Bollettino valanghe

Maritime

Valdez Avalanche Center
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Limite del bosco
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In sintesi

The avalanche hazard is Moderate at all elevations.  Human triggered avalanches are possible up to 2 feet in depth in wind loaded areas.  Smaller human triggered avalanches may be able to step down to deeper layers in the snowpack in the Continental zone creater larger, more destructive avalanches.  Natural avalanches are unlikely.

Problemi valanghivi

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–2

    Wind loaded snow will be the main avalanche concern today.  Northeast wind increased in strength and distribution on 1/2.  High elevation flagging was observed, indicating wind slabs are forming in specific areas, these will be possible for a person or machine to trigger an avalanche up to 2 feet in depth.  The best way to avoid this avalanche problem will be to first recognize where it may exist.  Surface snow will give visual indicators as to which direction the wind is blowing. Ex: freshly formed wind lips on terrain features point towards wind loaded slopes. Wind slabs will form on the opposite side (lee) of the direction of the wind.  The most likely places to find wind slabs will be: cross loaded terrain, lee side of terrain features, and lee of high elevation ridges.  The strength of wind may form slabs further down the slope from high elevation ridges than you may expect.  Wind slabs will have a hollow drum like feel where they are over a day old and may feel like an upside down storm slab where they are freshly formed.  Signs of instability such as shooting cracks and collapsing are direct indicators that a person or machine can trigger wind slabs.

    Better riding quality and stability will be found in areas that are unaffected by wind.  

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

     

     

    (1/2/2025)

    Upper elevation flagging

    Photo: Gareth Brown

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Unlikely
    Dimensione
    1.5–2.5

    There is a layer of buried surface hoar from 12/22 that can be found about 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.  This layer remains on our list because buried surface hoar is notorious for remaining weak for long periods of time and catching even the most experienced users off guard.  However, test results have been very consistent indicating this layer is not reactive.  

    Below the surface hoar is a rain crust sandwich with factes in between.  These crusts extend up to 3000-3500'.  Below 2000' the upper crust is still supportive and is not a current concern.  Between 2000' and where the crust goes away, the upper cust has lost enough strength to become a weak layer.  Collapsing has been observed with failure on small steep slopes that occurs in the factes between the crusts, with the snow above acting as a slab.  This is a persistent avalanche problem, however is only a concern in very specific terrain due to the elevation band where it exists.  Most areas where this layer is reactive there are thick alders that act as anchors and prevent a continous slab from forming.  This layer could be a concern above terrain traps, and steep open slopes without vegetation below 3000'.

     

    (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.

Wind slabs continue to be the main concern today.  In addition to wind slabs, frostbite will be another hazard. Windchill values of -50 are forecasted for Thompson Pass today.  Pay attention to the amount of wind redistribution that has occurred in the area you choose to travel and test the depth and sensitivity of wind slabs that have formed.

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.  The upper crust has now lost enough strength above 2000' and is acting as a persistent weak layer.  Thick brush at this elevation prevents this layer from being much of a concern in the majority of areas.  Steep slopes free of vegetation below 3000' are a concern.

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 propagation at the ground on an ECT was observed in a snow pit as recently as 1/2.

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- 1/3 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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