Bulletin d’avalanche

Bridgeport Avalanche Center

Bridgeport Avalanche Center
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Danger d’avalanche

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

Points saillants

Strong winds and recent snowfall have created unstable snow conditions in and above the treeline. Terrain features loaded with wind slabs, such as leeward slopes, gullies, and isolated terrain features, could be sensitive to human triggers. Wind slabs and those deposited on weak, faceted snow will create a recipe for hazardous avalanche conditions. Consider a wide margin in your travel plan as terrain features such as start zones, cross-loaded slopes, and terrain traps will amplify the effect of even a small avalanche today. 

Problèmes avalancheux

  • Wind Slabs

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

    While traveling in and around avalanche terrain yesterday, we found a high degree of variability in the size and distribution of actively loading wind slab snow. Where we encountered the wind slab, it rested on top of weak, sugary, faceted snow. It broke apart easily to the touch and was scattered across terrain features.  Wind-driven snow loaded in terrain features like gullies, start zones, and leeward aspects will be reactive to human triggers today. The spatial variability of the snow distributed across the near-treeline and above-treeline terrain will require keen observation skills to recognize and avoid recently loaded terrain features. Consider testing the snow on small, representative, and inconsequential slopes for this problem before deciding to step into bigger terrain. 

Avalanche Discussion

New storm snow began to fall on the late morning of Thursday, December 12th. The storm came in cold with strong winds from the southwest and created fresh wind slabs in the Alpine and Near Treeline terrain. During our tour on Thursday, we found isolated pockets of wind slab that produced localized cracks around our ski tips. We also heard a whumpf and felt a settlement in an isolated pocket of NE terrain. Overall the new snow that fell was forming into a soft wind slab, which was breaking apart easily in my hand. 

Below that recently deposited wind slab was a variety of now-buried surfaces. North and East aspects around Sonora Pass held a faceted, weak, and sugary snowpack. South aspects had a strong surface crust and a more consolidated snowpack. West aspects were scoured and mostly bare ground.

The main concern for today is the recently formed windslab and the now buried faceted snowpack that it sits on. We will be monitoring how this strong snow (wind slab) is bonding with the weak snow (facets) over the next couple of days. An active weather pattern ahead will create much change in the snowpack. A warmer and wetter storm moves in early Saturday morning. 

We did not find enough recent new snow below treeline terrain to raise the danger to moderate. In and above the tree line, there is a high degree of variability in the size and distribution of wind slabs in the terrain. Looking only at SNOTEL sites, it can be hard to make sense of what an accurate distribution of snow looks like, especially when the snow is cold and dry and the wind is strong and gusty. With a bit more snow in isolated areas, the forecast could also read that human-triggered avalanches are likely today, referencing the North American Danger Scale.  However, it did not seem representative of the forecast area as a whole. As always, make your own terrain and snowpack assessments as this will be key to staying safe and managing avalanche problems in the backcountry. 

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