Lawinenlagebericht

Maritime

Valdez Avalanche Center
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Lawinengefahr

Hochgebirge
3 · Erheblich
Waldgrenze
3 · Erheblich
Unterhalb
Keine Stufe
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Veraltet — dieser Lagebericht ist 9 months ago abgelaufen. Du siehst vergangene Verhältnisse, nicht den aktuellen Bericht.

Kernpunkte

The avalanche hazard is CONSIDERABLE at all elevations.  Strong winds combined with snowfall has increased the potential for human triggered avalanches up to 3 feet in depth.  Human triggered avalanches are likely, and natural avalanches are possible.  Low elevations of the Maritime zone have no hazard rating due to insufficient snow.

In addition to avalanche hazard, the risk of frostbite will increase through the weekend on Thompson Pass.

Lawinenprobleme

  • Wind Slabs

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

    The primary avalanche hazard today will be the formation of new wind slabs.  Wind speeds of 40-50 mph are occurring in Valdez and Thompson Pass with gusts to 70 on Thompson Pass.  New snow is forecasted for Thompson Pass, which will add to the problem.  It is unclear whether this is happening, as all weather stations are showing a decrease in snow heights as of 5:30 am.

    Yesterday there was 2 feet or more of dry settled storm snow above 3000 feet that will be redistributed into stiff wind slabs on lee aspects.  Expect these wind slabs to be reactive up to 3+ feet in depth above 3000 feet.

    Below 3000 feet a rain crust that formed on 12/1 may prevent the wind from eroding the snowpack below that level, limiting the depth of wind slabs to 1-2 feet.  This rain crust will act as a smooth sliding surface on lee slopes where new wind slabs are formed.

    Wind slab hazard will be hard to miss today as the mechanism will be very apparent.  Avoid terrain traps and travel in gullies.  Shooting cracks will be a sign of instability that indicate you should avoid slopes steeper than 30°.

  • Persistent Slabs

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

    Our thin early season snowpack has a couple layers of concern in the mid snowpack and lower snowpack.  The reactivity and presence of these layers has varied significantly with location and elevation making predicting the potential for them to act as failure planes challenging.

    What we do know:  

    • Snowfall and rain at low elevations has been fairly consistent from 11/26 to now.
    • This load of new moisture has been putting stress on a thin snowpack
    • wind slab formation will continue to put stress on a relatively weak snowpack.

    What we don't know:

    • What does the snowpack look like above 5000'?
    • Are there areas where the 11/26 interface (day clear weather turned to stormy) continues to harbor surface hoar?
    • What is the structure of the Maritime snowpack

    Stress is being added to potential persistent weak layers on lee aspects, while windward slopes are being stripped of their load.  Smaller avalanches may be able to step down to layers deeper in the snowpack, creating larger slab avalanches.  Stability test results and snowpack structure have varied significantly from place to place over the last two weeks, creating high uncertainty about this avalanche problem.

     

Avalanche Discussion

The weather pattern has officially changed from warm and wet to cold and windy.  Wind slabs will be reactive today as there is 2 feet+ of dry snow available for transport.  Wind slabs are the most reactive as they form and soon after making today especially dangerous.  Human triggered avalanches are likely and lee slopes that receive significant loading may see natural avalanche activity failing in the mid and potentially lower snowpack.  Expect for the depth of the snowpack to be significantly eroded above 3000' over the coming days as very strong North winds are expected.  Below 3000' may be spared to some extent due to a rain crust in place, but there is not much snow at those elevations to begin with.

There is quite a bit of uncertainty when it comes to the distribution and reactivity of persistent weak layers.  In some areas stability tests have produced concerning results along with poor snowpack structure.  In other areas, the snowpack is looking healthier with no concerning stability results.  Currently it appears that areas below brushline where the snowpack is thinner is harboring weaker faceted snow.  Above brush line, thicker snowpacks have been found with less in the way of stability concerns.  The pattern though, is likely not that simple.   Early season spatial variability creates areas in the snowpack that are thinner with weaker snow that can act as trigger points. 

 

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