Bollettino valanghe

Maritime

Valdez Avalanche Center
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Pericolo valanghe

Alta quota
3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
2 · Moderato
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Non aggiornato — questo bollettino è scaduto 3 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

The avalanche hazard is Considerable above 1500 feet and moderate below.  Unstable snow exists on slopes that have been loaded by wind in the last 36 hours.  Human triggered avalanches up to 3 feet in depth are likey on wind loaded slopes and natural avalanches are possible.

Problemi valanghivi

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    1–2

    Winds out of the north began on 1/9 and became strong along ridge tops and wind channeled terrain.  This wind has built slabs in specific areas that were found to be sensitive to human and machine triggers.  These wind slabs are forming on top of faceted snow that may allow wind slabs to propagate further once intiated and to remain sensitive for longer than what is typical.

    New snowfall amounts on 1/7 were ~ 6 inches in the upper elevations of the intermountain and continental zone with about double that in the Maritime zone.  Valdez also received 6 inches on 1/4 with Thompson Pass being mostly skipped.  These differences in snowfall totals will make a big difference in the depth of wind slabs that can form.  On 1/9 sensitive test slopes in the Maritime zone were producing failure up to 3 feet in depth while north of Thompson Pass fresh slabs were reported to be ~ 1 foot in depth.

    Watch for signs of wind loading such as fresh cornice development on ridge lines and terrain features.  Avoid cross loaded gullies and slopes steeper than 30° where fresh wind slabs are present.    Signs of instability such as shooting cracks, natural avalanche activity and collapsing will be a bulls eye indicator of unstable snow.

    NE winds are expected to continue today, although they appear to have peaked in intensity yesterday afternoon, and are forecasted to diminish through the day today.  Areas that are experiencing active wind loading will be the most sensitive.

    Test slope failure at Benzene Alley on 1/9.

    Photo: Gareth Brown

  • Glide Cracks

    • Tutte le quote
    Probabilità
    Unlikely
    Dimensione
    2.5–3

     Glide avalanches are a strange beast that act differntly than other avalanche problems.  Full depth failure can occur independent of snowpack stability.  Or in other words, they can release even when a stable snowpack is in place.

    Since it is not possible to time their sensitivity the only way to mitigate this hazard is by avoidance.  First identify where glide cracks exist and avoid spending time beneath them.  Glide cracks are easy to identify.  They look like crevasses, but exist in non glaciated terrain.

    These do not produce small avalanches,  but rather failure will include the entire snowpack.  

    Glide release on Town mountain

    Photo: Rich Lofton

Avalanche Discussion

Today there will be a high degree of spatial variability regarding stability throughout our forecast area.  Wind slabs that have formed over faceted snow will be the big concern of the day.  The Maritime zone will have much deeper wind slabs than intermountain and continental due to there being a lot more dry snow available for transport.  Expect these wind slabs to be sensitive to human triggers today up to 3 feet in depth depending upon location.

In areas that were protected from the most recent outflow stability will be better.  This is especially true in the intermountain and continental zone where there currently is an insufficient load of new snow atop the 1/7 facets to make them reactive, except for maybe in small pockets of extreme terrain.  In the Maritime zone where snowfall totals were higher there is more stress on faceted snow, although facet development was less significant in this zone and the surface snow in protected areas does not yet have slab character (uncohesive).  Judging slab charcter can be tricky as a small amount of wind or settlement over time can create slabs stiff enough to make a weak layer reactive.  Pay attention to the depth and stiffness of surface snow, seek out wind sheltered terrain where better stability and riding conditions will be present.

Cautious route finding and conservative terrain choices will be essential for safe travel in avalanche terrain today.

Glide cracks have been observed in all three forecast zones.  Avoid travelling beneath these as full depth avalanches can release unexpectedly.

Valdez season snowfall: 160 inches

Valdez January snowfall: 15 inches

Valdez height of snowpack: 62 inches

Thompson Pass snowfall data is currently unavalable

46 mile height of snowpack: 65 inches

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