Bollettino valanghe

Mt Hood

Northwest Avalanche Center
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Pericolo valanghe

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

Firm and dangerously slick crusts warrant the sharps and know-how to self-arrest as we transition back to winter.  Actively drifting snow will help you identify fresh pockets of slab near ridgelines that may be hazardous above a terrain trap or long, steep slope. If you encounter a poor refreeze at lower elevations, stick to slopes less than 35 degrees.

Problemi valanghivi

  • Wind Slabs

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

    We're expecting several inches of fresh snow to arrive with moderate winds Wednesday night into Thursday. Uncertainty with this problem largely depends on how much snow and whether the wind speeds are optimal for slab formation. The problem will be minor and fairly easy to avoid. Identify the areas of snow stripped to the crust and note areas where winds have redistributed that snow into the lee of terrain features. 2" of snowfall can produce isolated 6" slabs large enough to knock you off your feet in steep terrain. Slabs will shear easily on and are unlikely to bond well to the newly formed crust. Cracking snow surfaces can help you identify this reactivity before you move into wind-loaded terrain. Steer around these oblong patches of snow accumulation along the upper lee walls of a canyon where the slope angle exceeds 35 degrees. If we end up with more snow, the more of these landmines will be more extensive and could push into the middle elevations. You're most likely to get into trouble where a slide knocks you off your feet and into a long sliding fall on firm surfaces.

     

    Example: You're likely to find reactive pockets of wind-drifted snow on Thursday. Cracking is one way to identify the reactivity.

    Photo: Heiko Stopsack

Avalanche Discussion

When temperatures cool before significant snow falls, as we're currently anticipating, Mt Hood typically experiences firm crusts and slide for life hazard. Melt-freeze conditions developed Tuesday and Wednesday, but with more cloud cover and minor amounts of fresh snow, many surfaces may not soften during the day. If the snow surface is firm and frozen, your ability to hold an edge and arrest a fall is paramount. Make sure you have the "sharps" and skills necessary to navigate the terrain you choose, and consider your exposure to a long sliding fall in that equation.

We're not sure whether lower elevations will refreeze. If they don't, use a bit of extra caution and moderate your slope angle if you find wet and unconsolidated snow surfaces. We generally expect that most of the wet loose hazard has played itself out, but even a small slide could ruin your day as the depleted snowpack exposes late-season obstacles.

NWAC forecaster Joe Dellaporta was out on the south side of the mountain Tuesday and Wednesday.  He found firmer and supportive snow conditions above 7000 ft on Tuesday and melt-freeze conditions down to 6500 ft on Wednesday as upper elevation winds increased into the moderate to strong range and temperatures cooled. Below, these elevations the snow became increasingly wet and punchy, but wet loose activity continued to decrease. Signs of limited natural wet loose activity on the upper mountain were visible from the weekend.  Last week's strong east winds had roughed up the surface at upper elevations, and signs of old wind effect were still visible. The warmth and consecutive nights of above freezing temperatures were starting to expose rocks along ridgelines and reduce the snow depth at lower elevations and southerly aspects.  Recent public observations tell a similar elevation-based story on Tuesday. Photos of the conditions during the prolonged warm spell in the gallery.

Observers reported natural avalanches in the Old Chute on the upper mountain on both the 17th and 16th, including one that caught and carried a person. On the 16th, an NWAC observer found wet snow below 7,500ft that became unsupportive at low elevations. 

If you head out, let us know what you find by submitting a public observation here! 

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