Avalanche forecast

Continental

Valdez Avalanche Center
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Avalanche danger

Alpine
2 · Moderate
Treeline
2 · Moderate
Below
2 · Moderate
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Highlights

The avalanche hazard is Moderate at all elevations.  Human triggered avalanches are possible in specific areas 1-3+ feet in depth above 3000 feet.  Below 3000' small natural or human triggered wet loose avalanches will be possible.

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2–3

    A layer of surface hoar (3/29 BSH) is buried under the storm snow that arrived Easter weekend.  The sensitivity of this layer on the Thompson Pass road corridor is low, with lots of slope testers and no observable human triggered avalanche activity.  Sensitivity of this layer is expected to be higher in areas with higher storm totals in protected terrain away from the road corridor.  Human and machine triggered avalanches are possible 1-3 feet in depth.

    Good stability that was observed in many areas close to Thompson Pass may differ in areas with higher new snow amounts or in areas where the new snow has gotten stiffer due to wind redistribution or temperature effect.  We currently have a challenging situation where a persistent (weak) layer exists that is not showing signs of instability in many places even though large human triggered avalanche have been reported.  This setup makes assessment very challenging as stability may be good in close proximity to unstable slopes.

    The density of the slab and its depth will play a big role in the likelihood of affecting this avalanche problem.  Realize that areas that have more than 12 inches of new snow from the last storm will be more sensitive.  Wind stiffened slabs may carry a higher sensitivity as well.  Light snowfall will arive this afternoon at upper elevations .  Only a couple inches of snow are expected during the day today.  This will add some weight to storm slabs, but is not expected to be enough to effect stability during the day.

     

    (4/1/2024)

    3/29 BSH down 16 inches at 4500' on crudbusters

    Photo: Gareth Brown

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–2

    Shallow wind slabs have been observed along high elevation ridgetops formed by moderate south east winds.  This avalanche problem has only been observed at upper elevations so far, but may exist in the mid elevations in wind channeled terrain.  Wind slabs are currently pockety in nature and are yet to form large continous slabs.  The sensitivity of these slabs has been so far been observed to be stubborn, however human triggered avalanches may still be possible in specific areas.  

    Wind stiffened snow may increase the likelihood of triggering a persistent slab avalanche (problem 1) and may propagate beyond wind affected snow.

  • Loose Wet

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–2

    Wet loose avalanches will be possible at low elevations.  Light snowfall may transition to rain at low elevations along the coast.   Cloud cover may limit the potential for this problem above 2000'.  Avoid steep low elevation terrain once more than a a few inches of the surface becomes moist.

    Natural D2 wet loose on solar aspect of Hippie Ridge

    Photo: Gareth Brown

Avalanche Discussion

RECENT AVALANCHE ACTIVITY:  

Several large (D2-3)  human triggered and natural avalanches have been reported in the last 48 hours that failed on buried surface hoar.  Multiple D2-3 natural avalanches have been observed that likely failed last weekend during the last storm including one deeper crown of 3+ feet in the Tonsina on Japanese Wall.  Several wet loose up to size 2 have been observed on steep solar aspects as well.

DISCUSSION:

The latest storm deposited 4-24+" of new snow depending upon elevation and proximity to the coast.  This new snow fell on a layer of surface hoar that is fairly widespread on the northerly half of the compass above 3000'.  After a couple of days of mostly clear weather, more has been learned about this layer of buried surface hoar (3/29 BSH).  The sensitivity of this layer has been observed to be low in areas with less than 12" of settled storm snow.  This includes the Thompson Pass road corridor where lots of slope testers have been out without any observable human triggered avalanches.  Many of these tracks were in the mid elevations where storm totals are lower.  Be aware that stability can differ depending upon the depth of new snow.  Human triggered avalanches remain possible 1-3+ feet deep, especially in areas where storm totals exceed 16" and/or the slab has been stiffened by wind or temperature.  Buried surface hoar is notorious for catching people off guard and has the potential to fail even after many tracks have been laid down on a slope.  If you can identify this layer in a snowpit assume that human triggered avalanches are possible even if stability tests provide negative results.  Continue to look for this layer in snowpits and pay attention to settled storm snow depths and cohesion.

New snowfall through the week will be adding stress to this potential weak layer and may increase its sensitivity with time.  Winds have been moderate to light, however small shallow wind slabs may be encountered below high elevation ridgelines.

Additional Concerns:

This is the time of year when cornices begin to fail.  You can significantly reduce your overall exposure in the mountains this time of year by avoiding traveling on top of or under cornices.

A very significant Glide avalanche/ landslide in Upper Stuart Creek last week is a great reminder of the destructive forces involved with glide crack failure.  Glide cracks exist in isolated areas and will be a hazard throughout the season until they fail.  Avoid exposure to glide cracks.

Valdez season snowfall: 269  inches

Valdez March snowfall: 20 inches

Valdez height of snowpack: 70 inches

Thompson Pass season snowfall: 596 inches as of 3/1

46 mile height of snowpack: 68 inches

 

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