Bollettino valanghe

Continental

Valdez Avalanche Center
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Pericolo valanghe

Alta quota
3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
3 · Marcato
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In sintesi

The avalanche hazard remains CONSIDERABLE at all elevations. Strong winds will continue to move dry snow, forming wind slabs up to 3 feet in depth.  Human triggered avalanches are likely and natural avalanches are possible.

In addition to avalanche hazard, the risk of frostbite will be HIGH today on Thompson Pass.

Avalanche Forecasts will be issued 3 days/week during December.  The next forecast will be issued Friday December 12th.  5 day/week forecasts will return in January once 2026 funding comes through.

Problemi valanghivi

  • Wind Slabs

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

    The situation has not changed much from yesterday.  Wind slabs will continue to be the main hazard with human triggered avalanches likely 1-3+ feet in depth on lee aspects, and cross loaded slopes and gullies.  

    What has changed will be the hardness of the windslabs and their sensitivity.  Expect for windslabs to now be pencil hard and have a hollow drum-like feel especially near Thompson Pass.  Sensitivity may be lower than it was yesterday, however, wind slabs that are triggered will propagate further.  Consider the consequences of the slope you are travelling on failing.  Is there a terrain trap or exposed rocks below?  How big is the slope, and what is the potential?  Windward slopes will be safer for travel today.

    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.

     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

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    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.
    • Stability tests have been variable from place to place

    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

Avalanche activity in the last 72 hours:  None observed

Forecast Discussion:  Today is the second full day of near hurricane force winds on Thompson Pass.  Snow available for transport will be significantly less today, although winds continue to increase which causes further gouging of the snowpack.  Expect to find much stiffer wind slabs today that will have a hollow drum-like feel.  These stiffer slabs will have the potential to fail behind you once you are on a slope and propagate wider than softer slabs that existed yesterday.

The strength of wind that we are receiving tend to cause more sublimation ( snow goes from a solid to a gas) rather than deposition.  Areas that are receiving lower wind speeds (20-30mph) may actually be more dangerous than Thompson Pass as a greater percentage of the redistributed snow will form windslabs rather than sublimate into the atmosphere.  Pay attention to the depth and sensitivity of new windslabs and avoid slopes of consequence until new slabs are given enough time to stiffen and gain strength.  

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 fewer 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. 

Additional Details:  There is no field data from the Maritime zone due to low snow coverage and thick brush restricting access.  Numerous Glide avalanches have released in the Maritime zone in the mid elevation band.  Some of these may have failed without previous visible glide cracks.  Avoid travel below glide cracks as they can fail at any time.  Their likelihood of failure is independent of the snowpack stability.

 

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