Bulletin d’avalanche

Bridgeport Avalanche Center

Bridgeport 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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Points saillants

Another Sierra storm making its debut this morning.  Gale force winds, new snow and a potential lingering deep weak layer.  Intensity of the storm will increase, throughout the day and with it, the danger.  Make your margins wider and avoid steep leeward terrain.

Problèmes avalancheux

  • Wind Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    1–2.5

    Strong gale force South and South West winds and dense warm snow has been actively blowing and snowing overnight.  This new storm layer will be landing on a surface crust layer from warmer temps over the past several days.  There will be scoured zones and pockets of wind loaded wind slab.   As the accumulation increases today, the danger and reactivity of these slabs will increase.  Avoid steep, wind loaded slopes on leeward sides of ridges and cornices.  

  • Deep Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Unlikely
    Taille
    1.5–3.5

    Deep within the snowpack exists weak sugary snow near the ground. This rotten snow is from early season storms in November that were sheltered on high elevation  shaded aspects. Now that  this layer is buried deep within the snowpack it is difficult to trigger, but if it does slide you can expect a very large avalanche to occur. As we investigated  the 2 human triggered slides from last weekend a common factor was that both avalanches occurred near the ground just below an ice layer with 2-3mm facets were present and  both avalanches were triggered in a shallower part of the snowpack and propagated far and wide across the entire slope. 

    As more snow falls and diurnal temperatures cycle, this layer will be harder to trigger. We will see how the new snow layers weight will effect the weak layer in its specific location.  As of last week, we only saw these large avalanches on upper elevations, on leeward aspects on wind loaded slopes, human triggered.

Avalanche Discussion

A couple of complexities to be aware of in the snowpack:

  • New wind slabs, on top of old wind slab on top of rain crust.  
  • Temperature changes over the past 24 hours, during the storm creates minute changes in density of the snow.  We are concerned with heavier, dense snow on top of lighter snow.
  • Old snow weak layers further down in the base of the snowpack are still suspect and verdict is out on how the new snow load will respond.  It may not respond until human triggered.  
  • (12/28/2025)

    Large, loose facets at the bottom of the snowpack at Latopie Lake

    Photo: Bridgeport Avalanche Center

     

  •  Spatial distribution of an avalanche problem, from Statham et al. (2018)

Régions couvertes