Lawinenlagebericht

Continental

Valdez Avalanche Center
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Lawinengefahr

Hochgebirge
3 · Erheblich
Waldgrenze
3 · Erheblich
Unterhalb
2 · Mässig
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Veraltet — dieser Lagebericht ist 3 years ago abgelaufen. Du siehst vergangene Verhältnisse, nicht den aktuellen Bericht.

Kernpunkte

The avalanche hazard is Considerable above 2000 feet and moderate below.  Human triggered avalanches are likely 1-2 feet in depth above 2000 feet especially where the wind has moved the new snow into deeper pockets.  Careful route finding and conservative terrain choices will be necessary for safe trave in avalanche terrain today.

Lawinenprobleme

  • Storm Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Likely
    Größe
    1–2

    Our forecast area received around a foot of snow overnight.  Snow totals appear to be fairly similar across acoss our forecast area along the road with Valdez receiving the higher end at 12 inches, Thompson Pass 8-12 and 46 mile 9 inches.  Winds were blowing from multiple directions overnight with predominate SW-SE winds recorded at the upper elvation Nicks snotel.  Winds on Thompson pass were out of the north during the middle of the night and switched to southerly in the early morning hours.  Expect to find multiple aspects loaded by the wind.  

    This new snow will need time to settle and bond with the underlying snowpack.  In some areas there is a layer of buried surface hoar that is now buried by 18-24 inches of snow.  Where this layer exists expect storm slabs to be more sensitive to human triggers.  Buried surface hoar exists below 4000' in areas that were protected from the strong outflow winds of last weekend.  The strength of winds last weekend would have destroyed this layer in most locations, although is still a concern in very specific areas.  It is likely that areas in close proximity to Thompson Pass will not have buried surface hoar.

    Moderate to strong winds overnight will have created loaded areas where the storm snow is stiffer, deeper and more sensitive to human triggers.  Expect to find instability on wind loaded slopes steeper than 32° , convex terrain and cross loaded gullies.

    Pay attention to the pattern and amount of wind redistribution.  How strong was the wind?  Which slopes are loaded?  Use small incosequential test slopes and hand pits to determine how well the new snow is bonded.  Signs of instablility include shooting cracks, collapsing and natural avalanche activity.

     

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  • Persistent Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    1.5–2.5

    New snow and wind has added stress to a potential persistent weak layer that may exist in isolated locations at high elevation in the Continental zone.

    A natural avalanche was observed on 12/1 around 5400' on The Shovel "40.5 mile peak" that had a very wide propagation.  Crown not only included the entire start zone, it wrapped around a rocky terrain feature indicating a persistent layer as the failure plane.  Crown width estimated at 1500' mapped on google earth, depth was difficult to tell but probably in the 1-2 foot range.  A few other naturals were visible on upper ramps of 40.5 mile, although they were not nearly as wide.

    It is possible this weak layer is isolated to high elevation areas (above the Thanksgiving rain crust) in the Continental zone.  This layer may have developed during the clear and cold period just before the Thanksgiving warmup.  It is likely this layer was only  preserved in areas that were sheltered from the strong winds that accompanied the 11/20 cold spell.  A lack of natural activity from other areas would support this idea.  Below 4500' this layer was likely rained away and in wind exposed terrain above 4500' likely destroyed.

    On 12/7 this layer was not present at 4200' on Crudbusters and has not been found in other snowpits or reported by others.  Therefore, there is a large amount of uncertainty dealing with distribution and sensitivity of this layer.  More information will need to be gathered.

Avalanche Discussion

Our mountains have received 18-24 inches of new snow in the last 72 hours along winds that have been blowing in multiple directions.  This snow has fallen on a generally stable snowpack which should allow the new snow to heal and bond well, but this takes time.  It is likely that unstable snow will exist today on steep wind loaded slopes, convex terrain and crossloaded gullies.

Pay attention to the sensitivity of new snow and the amount of wind redistribution that has occured.  Try to be patient today, use terrain progression as a tool to assess how well the new snow has bonded before jumping into consequential avalanche terrain.

A potentially dangerous layer of surface is now buried by 18-24 inches of new snow in very specific areas.  Where present expect storm slabs to be more sensitive.  See avalanche problem above for distribution.

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