Bollettino valanghe

Swan Range

Flathead Avalanche Center
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Pericolo valanghe

Tue
Alta quota
4 · Forte
Limite del bosco
4 · Forte
Sotto il limite
3 · Marcato
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In sintesi

An AVALANCHE WARNING has been issued for all zones due to very dangerous avalanche conditions. Below about 6500 feet, a wet snow avalanche cycle is ongoing due to above-freezing temperatures and rain.   Heavy snow and powerful winds continue to form thick, unstable slabs at upper elevations. Today's slides will entrain substantial snow, resulting in very large destructive avalanches with debris capable of reaching the valley floor. Travel in avalanche terrain is not recommended. 

Problemi valanghivi

  • Loose Wet

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Very Likely
    Dimensione
    1–3

    Overnight rain and moist snowfall likely developed a natural wet snow avalanche cycle at low and middle elevations that will continue through the day. Rising temperatures and light precipitation may expand this hazard to upper elevations. Slides will be large and dangerous with entrainment of the recent 2-3 feet of snowfall probable. Debris may travel long distances and impact the valley floor.

    Snow falling from tree branches, rollerballs, and encountering a mushy snow surface are all signs the snow is warming, weakening, and becoming moist. 

    Wet slabs may occur in locations receiving mainly rain. Water percolating into the snowpack could reach and lubricate a weak layer, resulting in a large avalanche.    

    Traveling in or beneath avalanche terrain, including path runouts, is not recommended.

    This is the size of wet loose slides expected with our current storm. We expect them to run to the valley floor in many locations.

    Photo: Carmel Johnston

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Very Likely
    Dimensione
    1–3.5

    Above roughly 6500 feet, heavy snow and strong winds continue forming thick, sensitive slabs on leeward slopes. These will be found near ridgelines and in cross-loaded mid-slope locations. Large, destructive natural avalanches will likely occur throughout the day, with human-triggered avalanches very likely. Debris may travel long distances and into areas with wet snow, resulting in a very large destructive avalanche that may reach the valley floor.

    In sheltered terrain, slabs formed in last night’s dense snowfall rest on a surface of less dense recent snow. This upside-down near-surface structure is unstable and will result in natural avalanches in all aspects. 

    The hazard will increase throughout the day as temperatures warm, dense snow falls, and the wind blows, resulting in a more cohesive snow surface. 

    Cracking under your feet or machine indicates you have found a sensitive slab. A stiffer surface that does not allow your boards or machine to sink into is a sign of cohesive snow. Traveling in or beneath avalanche terrain, including path runouts, is not recommended.

    (3/2/2023)

    Thick, unstable wind slabs will be found on upper-elevation slopes open to the wind. These are likely to fail naturally throughout the day. 

    Photo: md

  • Persistent Slabs

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

    The ongoing powerful storm may awaken dormant, weak layers buried several feet below the surface. These layers are gaining strength, and a general lack of recent instability is associated with them. Generally, initiating an avalanche requires a large trigger, like a cornice fall or heavy wind loading. Both of those will occur today, and we have increased the likelihood of a slide to possible. The most likely location for a triggered slide is in steep, rocky terrain where the wind has left a slab of variable thickness.  

    Mitigate this hazard by staying off of and out from under steep slopes. 

    This is the type of terrain in which a Persistent Slab avalanche may occur. Steep, rocky terrain with a variable slab depth.

    Photo: Mark Dundas

Avalanche Discussion

We have issued an AVALANCHE WARNING for the entire forecast area through 0600 Tuesday morning. A warm, powerful storm has deposited over 1 inch of SWE (Snow Water Equivalent) in many locations. This precipitation has been accompanied by gale-force winds, including a gust of 77 mph at the Aeneas Ridge wind station. Rising temperatures and rain likely created a widespread wet snow avalanche cycle on all aspects at low elevations and into the middle elevations overnight. The wet snow hazard may expand to the upper elevations later today. Strong winds will form thick, unstable slabs above the snow line throughout the day.

 

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