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.  Freshly formed wind slabs up to 1 foot in depth that may be hidden by light snow are the most likely problem to encounter at mid-upper elevations.  The most dangerous problem is weak snow that is buried 1-3+ feet deep above 3000 feet.  At low elevations natural and human triggered wet loose avalanches will be likely.

Public avalanche forecasts are issued Wednesday-Sunday. The next forecast will be produced on 4/10.  

Avalanche problems

  • Wind Slabs

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

    Winds have been moderate at times over the last few days with the overall direction shifting multiple times.   The strength of the wind has been sufficient to form pockets of wind slab near ridgelines and mid elevation wind channeled terrain.  On 4/3 winds were blowing out of the SE, on 4/5  they shifted to the N, and then on 4/6 returned to the SE with light snowfall intermittingly occurring.  This pattern will have formed pockets of wind slabs on multiple aspects.  This strength of winds is not expected to have formed large areas of sensitive snow, however light snowfall yesterday with decreasing winds will likely have masked the visual texture making assessment and avoidance more challenging. Expect wind slabs to exist on multiple aspects at upper elevations up to 1 foot in depth in specific locations. 

    Wind stiffened snow may increase the likelihood of triggering a persistent slab avalanche (problem 2).   Wind slab avalanches may be able to step down beyond wind affected snow and create very large destructive avalanches.

  • Persistent Slabs

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

    A less likely, but far more dangerous avalanche problem is a layer of buried surface hoar (3/29 BSH) that was covered by 12-36" of new snow above 3000' easter weekend.  This weak layer continues to be identified in snow pits above 3000' with low sensitivity in stability tests.  This layer was found in the Tsaina valley on 4/5 at 4000' down 95 cms , however was not located at 2900'.  This aligns with our thinking that this layer only exists above 3000', so our confidence is high on the distribution, as this observation has been repeated in multiple locations.

    Over the last week hundreds of ski tracks were laid down in the Thompson Pass road corridor mostly at mid elevations in popular sled skiing areas.  No significant human triggered avalanche activity was reported or observed in these areas.  Many high elevation north facing peaks on the road corridor are yet to be tested.  A couple significant human triggered and natural avalanches were reported at the 3/29 BSH layer further from the road corridor where BSH was likely more preserved when snow fell and storm totals were higher.  It is also very likely that there were more human triggered involvements with this layer that were simply not reported.

    Even though sensitivity has been low in the most popular areas for travelling, human triggered avalanches remain possible in areas with higher storm totals, steep convex terrain or even small wind slabs that are able to step down to this layer.  In addition, continued light snowfall is incrementally loading this weak layer, sensitivity at this weak layer could be higher today.  Continue to monitor this layer by digging pits and being selective in your terrain choices.

    (4/1/2024)

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

    Photo: Gareth Brown

  • Loose Wet

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

    Wet loose avalanche activity will be likely today.  Fresh snow that has fallen over the last few days will be shedding off steep solar aspects during the heat of the day.  Plan your route to avoid exposure to slopes when they are the most prone.

    Wet loose conditions are easy to identify.  Once more than a few inches of snow becomes moist-wet (you can easily form a snowball) then wet loose avalanches will become possible both human triggered and natural on steep terrain.   Different aspects will experience peak hazard at different times of day.  East aspects are the first to warm up, then South and finally West.  Low elevation slopes that are perpendicular to the sun will be the most prone to wet loose activity, however wet loose activity is expected to extend into the upper elevations today on solar aspects.  Roller balls and snow snails are a good visual indicator that wet loose is currently an issue.  

    Avoid travelling on or below steep terrain where more than a few inches of moist snow exists.

    Natural D2 wet loose on solar aspect of Hippie Ridge

    Photo: Gareth Brown

Avalanche Discussion

RECENT AVALANCHE ACTIVITY:  

A couple of natural dry loose avalanches were reported in the Dimond area in the last 48 hours.  Other than that no human triggered or natural avalanches have been reported in the last 48 hours.

Several large (D2-3)  human triggered and natural avalanches occurred just after the Easter storm 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 most likely avalanche problem for a person to encounter today is newly formed shallow wind slabs near upper elevation ridges that are expected to be up to 1 foot in depth.  This problem may be difficult to assess and avoid due to light snowfall yesterday with decreasing winds that may have masked these slabs making them more difficult to visually identify.  The most dangerous problem a person could encounter is triggering a 1-3+ foot deep persistent slab that fails on buried surface hoar.  In the most popular areas of Thompson Pass, sensitivity at this layer has been low with multiple stability tests producing a range from moderate- hard ECTN's to ECTX's. This is an interesting scenario where we have an identifiable weak layer with a slab above it that is now slowly growing in depth and cohesion with time and continued light snowfall.  On paper this looks like a clearly dangerous set up, however in reality it has so far not been reactive in many places, especially near the road corridor.

 7  days is not enough time to call this problem dead, incremental snowfall has added weight to this potential weak layer over the last few days which may have increased sensitivity in certain locations.

 

 

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: 284  inches

Valdez April snowfall: 5 inches

Valdez height of snowpack: 74 inches

Thompson Pass season snowfall: 698 inches as of 4/5

46 mile height of snowpack: 66 inches

 

Regions covered