Bollettino valanghe

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Northwest Avalanche Center
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Pericolo valanghe

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2 · Moderato
Limite del bosco
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In sintesi

Warming temperatures and increased sunshine will destabilize previously dry snow. Plan your tours to accommodate the solar clock, pivoting to cooler, shadier, and lower angle aspects as rollerball activity starts up. In steep, wind-loaded, or rocky start zones you can still trigger a stubborn wind slab that can harm you.

Problemi valanghivi

  • Loose Wet

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

    We think that there's more snow to be impacted mostly sunny skies warming temperatures on Friday. Snow shedding off rocks, trees, and cliffs will produce rollerballs and small natural avalanches. Avalanches will be more likely to hurt you where the wind has drifted the snow more than 6" deep or in steep, rocky terrain where even a small avalanche may be traumatic. As soon as you observe signs of rollerball activity, expect wet loose avalanches to follow.  Transition to cooler, shaded aspects. If the 2/24 crust melts, you could see avalanches entrain slightly more deeply, but we think this likelihood will be low. On northerly aspects, lower elevation slopes may warm enough that you can trigger an avalanche in consolidating, moistening snow. If you find this occurring, dial back your slope angle.

    Example: (3/12/2021) Small, natural Wet Loose avalanches and rollerballs.

  • Wind Slabs

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

    Westerly winds have loaded E-SE aspects. Focus your attention toward where fresh, sharp cornices are overhanging lee slopes and steer around these steep avalanche start zones. Slabs 6" or deeper where you can trigger a wind slab will be found primarily at upper elevations and near ridge crest locations. 

    Example: (3/20/2021) This Wind Slab was intentionally triggered by a cornice drop on Saturday in the Crystal Backcountry. One of the deeper slides found by NWAC forecasters, it released 8-10" deep. [NW 6300'; SS-ASc-D1-R1-S]

Avalanche Discussion

Observers in the Maggies area of Hurricane Ridge found 1-2 inches of new snow that fell Wednesday night through Thursday. The new snow sits above a rain crust formed up to 5500 ft (3/24). Around 6" of additional snow sits above a crust on 3/21 melt-freeze crust on W-S-E aspects.  On S slopes, these two crusts are around 2 inches apart and on N-NE if the 3/21 crust exists there can be 6+ inches of snow between the crusts. The layer between the crusts has a poor density profile forming a slab layer that had modest reactivity on a NE aspect at 5100 ft. Slab avalanches will be unlikely to occur on this layer as it should be on a healing trend. The observers also found a minor wet loose cycle that began around 1 PM on Thursday. 

No new avalanches were reported at Hurricane Ridge last weekend. Observers on Sunday noted loose, dry snow on northerly aspects and variable conditions with a mix of surface crusts on other aspects in the Hurricane Ridge area.  On Saturday, NPS rangers reported whumpfing and shooting cracks on low-angle North aspects near treeline.  The interface was likely the 3/18 pre-storm layer. We don't have any signs of recent reactivity on this layer.  About 2 ft of snow accumulated at Hurricane Ridge during a period of S-SW winds Thursday through Sunday that drifted recent storm snow onto W-N-E aspects.

Cornices have grown large in recent week. They have a nasty habbit of breaking further back than travelers expect. Cornices can also fall and trigger a wind slab or wet loose avalanche on the slopes below. Minimize time on the slopes below them.

During the ongoing Covid-19 pandemic, continue to follow the latest guidance from local, state, and federal health officials. Avoid unnecessary risks that could impact first responders and stress medical resources.  Wear a mask when appropriate, practice social distancing, and consider recreating closer to home.

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