Bulletin d’avalanche

Mt Hood

Northwest Avalanche Center
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Danger d’avalanche

Fri
Alpin
2 · Modéré
Limite forestière
2 · Modéré
Sous la limite
2 · Modéré
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Périmé — ce bulletin a expiré 3 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

Your risk of triggering a shallow slab increase as snow and wind ramp up and conditions could become dangerous at upper elevations by the end of the day. Slabs will be easier to identify where they overly crusts but will entrain more snow where the overly and redistribute cold snow from the last storm cycle.  

Problèmes avalancheux

  • Wind Slabs

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

    In most areas, slabs we're expecting around 3-5" of snow to redistribute in exposed terrain. Where this snow overlies a melt-freeze crust in most terrain up to 7000 ft, enabling yoou to track the slab depth above the crust using a pole or probe. Where these slabs form 6" or deeper, you can trigger an avalanche on a steep slope that you should steer around. N aspects and upper elevations have a heavily wind-affected snow surface in most locations, but fresh slabs could be touchy where they overly any less wind-affected snow. These aspects could build an isolated large slab by the afternoon.. Wind patterns will be different with this storm as southerly flow focuses slabs on these same aspects on the northern half of the compass. Dial back your terrain selection as the day progresses or if you see evidence of fresh wind slabs avalanches, blowing snow, or shooting cracks. Once you enter wind slab terrain, steer around slopes 35 degrees and steeper. 

    (4/5/2023) Small explosive-triggered soft slabs in wind drifted snow.

    Photo: Joe Dellaporta

  • Loose Wet

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    1–1.5

    We're expecting light rain to fall on the snowpack up to 5500 ft. In most cases, this rain will fall on crusts and the surface snow will become wet and gloppy once the crusts break down. Anticipate this change if you're experiencing rainfall and move to higher elevations and out from under steep slopes. Take extra care near terrain traps like cliff bands and exposed stumps and rocks where a small avalanche could do more damage. 

    Example: You may see or trigger roller balls or small wet loose on steep slopes like the one in this photo Monday. 

    Photo: Kaitlin

Avalanche Discussion

We're heading into an active storm cycle with warming temperatures, denser snow, and rain on snow (at lower elevations) adding some uncertainty to the forecast. How quickly the snow levels rise and precipitation increases in intensity will influence how rapidly slabs form. With the added uncertainty, plan to dial back your terrain selection if you see anything that isn't in line with this forecast.

Another massive late-season storm brought 50-60" of snow to Mt Hood along with strong W and WNW winds (particularly on the E side of the Mountains). Intense winds and periods of heavy snowfall finally ramped down rapidly early Tuesday, but Mt Hood Meadows got impressive control results that morning.  The Accordian Avalanche released in near treeline terrain on an ESE aspect and was historically impressive, particularly for the elevation of the start zone. You can read more about it here. Avalanches such as this one are believed to be unreactive to human trigger moving forward. The slab failed on a softer layer just beneath the firm and very heavy slab with the weaker layer strengthening rapidly in the last 24 hours. Smaller soft slab pockets remained reactive to explosive triggers in control results on Wednesday. The sun came out to trigger some rollerballs on Wednesday and extended the elevation of the melt-freeze crust up to around 7000 ft on most aspects besides true north.

Last week observers reported weak snow associated with a crust that sits several feet below the snow surface. This layer was likely responsible for the isolated whumphs in the Gunsight Ridge area and propagating results( observation) near Vista Ridge. While isolated and unlikely, keep this information in mind especially if you find yourself traveling on higher elevation, northerly aspects.

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