Bollettino valanghe

Mt Hood

Northwest Avalanche Center
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Pericolo valanghe

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2 · Moderato
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Non aggiornato — questo bollettino è scaduto 6 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

Conditions are generally stabilizing, however, shifting wind directions will finally allow warm temperatures to weaken existing soft snow surfaces. At lower elevations, the morning's cold dry snow could produce wet avalanches by the afternoon. At upper elevations, isolated slopes could still hold lingering wind deposits capable of avalanching. Although the weather forecast looks great, be prepared to make your own assessments as you travel. Unique conditions will exist at different elevations and aspects.

Problemi valanghivi

  • Loose Wet

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

    East winds have kept snow surfaces cool and prevented the possibility of loose wet avalanches despite temperatures reaching over 40F at 7300'! There is some uncertainty about rapidly the winds will shift to westerly flow in the next 24 hours. When cool east winds are replaced by mild west winds, the warm ambient air temps will have a rapid impact on any soft snow surface. Sheltered slopes still holding fresh snow are the most likely to experience loose wet avalanches. Firm and scoured snow surfaces will likely not warm rapidly enough for loose wet avalanches to be a concern. Let the behavior of the snow surface guide your decision making more than the thermometer. Watch for signs of the snow becoming "heavy" and roller balls or pinwheels forming on the surface. This is evidence that you could trigger a loose wet avalanche. Steer away from slopes in direct sun which are steeper than 35 degrees if you see signs of warming surface snow.

  • Wind Slabs

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

    Very strong winds built shallow but reactive wind slabs Monday. Reports from Tuesday suggest that winds were strong enough to redistribute the snow into a patchwork of small wind slabs rather than thicken existing wind slabs. Wednesday, the east wind continued to keep the snow surface cool and wind transport active despite above freezing air temperatures, so shallow recently formed wind slabs may exist at upper elevations. Use visual clues to identify areas where wind slabs may exist such as slopes directly below cornices, pillow-like drifts, and convex slopes or gullies. Use caution where you see evidence of freshly wind transported snow and navigate around wind-loaded features especially where slopes are greater than 35 degrees.

    Blowing snow, firm and textured snow, and cornice formation are all evidence that wind slabs are likely to be forming on lee slopes.

Avalanche Discussion

Cold air entrenched in the valleys and blowing in from the east kept snow surfaces cool Wednesday and encouraged active wind transport at middle and upper elevations. That will change Thursday as the winds shift to mild and westerly. Let the behavior of the snow surface guide your decision making more than the thermometer. 

Last weekend's beautiful weather left snow surfaces at most elevations and aspects firm either by wind scouring or the sun's melt/freezing action. Monday's powerful winds and heavy snow deposited an erratic arrangement of snow depths and textures. Areas in the alpine are scoured bare or packed with dense wind affected snow. At lower elevations, sun-exposed slopes have begun to feel the effect of rising temperatures while shaded slopes still hold cold, poorly bonded snow.

The bottom line is that although conditions are generally stabilizing, vastly different conditions will be found at different elevations and on different sides of the mountain.  At lower elevations recognize where sun-affected snow is beginning to form roller balls and pinwheels suggesting you could trigger loose wet avalanches on slopes steeper than 35 degrees.  Recognize when you transition into wind affected terrain and navigate around cornices and steep pillow-like drifts.

As we head into a week of high pressure remember that NWAC does not have enough consistent and reliable information to accurately forecast for the uppermost slopes of Mt Hood. If you choose to travel in the highest alpine terrain, carry avalanche rescue equipment and be prepared to make your own assessments.

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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