Bollettino valanghe

Maritime

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Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
2 · Moderato
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In sintesi

The avalanche hazard is Moderate at all elevations.  Human triggered avalanches remain 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 continue to be the main avalanche concern today.  A few inches of new snow is expected to accumulate that will act as additional ammunition for wind slab developement in specific areas.  This will likely be the last day that wind slab is our main concern, as storms begin to roll in and the focus will shift to new snowfall.

    Northeast wind had a slight increase in strength overnight across all weather stations.  Winds are forecasted to slowly abate by this afternoon, but with additional snowfall, the wind that remains will fuel additional windslab development in specific areas.  On 1/3 wind loaded pockets on the lee side of terrain features were found to be reactive with long shooting cracks in isolated areas of Girls Mountain south aspect.

     Wind slabs now exist 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 of terrain features (lee), to 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 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.

     

     

    (1/3/2025)

    Shooting cracks on a windloaded slope of lower Girls Mountain

    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 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 crust 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, it 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:

Wind slabs have been forming over the last 2 days as Northeast wind increased along high elevation and wind channeled terrain.  Wind slab pockets  were observed as being reactive on 1/3.  With continued wind today and a couple inches of new snow accumulation, it is expected that it will remain possible to trigger a wind slab avalanche in specific terrain up to 2 feet in depth today.  The focus of avalanche problems will be shifting over the next 24-36 hours as old wind slabs become stubborn to triggers and storms bring moisture from the Gulf of Alaska that will produce rain at lower elevations and heavy snow at upper elevations.  

Our focus moving forward will concentrate on how much snow is expected to arrive?  What the freezing level will be? And lastly, what layers in the snowpack will this new snow be putting stress on, and how will they react?

As is typical with pattern changes, snowfall amounts are unclear, but 1.5-2" of water is expected over the next 48 hours.  This could translate into nearly 2 feet of new snow at upper elevations.  Freezing line has the potential to rise up to 2500 by Sunday evening.  If this does occur, could result in a more than 60° temperature swing for some areas in a 3 day period.

New snowfall will be falling on old wind slabs in wind channeled terrain, old wind pressed powder in some areas, and significant surface hoar in wind protected areas below 3000'.

Beneath the surface the 12/22 layer of BSH that has been unreactive should continue to be monitored as an increase in stress from new snowfall could increase it's sensitivity.

A rain crust sandwich from early December, with facets in the middle  exists below 3500'.  This crust facet combo is concerning setup when it is examined on its own without putting into context where it exists.  The elevation band where this layer is the most sensitive is also where there is thick exposed alders currently.  It is expected for sensitivity to increase at this layer with new snowfall in isolated terrain.  This would include steep, vegetaion free slopes below 3000'.  The Buttresses of Nicks through Cracked Ice could be one of these areas, as well as steep slopes above river canyons.

Surface Hoar that formed during the last 6 days of clear weather is significant in places, however the recent uptick in wind has destroyed it in many locations above 3000'.  It is also possible if the freezing line actually does rise to 2500' that rain will eliminate this layer where it was most pronounced.

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- 1/4 24 hour Snow Water Equivalent Inches Height of Snow January Snowfall Season Total Snowfall Valdez     0    0    17     0     35 Thompson Pass    0    0   N/O    0    N/O Nicks    0    0    50    0 N/O 46 Mile    0     0   22    0 N/O

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