Bollettino valanghe

Seward and Lost Lake

Chugach National Forest Avalanche Center
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Pericolo valanghe

Mon
Alta quota
3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
3 · Marcato
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Non aggiornato — questo bollettino è scaduto 7 months ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

Avalanche conditions are dangerous. It is likely a person will trigger an avalanche on weak layers of snow buried 1.5 to 3' deep. People have recently triggered similar avalanches remotely from low angle terrain connected to steeper slopes, and yesterday's storm has pushed the snowpack closer to its breaking point. 

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SPECIAL ANNOUNCEMENTS:

We have issued a Special Avalanche Bulletin through the National Weather Service, in effect from 6 am today through 6 am tomorrow.

Problemi valanghivi

  • Persistent Slabs

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

    Recent avalanches: We saw multiple natural avalanches in the Snug Harbor area earlier last week, which appear to have failed on a shallow weak layer. There was also one small but noteworthy snowmachine-triggered avalanche on a wind-loaded bank in the Boulder Creek area.

    We are expecting a few days of quiet weather following this most recent storm event, which has added more weight to a fragile snowpack. This storm is the latest in a series of storms this month that have slowly added more stress to several buried weak layers. This is when avalanche accidents happen. The potential size of avalanches is slowly increasing, but we have not seen a big enough storm event to break these weak layers and produce a widespread natural avalanche cycle. Despite the lack of widespread natural activity, there are multiple crystal-clear signs that we have an unstable snowpack:

    1. We've seen natural and human-triggered avalanches failing on a weak layer of facets now buried 1.5 to 3' deep. The extent of natural activity during the most recent storm is unclear, but there were human-triggered avalanches prior to the storm in the Boulder Creek area last Wednesday.
    2. People have consistently reported experiencing large collapses as they travel in Girdwood, Turnagain Pass, and Summit Lake, with multiple people getting collapses on established skin tracks. The structure is very similar in the Seward/Lost Lake zone.
    3.  Most of the snowpit test results from the past three days have been very unstable.

    This most recent storm event came in warmer and windier than any of the smaller storms that we've seen this month. For the first time, we now have a denser, more cohesive slab on top of our weak snowpack. This is the piece of the puzzle that has been missing up until now. At this point, we should assume that most slopes are primed for an avalanche and are just waiting for a trigger. There is a very good chance that avalanches may be triggered remotely, from lower angle terrain below steeper slopes. These will be most likely on wind-loaded slopes, but there is a good chance a person will be able to trigger an avalanche in any steep terrain, whether it has been hit by the wind or not.

    This is a dangerous setup that we are not used to dealing with in our region. The weak, faceted snow that developed during December will remain reactive much longer than the typical storm and wind slabs that we typically manage. This type of weak layer is responsible for the majority of fatal avalanche accidents in our area. Approach terrain cautiously today, and consider managing this problem by avoiding traveling on or below steep slopes.

    Observed storm totals since Friday night are listed below:

      Snowfall Snow Water Equivalent (SWE) Girdwood 12-14" 1.4" Portage 10-12" 0.9" Turnagain Pass 6-8" 0.6" Summit Lake 3" 0.3" Seward 12-14" 1.2"

     

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