Bulletin d’avalanche

Maritime

Valdez Avalanche Center
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Danger d’avalanche

Alpin
3 · Marqué
Limite forestière
3 · Marqué
Sous la limite
1 · Faible
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Périmé — ce bulletin a expiré 7 months ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

The avalanche hazard is Considerable above 1500 feet and low below.  Heavy snowfall is sitting on top of weak snow in some places, making human triggered avalanches likely up to 5 feet in depth.  Simple terrain choices are recommended today.   The hazard is low below 1500' where a rain saturated snowpack has refrozen and gained strength.

Public avalanche forecasts are issued Wednesday-Sunday at 8 am. 

Problèmes avalancheux

  • Storm Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    2–3

    The word of the day is UNCERTAINTY.  The latest round of snow was large enough to significantly change our snowpack.  Numerous large (D3) natural and artillery triggered avalanches have been reported by DOT that occurred during peak intensity of the storm.  Now that the storm has moved on, it is unclear how quickly the snowpack will accept the new load of snow and should warrant caution and conservative terrain choices until more information can be gathered.

    What we do Know:

    • 3+ feet of snow has fallen since the 14th.
    • New snow is falling on a snowpack with facets (weak snow) near the base and mid-pack.
    • Natural avalanche activity has occurred.
    • Temperatures warmed thrugh the storm driving the freezing line up to 2500'

    What we dont know:

    • How well is the new snow bonding to the old wind damaged snow from December?
    • What kind of instabilities exist within the new snow? (Is it top heavy?)
    • To what degree did weak faceted snow become overloaded and fail naturally? Are there places where weak snow is still holding on by its fingernails?

    We should all aim to answer the above questions before attempting to venture into consequential avalanche terrain.  Typical terrain progression should not be relied upon due to the potential presence of a deep persistent weak layer (see problem 2) that may not give feedback even with the presence of unstable snow.  If signs of instability exist, listen to them and back off any exposure to terrain steeper than 30°, whether direct or overhead.  Patience is advised until more information can be gathered.

  • Deep Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    2.5–3.5

    Prior to the most recent storm, we had two layers of concern that we were labeling as persistent weak layers.  The first was the 12/1 rain crust that existed below 3500'.  The second being faceted snow above 3000' at base of the snowpack capped by knife hard wind slabs of varying thickness.  

    The 12/1 rain crust was very sensitive even before the latest storm, and this layer may have been crushed, causing natural avalanches in steeper terrain.  Until this can be confirmed, a conservative and defensive approach to terrain is recommended below 3500'.

    The most important question and the biggest current knowledge gap is what affects did the new snow have on the December facets above 3000'.  Were the knife hard wind slabs above able to support the weight of the new snow? Did naturals occur where facets were the most developed?  Is it possible for a person or machine to affect this weak snow and trigger a hard slab avalanche?  These are the most important questions moving forward and will be the most difficult to answer clearly due to the depth of the weak layer and the associated spatial variability of the December wind slabs, which further complicate the matter.  Signs of instability associated with facets at the base of the snowpack are unlikely to exist due to their depth even in areas where unstable snow exists.  Snowpack assessment of this layer will be challenging even for avalanche professionals.

    Once again, the travel advice for today is conservative terrain choices and patience.

    (12/24/2025)

    Developed facets beneath knife hard wind slab @3200' Crudbusters

    Photo: Gareth Brown

Avalanche Discussion

Avalanche activity in the last 72 hours: Numerous natural and artillery triggered avalanches have been reported by DOT.  So far, overcast skies have prevented a detailed account of avalanche activity.  A more detailed account of the most recent avalanche cycle is coming soon.

Forecast Discussion:

The development of our snowpack this year has been unusual and marked by extremes.  A December with hardly any snowfall, extreme North wind and well below average temperatures left us with a thin, faceted snowpack with a high degree of spatial variablilty.  Strong North wind events that scour the snowpack are no stranger to Thompson Pass, however the duration of the event along with the shallow snowpack to begin with, was unique.  The December arctic blast gave way to near consistent snowfall the first half of January that has climaxed with an atmospheric river delivering 36" of snow and 5" of water to the town of Valdez.  

The agressive transition in weather has very predictably caused a sharp rise in instability.  Now that the weather has mellowed out, the next puzzle piece we are searching for is, how quickly will the stability curve fall.  

 For more information regarding our snowpack, see our Season summary and Observations sections. 

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