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 less than 1 foot are the most likely problem to encounter at 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 possible.

Avalanche problems

  • Wind Slabs

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

    Expect shallow wind slabs to exist on multiple aspects at upper elevations.  On 4/3 SE winds kicked up and were beginning to form shallow pockets of wind slab that were reported to be sensitive to triggers below ridge lines in some locations.  These have likely gained strength but may remain reactive in isolated locations.  New snowfall will mask the texture of these older slabs making them more difficult to visually identify.

    During the day and night of the 4th, our area received 2-6+ inches of new snow depending upon the elevation and location.  This new snow was found to be fairly dry and sensitive above 3000 feet on shaded aspects on the 5th.  This new snow will have formed shallow wind slabs up to 1 foot in depth due to an increase in north winds yesterday that became moderate during the day.  If the weather allows you to get up high today watch for pockets of wind loaded new snow below ridgetops and in cross loaded gullies,  these may have a pillowed appearance or a rippled texture and are expected to be sensitive to triggers in the short term in specific locations.  

    Winds are expected to once again shift during the day to SE.  Expect to find new and old wind slabs on a variety of aspects at upper elevations.

    Wind stiffened snow may increase the likelihood of triggering a persistent slab avalanche (problem 2) and may propagate beyond wind affected snow.

  • 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 yesterday 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 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, we could see the sensitivity of this layer increase in the future.  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
    Possible
    Size
    1–2

    Wet loose avalanches will be possible at low elevations.  Temperatures remained above freezing overnight at low lying elevations on the south side of Thompson Pass.  This will allow for wet loose activity to continue today, especially if the sun can poke out at any point.  

    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 differnt 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.  Roller balls and snow snails are a good visual indicator that wet loose is currently and 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 natural dry loose avalanches were reported in the Dimond area in the last 24 hours.  Other than that no human triggered 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.  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 a clearly 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.  

Try to keep in mind that this scenario can change.  The 3/29 BSH layer has the potential to become active with additional loading of snowfall that is forecasted over the next week.  

 

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

 

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