Bollettino valanghe

Olympics

Northwest Avalanche Center
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Pericolo valanghe

Sun
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
1 · Debole
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In sintesi

Steer around steep slopes near ridgelines where you find wind-stiffened snow.  Soft snow conditions on the northerly half of the compass overlap with the continued low-likelihood/high consequences of triggering a deeper persistent slab avalanche at middle and upper elevations. 

Problemi valanghivi

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–1.5

    SSW ridgeline winds will ramp up on Saturday, redistributing around 2" of new snow, creating shallow, reactive drifts as the day progresses. These slabs may overly weaker snow surfaces (surface hoar or facets) on shaded aspects or crusts on sun-affected slopes. This could make slabs more reactive than you expect in areas where you find a wind skin thickening into a firm, dense layer. You're most likely to trigger these on steep slopes or convex rollovers in the lee of ridgelines. Active transport and fresh, sharp cornices can also help you identify problematic areas, while shooting cracks may give you a warning before you get on a steep slope.

    Example: Rippled, uneven snow surfaces indicate snow was transported by wind.

    Photo: Payton Schiff

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Unlikely
    Dimensione
    2

    Backcountry travelers in the Hurricane Ridge area reported whumpfs on our Persistent Weak Layer (PWL) buried 1–2 feet below the surface last Sunday and Tuesday. A weak snowpack structure remains on northerly aspects, although conditions vary across the terrain. In some areas, the PWL lacks a cohesive slab above it, limiting avalanche potential.  Meanwhile, our neighbors in the Cascades have observed a decrease in persistent slab avalanches over the past two weeks, along with more variable snowpack test results on similar weak layers. This structure has not been stressed recently by a load of snow, but any significant snow or wind loading could increase the slab reactivity, so it is worth paying attention to the overlapping nature of the two problems and use wind slab avoidance to mitigate your risk. Note that areas of the eastern Olympics may pick up more snow, potentially increasing the danger of triggering a weak layer Saturday afternoon.

    If you experience whumpfs or collapses, immediately transition to lower-angle terrain with no overhead hazard. A cornice fall or a smaller avalanche (such as a wind slab) could step down, triggering a deeper, more widespread slide. With the new snow and warming temperatures expected later this weekend, this problem is expected to become more reactive, and demand increased attention. 

    (2/2/2025)

    A widely propagating slab avalanche on a North aspect in the Maggie's area.  A shooting crack on the same slope shot out a whopping 40'.  While this avalanche occurred during a storm cycle, it likely failed on the persistent weak layer we're still tracking. 

    Photo: Anthony Anglikowski

Avalanche Discussion

Very cold, clear weather early in the week has been replaced by seasonably cool temperatures in the 20s from late Wednesday onwards. On Thursday and Friday, NPS Rangers reported that the cold weather had maintained excellent snow conditions on north slopes and due E aspects.  NE winds had built shallow but sensitive wind slabs just below ridgelines, but winds were not tranporting snow on Friday. Despite the cold weather, sunny weather had formed a sun crust on southerly aspects, making for less than pleasant travel conditions.  Surface snow has weekened amidst the cold weather on shaded aspects, with surface hoar remaining anywhere the sun didn't reach. The more concerning layer of weak snow has already been buried:  Facets are sandwiched between a series of crusts (1/10 and 1/29) 1-2' below the snow surface on shaded aspects.  In some areas, there may be a very thin layer of facets above the upper crust.  This crust/facet complex is the likely culprit of a series of widely propagating, human triggered avalanches during the 2/1 - 2/2 weekend and a series of whumpfs last Sun and Tue.   We are going to keep warning about this interface as new snow gradually accumulates and temperatures warm through the holiday weekend.

Share your observations with the community and NWAC. Even if you didn't see an avalanche or a snowpack test, your information is incredibly valuable.  Every afternoon, 4-5 NWAC forecasters from around the region meet to discuss the latest snowpack and avalanche observations, and weather forecast to create the next day's avalanche forecast.  We look at information from the public, other snow professionals, and weather station data to round out our picture.  Share early and often!

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