Bollettino valanghe

Mt Hood

Northwest Avalanche Center
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Pericolo valanghe

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

Small wet avalanche activity will peak early in the day. As temperatures cool and strong winds transport fresh snow, wind slabs will become easier to trigger as the day progresses. Stick to terrain less than 35 degrees if you find 6" of wet slush or encounter drifted snow fully obscuring the pervasive rain rills.

Problemi valanghivi

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–1.5

    Once the rain transitions back to snow, transition your attention to dry snow avalanches and slabs that form as the wind loads lee slopes. Wind slabs may not become a problem until late morning or the afternoon, but once you have several inches or more of fresh snow in your terrain, anticipate shallow slabs on wind-loaded slopes. Actively blowing and drifting snow indicates the growing instability in your terrain. Cracking indicates you are moving onto a slab that you can trigger once it becomes sufficiently thick. If you can't see the rain rill texture in the terrain, wind slabs have likely formed and are large enough to produce an avalanche. If you suspect a problem, steer around wind-loaded slopes steeper than 35 degrees.

    Example: Wind slab below corniced ridgeline.

    Photo: Jeff Zimmerman

  • Loose Wet

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

    Rain falling on the snow should help soften firm surfaces, resulting in slush as the water pools in the upper snowpack. Your risk will be greatest during mild weather and moderate rainfall during the morning hours. If you find slushy snow that you can sink into up to your ankle, small wet loose avalanches may be human or naturally triggered on slopes steeper than 35 degrees.  Pay attention to terrain traps below you such as creeks and steep slopes that you may pass beneath as you travel.

    Example: Wet loose avalanches.

    Photo: Public Observation

Avalanche Discussion

Mt. Hood can expect just under an inch of water to fall through the day on Thursday. Much of this will fall as rain below 7500 ft. But, we expect 2-4" of snow to fall above treeline with 1-3" likely falling near treeline as temperatures drop behind the cold front. The snow will accumulate on an uneven surface of refreezing rain rills. 

Mt. Hood picked up around 0.15-0.20" of water equivalent as early morning snow changed to light rain near and below treeline on Wednesday. Perhaps an inch or two of wet snow fell above 6500 ft.  Moderate winds may have drifted that snow, building shallow slabs at the highest elevations. Several inches of wet snow that fell Tuesday fully froze, adding to the pervasive crust Tuesday night.

A stretch of sunny skies and spring-like weather MLK weekend resulted in a significant thaw as temperatures rose into the 40s. During the spring-like days, small wet avalanches ran on the sunniest slopes. A few cornices sagged and fractured as well. Many glide cracks opened up, but only one turned into an avalanche that we know of (observation).  Surface hoar was observed as well, but rain, wind, and sunshine likely subsequently destroyed this layer.  Those who took advantage of the fair weather to climb high on Mt. Hood observed falling rime ice began mid-morning, and observers witnessed several large chunks fly down popular southside climbing routes. A few moats, glide cracks, and melting fumaroles were additional hazards to avoid on the upper mountain. Textured, icy surfaces and rain rills were found in many places and will underly any new snow arriving on Thursday.

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