Boletín de aludes

Mt Hood

Northwest Avalanche Center
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Peligro de aludes

Wed
Alta montaña
3 · Notable
Límite del bosque
3 · Notable
Bajo el límite
2 · Moderado
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Desactualizado: este boletín caducó 4 years ago. Estás viendo condiciones pasadas, no el boletín vigente.

Lo esencial

745 PM Update: Increased size of potential avalanches for today. You can trigger a large and widely propagating avalanche on Tuesday, with the most dangerous conditions early in the day and near/above treeline. Note the wind slab distribution, a potential poor bond to the underlying crust, and any red flag signs of instability such as whumphs or shooting cracks.  Avoid all terrain 35 degrees to start the day, steering around wind-loaded slopes steeper than 35 degrees by the afternoon.

Problemas de aludes

  • Wind Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Likely
    Tamaño
    1.5–2.5

    1 - 1.5 ft of snow will be drifted into large, dangerous, and spatially contiguous slabs at higher elevations as strong W and WNW winds during the storm redistributed the snow significantly. Drifts could be 2-4 ft deep and may be either soft or hard slabs. Less wind-affected snow should be low density (given the cold temperatures) and right-side-up, given the cooling. A coating of powder may mask the more wind-affected layers. So if you experience firm or punchy layering, you're entering wind-loaded terrain and this snow structure is expected to be widespread on the lee sides of ridgelines.  Reports surfaced of a poor bond between the new snow and the crust, due to rapid cooling (likely near and above treeline) before precipitation arrived 2/13, while at lower elevations, the rain transitioned directly to snow and bonded well. Look for this transition as you travel (likely in the 5000-6000 ft range), noting the depth of the snow above the crust and how well it adheres in frequent shovel shear tests. If you find more than 8" of snow on top of the crust, it could fail as a storm slab on any aspect. We expect that these slabs will be most dangerous where wind loaded and where the new snow remains poorly bonded and ready to slide on the crust. Near and above treeline, your best bet remains to avoid all slopes, particularly along the lee sides of ridgelines, steeper than 35. Avalanches could release well below typical start zones given the strength of recent winds. Recent avalanche activity, whumphing, or collapses should all be red flag warnings to keep your terrain selection simple and low consequence. 

    While the more dangerous conditions will be near and above treeline, wind slabs snow sideways in some locations even below treeline on Monday. First thing in the morning, expect dangerous conditions at all elevations and ease into the terrain as you gain confidence on small test slopes and with frequent shovel shears. Limit your risk after a significant snow and wind event by steering around steep, wind-loaded start zones, convex rollovers, and large and consequential avalanche slopes.

    Example: Large explosive-triggered wind slabs in atypical alpine start zones low on the slope.

    Photo: Mt Hood Meadows Patrol

  • Loose Wet

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Possible
    Tamaño
    1–1.5

    Loose problems will be limited to wind-sheltered areas near and mostly below treeline. Not long after the snow shower activity tapers off, expect the mid-February sun to make an appearance. The sun will destabilize low-density snow surfaces despite the cold temperatures on aspects receiving relatively direct sunshine. As soon as you see the tell-tail sign of rollerballs, anticipate mostly small wet loose avalanches that may fail naturally on the slopes above you. These could entrain enough snow above the 2/13 crust to create fan-shaped debris piles that bury you in a depression or drainage bottom, so do take them seriously. Adjust your aspect to cooler, shaded terrain. This time of year, the impacts of the sun are starting to be felt onto E and W aspects, although we think that morning clouds will limit the impact on the former.

    Example: A Wet Loose avalanche occurred as a result of a tree bomb.

    Photo: Zack Novak

Avalanche Discussion

We're coming off a significant storm at Mt. Hood and the sun and fresh snow may be tempting, but cold temperatures willl help it will stick around long enough for you to ease into the terrain slowly. Tuesday is a good day to take stock of the rapidly changed surface snow conditions and to respect the capability of the recent strong to extreme winds to transport low-density snow. Recently formed and potentially large cornices may be sharp, overhanging, fragile and a hazard as you travel along the ridge or on the slopes below.

8-9" of snow fell accumulated on top of the 2/13 crust by the end of the day on Monday and we're expecting 1-1.5 ft by of storm snow by the time you enter the terrain on Tuesday. As previously mentioned, we have some concerns about the bond to this crust and it may be a player in larger and more widely propagating avalanches. The 2/13 crust was formed by very mild temperatures (in the 40s into above treeline elevations). This crust should be at all elevations but may be thin on higher-elevation shaded aspects. Focus your attention on the storm-related instabilities on and above the 2/13 crusts as we don't presently have a cause for concern below this interface. Below the 2/13 crust, you'll find mostly dry snow from storms between 2/3 to 2/8 that increased the snowpack 1.5 ft and contain thin inter-storm crusts on sun-affected aspects. 

If you get out into the storm, let us know what you see by submitting an observation.

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