Lawinenlagebericht

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Northwest Avalanche Center
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Lawinengefahr

Tue
Hochgebirge
3 · Erheblich
Waldgrenze
2 · Mässig
Unterhalb
1 · Gering
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Kernpunkte

You can trigger a wind slab that may step down to a weaker layer 1-2 or deeper in wind-loaded areas. The likelihood of triggering a slab is gradually increasing, but the consequences of a potentially widely breaking avalanche remain. Steer around steep wind-loaded slopes, particularly at upper elevations and on shaded aspects near ridgelines.

 

Lawinenprobleme

  • Wind Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Likely
    Größe
    1–2

    A 2" snowstorm produced drifts up to 4 ft or more in the Hurricane Ridge parking lot by Sunday morning thanks to strong winds Saturday through Saturday night. A rider was caught and carried in a small hard slab with a 12" crown on  the north side of the Maggies Ridgeline on Saturday. ONP rangers also triggered a small wind slab at 4800 ft on an E aspect on Sunday. Slabs may rest over a weaker 2/13 interface in some areas. We're expecting variability with potentially more reactive slabs in areas where the winds kept the snow surface colder on Sunday, such as near ridgelines and at upper elevations. Continue to navigate around steep, wind-loaded slopes with the awareness that a thicker slab would be difficult to escape. Slabs could be firm, widely breaking and might be hard to recognize under an inch of more fluffy snow. 

    Example: Blowing snow and firm pillow-like drifts are great clues to anticipate wind load slopes. 

    Photo: ONP Rangers

  • Persistent Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    2

    A persistent slab needs both a slab and a weak layer. We've had that weak layer since the start of February and it wakes up with each round of snow and wind loading. The most recent event peaked Saturday and Saturday night with reactivity gradually decreasing through the long weekend. The way to avoid this problem is by keeping a larger buffer between yourself and the steep wind-loaded areas that now have a slab. In some areas, warming snow on Sunday could consolidate into a slab. If the snow feels slabby and cohesive for any reason, investigate the crust/facet layers from January further before exposing yourself to terrain of consequence on the northern half of the compass. Whumpfs or collapses confirm the problem and warrant avoidance of all open slopes steeper than 30 degrees. We suspect that collapses in the Royal Basin area on Saturday were a sign that the weak layer could have produced an avalanche on a steeper slope. A cornice fall or wind slab could step down, triggering a deeper, more widespread slide. 

    (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

We're expecting 1-2" of snow through Monday with light winds and relatively steady temperatures. Very shallow new slabs could form, but we're primarily dealing with slabs formed over the weekend and our PWL.

In areas out of the wind at middle and lower elevations, greenhousing on Sunday warmed the upper snowpack at Steeple Rock. The crust-facet sandwhich in this location was shallower in this location, only down 8-12", and this warming seemed to impact the facets, making them stick together (a sign of healing). The warming has also decreased the riding quality on shaded aspects in many areas. The tricky thing is that the warming doesn't appear to be the case everywhere. At Hurricane Ridge proper the snow stayed much colder thanks to a light but consistent breeze. We expect that in many areas near ridgelines and at upper elevations, the snow stayed cold, helping preserve the potentially reactive wind and persistent slabs on shaded aspects.

The greenhousing in wind-sheltered areas also caused rollerballing on shaded aspects. At lower elevations, warming was pronounced and produced small wet loose avalanches: The Tunnel ran to the Park road (size 1), but there wasn't a lot of snow to entrain at this elevation. Similar temperatures will remain at lower elevations on Sunday, so you may be able to form slab or wet loose avalanche in moist or sticky snow on a steep slope. Rollerballs and small natural wet loose avalanches are also a possibility on the southern half of the compass if the sun comes out.

Here are some details about the PWL we are tracking:  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.   At lower elevations, we don't think there's yet enough snow loading to create a problem.

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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