Avalanche forecast

Bridgeport Avalanche Center

Bridgeport Avalanche Center
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Avalanche danger

Mon
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
2 · Moderate
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Highlights

Strong southwest gale force winds combined with a wet-warm storm impacted the Sierra yesterday and into last night bringing a new dense layer of snow on top of the older, weaker snow.   Mid and upper elevations along the crest were mostly impacted by this heavier precipitation and wind loading.  Avoid traveling in and below avalanche terrain until evidence has proved that these new and old layers are bonding.

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–2.5

    Multiple weak faceted, depth hoar layers make up the bottom half of our snow pack.  While test pits the past couple weeks have proven these layers are becoming more resistant to shearing, not all tests pits were telling the same story.    The more snow on top of these layers is making them less likely to trigger, there are areas where human and snow machine triggering is still likely, especially with the new heavier snow layer. North aspect variations are still not seeing the sun (due to January sun angles), and those weak layers aren't healed (bonded) to adjacent layers.

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–2

    In the past 36 hours, our upper elevations have received over 2" of Snow Water Equivalent (general rule 1" of SWE = +-1' of snow) with varying wind directions and speeds sustained over 50 mph and gusts over 100 mph.  Leeward and protected slopes could possibly see up to 10' of new wind effected (wind slab) snow.  Leeward ridge lines will have new cornices formed and wind slabs in protected slopes.  Be aware that identifying these wind loaded zones will very difficult and give cornices a wide birth when traveling on ridges and avoid being underneath while on slope.

Avalanche Discussion

  • To put it simply,  specific zones of our forecast area have a stubborn weak layer underneath with a recently formed slab of of heavy snow on top.  We don't have enough data from users as our snowpack is difficult to access currently from most of our trail heads and usable snowy terrain is limited.  
  • Unlike our neighbors to the south ESAC and north SAC, we were not seeing the same reactivity from the basal (bottom) weak layers prior to this latest storm. Those weak layers are present and in snow pack tests we were seeing easy initiation and propagation, but not seeing the same on slope avalanche activity.  With that being said, this heavier-warmer layer of wind packed snow may be the missing piece to make our snow pack more reactive and widespread to natural and skier triggered slab avalanches.
  • Lower elevation below 8500' snow coverage is still very sparse especially on southern, sun exposed aspects. Clues to poor snow coverage is vegetation such as sagebrush poking through.
  • Northern aspects in the below treeline 8500' elevation bands, avalanches are possible where snow is deep enough as most, if not all of the snow pack has a rotten weak layer at the base.
  • Traveling into the mountains yesterday, lower elevation eastside of the Sierra Crest were not receiving much, if any precipitation.  But if you traveled up to 9k' or above, you probably experienced near white out conditions with the combo of gale force winds and precipitation.  Snowglobe like.
  • We weren't able to get into Above Tree Line (Alpine) yesterday as winds were too intense.  So we traveled to different parts of our Fx area to see at what elevations it was snowing and how the incoming storm varied from elevation and topographic differences.

Regions covered