Bollettino valanghe

Mt Hood

Northwest Avalanche Center
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Pericolo valanghe

Tue
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
1 · Debole
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Non aggiornato — questo bollettino è scaduto 4 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

You can still trigger a slab in wind-exposed terrain at any elevation, but be prepared for them on atypical aspects.  These slabs may be large and more dangerous at upper elevations.  Take advantage of excellent visibility to travel safely on scoured snow surfaces, steering clear of smooth, chalky, and pillowlike drifts on steep or poorly supported slopes.

Problemi valanghivi

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–2

    Strong to extreme NE winds formed slabs within 3" of low-density snow that fell Saturday. These winds were still transporting snow as of late Sunday. Slabs will be concentrated around atypical westerly and southerly aspects. Slabs are firm (1F to pencil hard), stubborn to trigger, and easy to identify with chalky, pillow-like drifts that you can visually identify. The feel of firm, hollow snow layers or cracking snow surfaces should also be a sign wind slabs are present under your feet. Winds have stripped the snow off many more typically wind-loaded E-facing aspects, which now have sastrugi or cross-loaded rippling patterns (see media gallery). The winds were so strong that they formed textured snow surfaces, variable snow conditions, and slabs 6" deep into more exposed below-treeline terrain and some drivers reported blizzard-like conditions on highway 35. You can trigger a slab anywhere you find wind-drifted snow 6" or deeper.  As these slabs become thicker and larger in horizontal dimensions near and particularly above treeline, they may become connected on the lee (west) side of ridgelines and more difficult to steer around. Also, be aware that some areas may have significantly more wind-deposited snow with more elevated slab hazards while wind-stripped areas will have lower hazard.  As always, terrain selection will be your key to safety on Monday. Identify and steer around wind-loaded slopes steeper than 35 degrees, recognizing that steep, unsupported rolls are most susceptible to avalanches. Below treeline, we expect low avalanche danger, but we still think you can trigger an avalanche large enough to knock you off your feet in extreme terrain features or may prove problematic above terrain traps such as gullies, exposed rocks, and creeks.

     

    (1/29/2023)

    Visually identify wind drifts such as these as you travel. In many cases, these will be opposite the prevailing wind direction as identified by bent trees and older cornices.

    Photo: Joe Dellaporta

Avalanche Discussion

No significant avalanches have been reported over the last few days, however, this may be a function of the extreme conditions which inhibited most people and ski area operations from accessing heavily wind-exposed terrain. 

On Sunday afternoon, Joe Dellaporta experienced bitterly cold temperatures and dangerous wind chills.  Wind-protected slopes below treeline may still harbor some preserved low-density powder. Most exposed aspects are either exposed to crusts, sastrugi, or wind slabs. Saturday's highly redistributed 3" snow event sits on old wind-affected snow layers or a thin, breakable melt-freeze crust (1/28) that may be present on sun-affected aspects near treeline. Below that, you'll find a firmer and widespread 1/27 crust which now has 4-6" of snow (on average) above it. The MLK crust sits around 2 ft below the snow surface. The crust is around 2" thick and partially decomposing with weakening/faceting snow just below it. This weakening snow may be worth watching the next time we get a significant precipitation event but is not believed to be a concern at this time.

Bitterly cold temperatures will linger through much of the day on Monday with some moderation in the afternoon. Light winds will make for much less extreme windchill values. Given the cold temperatures, pack some extra down and consider the added risk if something goes wrong if you head into more remote areas.

If you get out into the new snow, let us know what you see by submitting a public observation!

 

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