Bulletin d’avalanche

Mt Hood

Northwest Avalanche Center
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Danger d’avalanche

Fri
Alpin
3 · Marqué
Limite forestière
3 · Marqué
Sous la limite
1 · Faible
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Périmé — ce bulletin a expiré 5 months ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

You can trigger a large slab in wind loaded middle or upper elevation terrain on Thursday. Strong winds may load start zones, mid-slope convexities, or even morraines near canyon bottoms. Give steep, lee slopes another day to gain strength and seek safer riding conditions on wind-sheltered slopes.

Problèmes avalancheux

  • Wind Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    1–2

    Thursday will be the final day of a 3-day storm cycle. Although snowfall peaks Wednesday afternoon through the night, wind speeds likely peak on Thursday. We're expecting significant wind redistribution throughout the day on Thursday, maintaining slab reactivity as slabs also increase in size. Focus on the degree of fresh and recent snow transport rather than decreasing snowfall rates. If you see large plumes of snow coming off ridgelines, slabs on the slopes below will be fresh and reactive. Even if wind loading dies down, drifts will be recent and need more time to settle out. Look for fresh, sharp cornices overlooking suspect slopes. Slabs may form in the lee of ridges or well down on the slope, such as on poorly supported rolls in the terrain. In some cases, extreme wind gusts could scour start zones and deposit most of the snow down in canyon bottoms. Gauge the depth of the snow above the 3/13 crust and steer around any steep slopes where you suspect deeper deposits. Slabs could fail on density interfaces above the crust or pull out down to the crust. The crust has a slick and more concerning bed surface in upper elevation terrain, where we are also expecting thicker drifts, combining to form larger and more widely propagating avalanches. Give yourself an extra margin for safety, limiting your exposure to activly loading slopes above you, which could produce isolated natural avalanches.

    At lower elevations, we're looking at shallower amounts of new snow above the crust. Winds may form isolated slabs near more exposed ridgelines. Steer around lens-shaped pillow-like drifts on steep slopes.

    Example: Heavy drifitng along Pea Gravel Ridge

    Photo: Joe Dellaporta

Avalanche Discussion

Tuesday morning through Wednesday afternoon, Mt Hood Meadows picked up 0.87" of water equivalent. This only translated into around 2-4" of snow at the ski area base. However, at middle elevations, snow totals pushed into the 4-8" range, with greater amounts at upper elevations. The recent snow sits on a widespread 3/31, which represents a "new ground" in the terrain and is particularly slick at upper elevations. Moderate ridgeline winds redistributed the recent snow to produce large and reactive slabs. On Wednesday morning, the upper elevations of Mt Hood Meadows produced two explosive-triggered avalanches: D2 in Silver Bowl that ran full path with a 6-18" crown depth in addition to a D1.5 in A-zone. Given the mild temperatures, there was a significant decrease in slab reactivity in middle elevation terrain.

We're still expecting 0.6-0.7" of water equivalent with a cooling trend lowering snow levels to around 2500 ft by Thursday, likely producing a right-side-up snow profile except in wind affected snow. In wind sheltered terrain, dry loose avalanches are possible, particularly on shaded aspects where you could get the snow running with you on a very steep slope. Loose avalanches can get you into trouble if they push you into unfriendly terrain. Snow showers should decrease as the day progresses, but winds will remain moderate to strong, limiting the potential for wet loose avalanches if the sun comes out. 

Although the snow conditions should be significantly improved by Thursday, windward aspects and ridgelines are likely to be stripped of dry snow above the 3/31 crust, potentially exposing slick surfaces. Make sure you have the tools and the skills to arrest a fall on steep, crusty slopes.

Expect a plethora of travel hazards at lower and middle elevations due to historically low snow.  Fresh snow is likely to obscure hazards, but not materially change the underlying poor coverage.

Are you heading out?  Let us know what you see by submitting an observation here or on the AvyApp.

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