Bollettino valanghe

Northwest Mountains

Crested Butte Avalanche Center
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Pericolo valanghe

Thu
Alta quota
4 · Forte
Limite del bosco
4 · Forte
Sotto il limite
4 · Forte
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In sintesi

A potent storm is forecasted to drop significant amounts of snow coupled with strong westerly winds on Wednesday and Wednesday night.  The avalanche hazard may reach HIGH as early as this afternoon or more likely after sunset.  Carefully monitor new snow accumulations; once you observe around 10 inches of new snow, expect that that avalanche danger is quickly trending towards HIGH.  As the new snow stacks up, you will need to manage overhead hazards as some drifted start zones could run long distances before days end.  Avalanches could break in the new snow or on deeper weak layers.  If the snowfall forecast verifies by this afternoon or evening then travel on or underneath avalanche terrain is not recommended.

Problemi valanghivi

  • Persistent Slabs

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

    Another loading event Wednesday and Wednesday night will stress Persistent Weak layers in the middle and at the bottom of the snowpack.  Slabs will range from 2 to 4 feet in sheltered areas and far greater in drifted terrain.  If the weather forecast verifies expect that some avalanches could break deeply in the snowpack.  Persistent Slabs can be triggered from a distance or from below the slope, so consider the terrain that is above you.

    1/31: Natural persistent slabs that were triggered on Sunday by solar warming

  • Storm Slabs

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

    As the snow piles up to around 8 inches or greater, expect Storm Slabs to develop.  The new snow is falling on a variety of surfaces including melt/freeze crust on sunnier slopes, small-grained facets on some northerly slopes, or decomposing fragments on higher elevation shaded slopes.  By late in the day or early evening, Storm Slabs could reach large (D2) in size.  

    Storm Slab avalanche from earlier this winter.

Avalanche Discussion

A significant storm will impact the area today and tonight.  Snowfall numbers are expected to push the avalanche danger rating to HIGH (Level 4 of 5) during this storm.  There is uncertainty about when this will occur.  The best estimates are that sometime around sunset or a bit later, the new snow totals will reach the critical threshold and start producing natural avalanches with human-triggered avalanches becoming very likely.  If you head into the mountains first thing this morning, the danger will be much like it was yesterday, but as the new snow stacks up throughout the day the danger will rise.  A reasonable number to clue you into the increasing danger will be around 8-inch mark.  As the new snow accumulations creep into double digits then the hazard is starting to get closer to HIGH.  Keep in mind that westerly winds will transport the new snow on to leeward features throughout the storm and will start to form shallow slabs at these locations first.  Weak layers buried deeper in the snowpack are keeping forecasters worried; reports of collapses and remotely triggered avalanches have trickled in since the storm over the weekend, and many slopes were already sensitive to the weight of a person.  Many slopes on the Persistent Slab rose are near the teetering point prior to this storm, so it should be expected that if this storm delivers there will be a widespread avalanche cycle with some avalanches breaking in deep, old weak layers.  If you head into the hills today plan for the increased hazard and have a plan in place to deal with significantly more dangerous avalanche conditions at day's end.  Consider what terrain you may need to cross below on your way back home once the danger has increased.

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