Bollettino valanghe

Continental

Valdez Avalanche Center
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Pericolo valanghe

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

The avalanche hazard is HIGH above 4000 feet and Considerable below.  Above 4000' travel in avalanche terrain is not recommended.  Human triggered avalanches up to 3 feet in depth are very likely and natural avalanches are likely.

Avalanche forecasts are issued Wednesday- Sunday.  The next forecast will be published 4/3.  In the meantime expect the avalanche hazard to remain elevated, with human triggered avalanches likely up to 3 feet in depth.

 

Problemi valanghivi

  • Storm Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Very Likely
    Dimensione
    2–3

    The upper snowpack is receiving a significant load of new snowfall along with strong southerly winds.  Thompson Pass DOT estimated 12-16 inches of storm total as of 6 am at road level with an additional 12+ inches possible by Monday evening.   Snowfall totals at upper elevation likely exceed 2 feet.  This amount of snowfall would create Considerable hazard on its own, however this new snow is being deposited on a layer of surface hoar that formed 3/27.  This layer has been reported and observed as being widespread above 4000'.  

    Surface hoar is a type of snow grain that is notorious for acting as a weak layer that has the potential to stay reactive for prolonged periods.  Confidence is high today that it will be very likely for a person to trigger an avalanche above 4000'.  Travel in avalanche terrain is not recommended today at upper elevations.  Below 4000' where surface hoar may not exist storm slab avalanches will still be likely as strong winds and heavy snowfall have created a high likelihood for unstable snow to exist on slopes steeper than 30°.

    If you attempt to travel in the mountains today, very conservative terrain choices are recommended.  Avoid traveling on large connected slopes as natural avalanches are likely today at upper elevations and remote triggers will be possible.

     

    (3/28/2024)

    2-6 mm Surafce Hoar on ridgetops in The Books ~5400'.

    Photo: Gareth Brown

  • Deep Persistent Slabs

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

    The 3/9 layer of buried surface hoar that was previously listed on our avalanche problem list has returned as a concern due to the possibility that significant snow and wind will reactivate this layer in isolated locations where it exists.  This layer is expected to exist at upper elevations on protected north aspects in the continental zone.  This layer is now expected to be 3-4+ feet in depth.  Storm slab human triggered or natural avalanches will have the potential to step down to this layer in isolated locations.  

    There is high uncertainty as to whether this layer is still a concern, but is worth considering due to its potential to create very large destructive avalanches if it were to be initiated.  This layer is unlikely to show signs of instability such as shooting cracks or collapsing due to its depth.  Traveling in areas where this layer may exist is not recommended today.

Avalanche Discussion

RECENT AVALANCHE ACTIVITY:  

No natural or human triggered avalanche activity has been reported or observed in the last 48 hours, although natural avalanches likely occurred overnight at upper elevations.

DISCUSSION:

Significant snowfall and wind has created dangerous avalanche conditions in the short term as the upper snowpack adjusts to its new load.  In areas where new snow is falling on surface hoar (3/29 BSH) expect for storm slabs to become persistent and remain sensitive to human triggers in the short to mid term.  This layer overlies soft snow on north aspects.  On E,S, and W aspects this layer may exist on a melt freeze crust that may act as a more effective bed surface.  Winds were moderate to strong just before the recent snowfall.  This may have destroyed the 3/29 BSH layer in some places making identification of this layer more spotty and confusing in the future.  However, the extent of the winds effect on this layer is unclear.

Where the 3/29 BSH does not exist expect storm slabs to gain strength with sensitivity to human triggers slowly decreasing once we are 24 hours beyond the end of precipitation.  In the meantime dangerous avalanche conditions exist.  Human triggered avalanches are likely to very likely at all elevations up to 3 feet in depth.

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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