Lawinenlagebericht

Maritime

Valdez Avalanche Center
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Lawinengefahr

Hochgebirge
2 · Mässig
Waldgrenze
2 · Mässig
Unterhalb
2 · Mässig
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Kernpunkte

The avalanche hazard is Moderate at all elevations.  Human triggered avalanches are possible in wind affected areas.  Wind slab avalanches will have the possibility to step down to layers deeper in the snowpack on larger slopes, creating higher consequence avalanches.  Natural avalanches are unlikely.

Lawinenprobleme

  • Wind Slabs

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

    Over the last 4 days of clear weather, winds have been uncharacteristically light for this time of year.  Some wind slab development did occur towards the beginning of the cycle in terrain that is close to the wind funnel of the Thompson Pass Gap.  These older wind slabs have been found to be gaining strength and are stubborn to unreactive to triggers.  Buried surface hoar remains a concern a little over a foot below the surface, however, the areas that have seen recent wind slab development will also be the areas where it was most likely for surface hoar to be destroyed prior to being buried by pre storm wind.

    Pressure gradients are expected to tighten today, which will lead to an increase in strength and distribution of North /Northeast wind.  At 5:30 am, wx stations were still only showing light winds at Nicks with a slight uptick in wind speeds on Thompson Pass.  If winds do become more widespread expect to encounter areas of fresh wind slab development.  The first areas for these to form will be the lee side of high elevation ridgelines and cross loaded gullies.  Pay attention to the strength and direction of the wind in the area you travel and what slopes could be loaded.  Using test slopes without consequence is a good way to keep an eye on the sensitivity of the surface snow.  Wind slabs may be deposited on surface hoar that was at the surface yesterday making new wind slabs more sensitive in some locations.  Pay attention to the surface snow, as it will give clues about wind direction. Wind slabs can have a smooth pillowed appearance or a rippled texture.

    A surface wind slab will have the potential to step down to deeper layers in the snowpack (see problem 2) on larger slopes.

     

     

    Example of a visual clue:

    The eroded face of the snow surface points toward the previous or current wind direction.

    Photo: Gareth Brown

  • Persistent Slabs

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

    There is a layer of buried surface hoar from 12/22 that can be found abouut 16 inches below the surface of the snow in low, mid and in some places upper elevations.  Over the last few days observations have found this layer is being absorbed to some extent by the soft snow beneath.  This is making this weak layer more challenging to identify and when exposed it has been found to be mixed with other grain types.  This lowers the likelihood of human triggered avalanches to be initiated on this layer where this process is occurring.  Stability tests continue to show no propagation with ECTN scores of 18-25.  The concern is that there is a clean shear at this interface and there is uncertatainty about its spatial variability.  

    Even though a handful of observations have been pointing to this layer being less of a concern it will be important to continue to look for and test the sensitivity of this layer.  Buried surface hoar is notorious for remaining weak for long periods of time and catching even the most experienced users off guard.

    Shallower wind slab avalanches will have the potential to exert enough force on the snowpack to cause step down avalanches at this layer.

    (12/26/2024)

    12/22 BSH at 3800' crud

    Photo: Gareth Brown

Avalanche Discussion

Observed Avalanche Activity last 72 hours: 

NONE

Forecast Discussion:

There is quite a bit going on in our snowpack right now, with a high degree of spatial variability.  This variability, combined with multiple layers in our snowpack will make it possible for conditions to vary from the forecast in the area you choose to travel.  Use this avalanche product as a guide to assist in your own assessment depending upon where you go.

Winds are forecasted to increase today, making fresh wind slab formation the most likely problem to encounter.  Areas that are more commonly wind affected, like those near Thompson Pass have less snow available for transport as some degree of wind redistribution has already occurred.  Areas previously unaffected by wind will likely be the places that have a higher sensitivity today if active wind loading is occurring.

As you look beneath the surface there are three layers that should be monitored by users.

The first and most currently relevant is the 12/22 layer of Buried surface hoar.  A decent amount of natural avalanche activity occurred on 12/28 that is assumed to be attributed with this layer.  This layer was initially very pronounced in snow pits and has been gradually deforming and in the process of being absorbed by the snow beneath.  Even though test results have been pointing towards a lower likelihood of human triggered involvement, this layer remains guilty until proven innocent due to the grain type and the slab above.

Second is a rain crust sandwich with melt forms in the middle that are in the process of faceting.  These rain crusts are from 12/10 and 12/5 and both are showing signs of losing strength.  These crusts go up to 3500' and gradually taper away and dissapear as you gain in elevation.  This layer is not expected to be a current concern as far as human triggered avalanches because the upper crust still maintains some strength and the slab above is thought to be insufficient to overload this layer.  The caveat to this would be that an avalanche that intiates at an upper layer could produce enough force to step down to this layer.  As this layer continues to lose strength and the load above increases, the sensitivity of this layer may increase.

Lastly is the Wind affected snow that formed in Mid-late November.  This layer has been found to be extremely variable.  It is generally a meter deep in the snowpack with some degree of facets beneath.  The variability lies in the strength and thickness of this layer.  As recently as 12/31 this layer was found close to Thompson Pass to be 20 cms thick and very difficult to shovel through.  In other areas it has been found to be only 5 cms thick and 1 finger hard.  This is another layer that could be a concern in the future, step down avalanches are possible.

Looking into the future fresh surface hoar formation has been noted up to ridgelines.  An increase in winds today and tomorrow will remove this layer on windward slopes.  This will be our next most relevant layer of concern once new snowfall arrives.  Tracking its distribution while it is still on the surface will be important to understand where future instabilities may lie.

Additional Information:

Continue to avoid Glide cracks in the area where they exist from Nick's Buttress through Cracked Ice at mid elevation.  Some of these are being filled in by snow and no recent activity has been noted

If you travel in the Continental zone today, exercise extra caution as there is very limited field data from this location.  It is unclear as to whether deep slab instabilities exist, however it is a possibility.

If you get out in the mountains today consider leaving an observation to help increase the understanding of current snowpack stability.  

A weather and snowpack season history is available by clicking on the Weather History tab that is located above the bottom line statement once you have entered the full forecast.

Season Snowfall Data

Location 24 hour Snowfall Inches- 1/2 24 hour Snow Water Equivalent Inches Height of Snow January Snowfall Season Total Snowfall Valdez     0 N/O    17     0     35 Thompson Pass    0 N/O   N/O    0    N/O Nicks    0 N/O    50    0 N/O 46 Mile    0   N/O   22    0 N/O

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