Bulletin d’avalanche

Mt Hood

Northwest Avalanche Center
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Danger d’avalanche

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

Points saillants

You can trigger a wind slab avalanche on steep wind-loaded terrain at any elevation, with deeper and more consequential slides likely at mid and upper elevations.  Continue to mitigate the low-likelihood/high consequence threat of very large avalanches releasing from the upper mountain by limiting your exposure to canyon runouts even near forested terrain. 

Problèmes avalancheux

  • Wind Slabs

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

    We're in for another day of moderate to strong ridgeline winds with lots of cold dry snow to blow around at all elevations.  Continue to avoid steeper wind loaded terrain where you can trigger a wind slab avalanche.  Slabs will be deeper and more consequential at mid and upper elevations but don't be surprised to find shallower but potentially reactive slabs on open slopes and ridgelines at lower elevations. 

    Look for clues like blowing snow, textured snow surfaces and fresh cornices to help you discern which slopes have been recently loaded.  Red flags like shooting cracks in wind-drifted snow are signs you'll likely trigger an avalanche on nearby steep slopes.  Choose simple, less wind-affected terrain without overhead hazard. 

    Winds are a notch lower than earlier in the week but they are still loading the same slopes that have been pounded for several days.  It's becoming far less likely that very large and unsurvivable avalanches will release from alpine start zones, but we're not out of the woods yet.  Until this pattern breaks, give yourself an extra margin of safety and limit your exposure to canyon runouts even at lower elevations.  

    (2/29/2024)

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

    Photo: Koby Yudkin

  • Loose Dry

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

    At lower elevations and in more sheltered areas, light low-density snow has been incrementally piling up as we've shifted from a stormy pattern to a showery and colder regime.  While this is the type of snow most of us seek out, there are a few things to keep in mind to stay safe.  Use caution around very steep (40+ degree) terrain features like convex rollovers where you might trigger a loose dry avalanche.   Loose dry avalanches or sluffs, 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. 

    (3/25/2023)

    Dry loose avalanches on steep, north facing aspects. 

    Photo: Joe Dellaporta

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: 

We've received over 6.5" of water since Sunday with several feet of new snow piling up over this period.  Average wind speeds since this storm cycle started have averaged 20-30mph out of the SW or WSW with much higher gusts.  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 continued moderate to strong winds. 

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 new snow has not settled and deep snow immersion/tree wells are a real concern.  Ride with a partner and keep one another within sight. 

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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