Bollettino valanghe

Maritime

Valdez Avalanche Center
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Pericolo valanghe

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

The avalanche hazard is Considerable above 3000 feet and Moderate below.  New  snow over the last 24 hours continues to add stress to the upper snowpack.  Human triggered avalanches are likely above 3000 feet up to 2 feet in depth in specific areas where the wind has redistributed snow into deeper and more sensitive slabs.  Wet loose avalanche activity will be possible both natural and human triggered. 

Problemi valanghivi

  • Wind Slabs

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

    Wind slab avalanches continue to be a concern as 6 inches of low density snow along with light to moderate winds were recorded at Thompson Pass over the last 24 hours.  New snow will mask the visual texture of wind slabs making them more difficult to identify. Fresh wind slabs may have formed in wind-channeled terrain.   Expect to find areas of sensitive snow below ridge lines and on steep terrain.  Stability has been observed and reported as good at mid elevations of Thompson Pass, these conditions are expected to continue as the new/old interface is expected to bond well and a deep and stable snowpack is currently in place at mid elevations.  Instabilities are expected at upper elevations as storm totals will be higher and the effect of wind redistribution is greater.  It will also be possible to encounter unstable snow in convex or unsupported terrain at upper elevations as new snow instabilities are possible. 

    Use caution at upper elevations as continued snowfall will keep instabilities in the upper snowpack a concern in steep wind loaded or steep unsupported terrain.

  • Loose Wet

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    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.   Expect all aspects to be affected at low elevations today.  At mid to upper elevations wet loose activity may be limited due to cloud cover.  A clearing trend today may allow for south and west aspects to become reactive later in the day.

    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.   Roller balls and snow snails are a good visual indicator that wet loose is currently an issue.  Plan your route to avoid exposure to steep low elevation slope when the surface is not frozen.

    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

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    2.5–3

     A persistent weak layer consisting of buried surface hoar 2-4 feet beneath the surface exists in our snowpack above 3000'.  This layer has not been observed or reported to be reactive along the road corridor near Thompson Pass in the most commonly used areas.  Large human triggered avalanches have occurred in more protected areas beyond the road corridor where higher snowfall totals have occurred, and the layer in question likely formed more substantially and was buried more intact.  The last avalanche activity reported at this layer occurred on 3/2 with one instance involving a D2-2.5 avalanche that caught and carried a skier causing him to pull his airbag and lose some gear.  It is very likely that other avalanches have been triggered at this layer since and have not been reported.

    This layer has been observed in multiple locations above 3000' and has been observed to be rounding (gaining strength) and also mixed with other grains.   This is positive progress, however, we need to keep in mind that incremental loading of this layer can increase its sensitivity.  Storm slab avalanches may have enough force to step down to this weak layer.  Assesment of this layer will be challenging as it can be difficult to locate and ECT tests will be less effective as this layer becomes deeper with continued snowfall accumulation.  Propagation Saw Tests will be a more effective tool to test this layer.

     

    Propagation Saw Test (PST) in the Tsaina valley 4200' that was reactive on 3/29 BSH. PST END 30/100 down 95 cm.  

    Photo: Gareth Brown

Avalanche Discussion

RECENT AVALANCHE ACTIVITY:  

Observations have been limited over the last 48 hours due to cloud cover preventing travel into the alpine.  

Last human triggered activity at 3/29 layer was reported on 3/2

DISCUSSION:

Human triggered avalanches were reported at upper elevations during the last clear weather on 4/10.  A continuation of strong south winds and incremental snowfall will lead to a continuation of unstable conditions at upper elevations.  Mid elevations where storm totals are lower and temperatures have been warmer have promoted better stability. These conditions are expected to continue in these areas.  Instabilities exist in specific areas.  You can lower your exposure to avalanche hazard by avoiding steep terrain near ridge lines and low elevations where wet loose avalanches may be a concern.

We continue to be monitoring the 3/29 BSH layer.  Before the most recent snowfall, metamorphism has been observed in multiple locations with rounded buried surface hoar grains being observed.  Before the most recent snow, the chances of triggering an avalanche at this layer were unlikely.  The likelihood of affecting this layer has once again moved to possible due to the uncertainty regarding how the additional stress of new snowfall will affect this layer's sensitivity.  We are moving towards removing this layer from the problem list, however are waiting to see if continued snowfall allows this layer to reactivate.

 

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: 286  inches

Valdez April snowfall: 11 inches

Valdez height of snowpack: 69 inches

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

46 mile height of snowpack: 66 inches

 

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