Bollettino valanghe

Mt Hood

Northwest Avalanche Center
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Pericolo valanghe

Fri
Alta quota
4 · Forte
Limite del bosco
4 · Forte
Sotto il limite
3 · Marcato
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Non aggiornato — questo bollettino è scaduto 4 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

You may be able to easily trigger storm slabs at upper elevations - however as snow lines rise and precipitation changes to rain- the likelihood of you triggering a wet slab increases significantly.  A complicated weather forecast and overlapping avalanche problems should help keep your terrain selection simple. Avoid all areas where avalanches can start, run, or stop. 

 

Problemi valanghivi

  • Storm Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Very Likely
    Dimensione
    1–2

    Before the snow changes over to rain you may be able to trigger avalanches within the storm snow.  As precipitation falls, temeratures will continue to rise, which will cause storm slabs to be upside-down in nature and be quite sensitive to a human-trigger.  These may be widespread through the terrain at mid and upper elevations .  It won’t be hard to find hard-over-soft layering, cracking in the new snow, or test slopes failing easily.  So, your best bet will be to avoid all slopes greater than 35 degrees on Thursday. 

    (12/20/2021)

    Storm slabs like this may be easily triggered on Thursday at mid and upper elevations. 

    Photo: Andrew Kiefer

  • Wet Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    2–3

    Wet slabs are notoriously hard to forecast for and we have uncertainty regarding the weather forecast in-terms of when the snow will change over to rain and the amount of precipiation we may see. What we do know is snow levels are on the rise - precipitation will change over to rain eventually- and we currently have a dry snowpack in most places.  Additionally, we have weak layers of surface hoar and facets adjacent to a crust in specific mid-elevation areas, all of which could be interfaces that wet avalanches fail on.  As water percolates into our dry snowpack, the liklihood of triggering a wet slab increases significantly .  

    Any slopes steep enough to avalanche should be suspect.  Thursday will be a good day to avoid all areas where avalanches can start, run, or stop.  Traveling in canyon bottoms will not be the best place to be, since very large avalanches could potentially run through these areas.  

    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

On Wednesday morning the Mt Hood Meadows Pro Patrol found stubborn wind slabs and generally an unreactive snowpack during avalanche control work. I also found similar conditions on my calm morning tour up Timberline.  Overall it appears the wind slabs have healed and are mostly unreactive.

Thursday will be a very different story as a warm front associated with an atmospheric river lifts north.  This will bring rising freezing levels and precipitation in the form of snow changing over to rain.  By Thursday afternoon, Mt Hood will be flirting with 9000 ft freezing levels. 

 

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