDL. The JDL exists at lower elevations. However, it doesn't seem to be a current issue for triggering persistent slab avalanches since the overlying snow lacks cohesion or "slab" characteristics in many places. 

Less likely, but still a concern, are deeper layers of facets buried by older wind-drifted slabs during mid-December through mid-January. The distribution of this layering is more cryptic and complex but has been observed between 6,500-7,500ft in moderately wind-exposed terrain. An avalanche triggered on 2/1 near Cedar Creek/ Snagtooth Ridge is an example of where the mid-December facets were problematic. There are also slopes 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. 

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

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