Avalanche forecast

Bridgeport Avalanche Center

Bridgeport Avalanche Center
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Avalanche danger

Sun
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
3 · Considerable
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Out of date — this forecast expired 3 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

A fast-moving storm will bring strong wind and new snow causing the danger rating to rise throughout the day.  This wind-loaded snow could overwhelm our fragile snowpack which consists mostly of weak faceted grains.  It will be possible for avalanches to step down to the bottom of the pack, even a small slide could have a big consequence. Careful snowpack evaluation and conservative terrain choices will be key to avoiding these problems. 

Avalanche problems

  • Wind Slabs

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

    The wind that has been blowing from the North and East will shift direction to the West and Southwest, causing fresh slabs of snow to form on leeward aspects. With ample amounts forecasted, this new snow will mix down into below-treeline terrain, where previously very little snow was present. Cross-loaded gullies and convexities in the terrain will be especially suspect to this wind slab problem. The new snow is forecasted to come in cold and strong wind is expected to mix down to valley floors. 

  • Persistent Slabs

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

    Persistent Slabs are tricky as a whole and it is unknown just how much new loading on Saturday will tip the scale and cause the entire snowpack to slide. The loose sugary snow at the bottom of our pack is well documented and the structure of the pack overall is less than ideal.  Depending on the overall snowfall totals we receive will determine if we have a large-scale natural avalanche cycle in our northern aspects. If we don't get the necessary weight to clear out the large-grained faceted snow at the ground, the problem will linger like a landmine in the snowpack, waiting for a human trigger to cause a release.  This problem has been in our forecast area for weeks and a variety of crusts and snow densities have sat on top of it without much feedback.  In most areas, our pack is shallow (< 100 cm), cold, and loose. The new snow is also expected to come in cold which will make a natural avalanche cycle hard to predict as it might not have the necessary weight to clear out the problem snow at the bottom of the pack. 

  • Loose Dry

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

    Snowfall rates of 1-3" per hour will cause rapid loading in the next 24 hours and test the strength of the snowpack. When snow falls this fast on steeper slopes it does not have the necessary time to bond to the older snow that it fell on.  Currently, there is ample amounts of loose and unconsolidated snow in and around treeline terrain near Sonora Pass. Cold temperatures have been driving the faceting process (near surface faceting) keeping our existing snow loose and dry on Northern aspects.

     

Avalanche Discussion

With a winter storm warning in effect, a fast-moving shot of cold and dry snow is expected to hit our forecast area this morning. The new snow will be accompanied by winds from the West and Southwest, with 100+ mph gusts over the Sierra Crest. We expect a lot of snow to be blowing around and creating a scene out there, possibly blizzard-like conditions at times. When the wind blows fresh snow around, wind slabs will come with it. These will be sensitive to triggering and conservative terrain choice will be key. The other big problem that will not be so clear is the persistent slab problem. When the problems get complex it can be a good habit to go back to the basics, strong wind-driven snow is going to be placed on top of weak snow. When strong snow is placed on top of weak snow, the "house of cards" could collapse.  Yet it is often never that simple and the new snow will stack up on top of the fragile pack, waiting for a trigger.  Over time this problem does heal but it often takes more time than we think it does and we can get lured into a false sense of security as surface clues won't tell us much about the poor structure and large faceted grain sizes at the bottom of the pack.

Snowfall distribution in our forecast area is anything but uniform right now. Outside of Sonora Pass, it is almost non-existent in spots.  Earlier this week, Sonora Pass received 12-16 inches of new snow while other areas further south picked up a few inches. January more often than not has been a dry month for us, however, this January does not seem to be shaping up that way. The storm door looks to be open with long-range weather models showing an active pattern ahead. 

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