Boletín de aludes

Mt Hood

Northwest Avalanche Center
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Peligro de aludes

Thu
Alta montaña
3 · Notable
Límite del bosque
3 · Notable
Bajo el límite
2 · Moderado
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Desactualizado: este boletín caducó 2 years ago. Estás viendo condiciones pasadas, no el boletín vigente.

Lo esencial

The day may start with borderline high danger as torrential rains move through the snowpack. As the day progresses, winds and cooling temperatures will start the healing process. Avoid large avalanche paths, runouts, and other open slopes steeper than 35 degrees until firm crusts form. 

Problemas de aludes

  • Wet Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Likely
    Tamaño
    2–3

    The most critical thing on your mind should be not getting smoked by an unsurvivable very large wet avalanche originating at upper elevations or even above NWAC forecast elevations on Mt Hood. In the case of the latter, these avalanches could release as a wind slab and become wet as it descends. Until the snowpack at upper elevations refreezes, the risk of these natural avalanches remains. Strong winds and cooling temperatures should start to refreeze the snowpack, so we think the risk of these types of avalanches generally tapers by the afternoon.  Best to avoid historical runouts of very large avalanche paths (including open slopes in the drainages) until you are confident that cooling temperatures are refreezing the start zones on the slopes above.

    Outside of these large avalanche paths, you can trigger small to large wet avalanches on steep open slopes. Rain rills will be a sign that the snowpack is healing. Check for poorly consolidated snow 6" or deeper (slush to the top of your boots) and if you find it, avoid open slopes steeper than 35 degrees.

     

     

    Example: As water percolates deeper into our snowpack,  very large avalanches could release off the upper mountain and run far into lower elevation drainages. 

    Photo: Peter Moore

Avalanche Discussion

We're coming out of a noteworthy storm cycle. 3 ft of dry snow sat above the 12/7 crust and 1-2" of liquid water will impact that dry snow by Wednesday morning. We don't know whether the water will pool on the crust, forming wet slabs, or simply entrain large amounts of saturated snow as wet loose avalanches. At best these avalanches will be unmanageable. At worst, they will be unsurvivable.

You can see from the weather timeseries that Mt Hood has been picking up 6-12" of snowfall each day this storm cycle before the changover to rain by around noon on Tuesday. The rain should drastically alter the snowpack structure moving forward. Visibility limited observations during the storm cycle, so we don't yet know whether very large avalanche activity has started on the upper mountain, but these are the types of storm cycles when it does...

During the cold snow phase of the storm cycle, a large natural avalanche was reported Monday on an ENE aspect at 8000 ft. This follows a size 2.5 natural avalanche reported by USGS on the slopes of Mt St Helens on Sunday. Mt Hood Meadows Pro Patrol reported triggering large and small avalanches with good propagation in wind-drifted terrain on Sunday. These hard wind slabs (P hard) broke 3-3.5 ft deep on a softer layer of storm snow.  We also heard two reports of avalanches on Mt Adams, one human-triggered and one natural. Both were around 8000ft on S to E aspects in wind-loaded terrain. These recent avalanches are a good reminder that these incremental storms are now building thick unstable slabs across the terrain, and it’s a good reason to step it back until the storm is wrapped up. 

Cornices are now large and as they build increasingly unstable, they may trigger slab or wet loose avalanches on the slopes below. 

Leading up to this storm, we had a variety of surfaces across the terrain. Solar aspects ( SW-SE) consisted of scoured surfaces and a stout sun crust. Shaded aspects held old wind-drifted snow, some weakening surfaces, and even some isolated surface hoar. These subtleties in the snowpack will likely become a thing of the past as rain saturates the snowpack at most elevations.

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