Boletín de aludes

Mt Hood

Northwest Avalanche Center
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Peligro de aludes

Mon
Alta montaña
3 · Notable
Límite del bosque
2 · Moderado
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

Winds will be strong enough to form reactive slabs at mid and upper elevations. A very large avalanche is not out of the question at upper elevations. Continue to stay off of and well out from under steep, potentially wind-loaded slopes, including runouts and canyon bottoms.

Problemas de aludes

  • Wind Slabs

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

    We're not out of the storm cycle yet. Snow showers continue to add 5-10" every 24 hours, adding plenty of fuel for gradually decreasing moderate winds to continue building slabs. Slabs Slabs at middle elevations will be in the small to large range, but could be very large and may break widely across terrain features at upper elevations. Human-triggered remain likely at upper elevations on Sunday, but isolated natural avalanches in heavily drifted upper elevation locations remain possible. Ascend the terrain with caution given the rapidly increasing danger with elevation. Continue to avoid steep or complex terrain at upper elevations and any terrain connected to start zones high above you - this includes long canyon runouts. For middle elevation slopes not connected to upper elevation start zones, you can steer or unsupported slopes with signs of recent wind-load loading. At these elevations, you're most likely to an avalanche in the immediate lee of ridgelines or where down-canyon winds cross-load gullies and actively deposit blowing snow. Red flags like shooting cracks in wind-drifted snow are signs you'll likely trigger an avalanche on nearby steep slopes.  

    (2/29/2024)

    Shallow wind slabs became more prevelant and reactive near and above treeline on both windward and lee slopes

    Photo: Koby Yudkin

  • Storm Slabs

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

    Low-density snow needs time to settle during and after periods of heavier snowfall. You can trigger a very soft storm slab on wind-sheltered steep slopes approaching 40 degrees. Hand pits and test slopes can help you evaluate mid-storm instabilities before you engage with terrain of consequence. If you find evidence of slab failure 8" or deeper, stick to slopes less than 35 degrees. 

    The low density snow may also fail as loose dry avalanches or sluffs. These may not be big enough to bury you but could knock you off your feet.  Getting swept off a cliff, or into dense trees or a tree well are real examples of how a small avalanche quickly becomes an issue in the wrong piece of terrain.  Natural dry loose avalanches are possible on very steep slopes following periods of heavier snowfall or on sunny slopes if the sun pops out for an extended stretch and temperatures rise. 

    Example: A small skier triggered storm slab avalanche. 

    Photo: Josh Hirshberg

Avalanche Discussion

Preliminary Accident Report: An avalanche accident occurred on Friday, March 1 near Darland Mt in the Ahtanum Meadows area (East South Zone). Two snowmobilers were involved in the slide. One rider was fully buried and killed. The avalanche occurred around 6600ft in a generally east-facing bowl. NWAC staff will visit the accident site on Saturday. Our deepest condolences to the family, friends, and community.

Mt Hood Discussion: 

 All of the new snow has not settled and deep snow immersion/tree wells (SIS) are a real concern in areas as additional snow piles up.  Ride with a partner and keep one another within sight. SIS resulted in a fatality on Friday in the Cascades. 

We've received over 6.5" of water since 2/25, with 70" of snowfall over this period and 8" of snowfall in the 24 hours ending 6 PM on Saturday.  Average wind speeds since this storm cycle started have averaged 20-30mph out of the SW or WSW with much higher gusts and have trended downward over the last few days.  We're in a much cooler and showery pattern for the short term, and we can expect showers to bring periods of low-density snow and graupel along with enough wind for moderate transport and mid and upper elevations. 

Snow surfaces stayed cold on Saturday with cloud cover. Observations were limited to lower-elevation terrain, where the snow was right side up and generally stabilizing. On Friday, the skies briefly cleared late in the day and Mt Hood Meadows pro-patrol was able to see deep crowns partially filled in on the upper mountain.  2 very large avalanches occurred in Heather Canyon, depositing debris several thousand feet down into Clark Canyon up to 50'(!) deep in places.  These avalanches likely released Tuesday night and again on Thursday morning.  It's unknown whether or not one or both slides occurred during avalanche mitigation due to storm conditions and poor visibility. It's a stark reminder of the massive avalanches that can happen on Mt Hood during or following a multi-day storm cycle and often during periods of poor visibility.  On Thursday, travelers at Pea Gravel ridge found strong winds and wind-affected snow, touchy wind slabs on test slopes, and new cornices as soon as they pushed up to near treeline.  On Friday, colder temperatures contributed to lower-density snowfall and loose dry avalanche concerns at lower elevations that were sheltered from the wind. 

All of the storm snow rests on the 2/24 interface.  Going deeper in the snowpack, a series of crusts and pockets of weak snow existed above the stout Early February Crust (EFC).  Prior to this storm cycle, these layers produced inconsistent snowpack test results and showed signs of gaining strength.  These layers are now buried several feet deep.  

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