Avalanche forecast

Continental

Valdez Avalanche Center
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Avalanche danger

Sat
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
2 · Moderate
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Highlights

Backcountry travelers should expect considerable avalanche danger today due to continued windslab formation. Human-triggered avalanches on freshly loaded slopes will increase in likelihood today as new snow is transported by wind. Natural avalanches will be possible in specific locations.

Avalanche problems

  • Wind Slabs

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

    The most likely avalanche problem you will encounter today is windslab. Strong North East winds have been steadily transporting snow for the last several days. Thompson Pass has been receiving light snowfall since 8 pm last night which will add to the amount of snow available for transport and windslab formation. Today you can expect to find wind slabs that vary in age, thickness, and sensitivity throughout our forecast zone. Newer and softer slabs formed from the current snowfall in Thompson Pass will be most sensitive today and could step down into older more stubborn slab layers. Protected areas with lighter winds will be the most likely spots to trigger a D1-D2 windslab today. Exposed ridgetops and other areas with strong winds will have stripped surfaces and/or old stubborn hard slabs.  When encountering wind slabs, always note their extent and thickness when considering their potential hazard. 

    Lower elevations will have a moderate hazard today since less snow is available for transport and slab formation. 

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely
    Size
    1.5–3

    Heavy snowfall and Southerly storm winds loaded our snowpack causing a widespread avalanche cycle on 2/22.  Several storm slab avalanches released on a layer of surface hoar that was buried on 2-17.  Before the storm, surface hoar was observed in isolated areas from Valdez Through Thompson Pass and to the North on the Richarson Highway. This persistent weak layer may still exist in specific wind-protected basins and is expected to be buried around 2 feet deep.  There is currently high uncertainty regarding the extent of this layer and its sensitivity. Avalanches that released on this layer occurred naturally during or immediately after our last storm. No human triggers have been reported at this time.

    Currently, strong winds are creating a hard snow surface that is expected to bridge this deeper layer making it less likely to be affected by a person or other trigger. 

     

    Natural avalanche 2/22 North Three Pigs

    Photo: Gareth Brown

  • Deep Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely
    Size
    2.5–3.5

    The Natural Deep slab that released on Tones Temple on 2/24 has raised questions about potential instabilities deep within our snowpack. The weak layer is still unknown but appears to be near the ground. An additional smaller deep slab was observed in rocky terrain off the south side of Girls Mt on 2/27.  These avalanches have been concerning because they occurred several days after the last avalanche cycle.  There is quite a bit of uncertainty regarding the sensitivity of the layers involved in these large avalanches but we can expect that they would not be triggered directly by a human. A cornice fall or slab avalanche could possibly step down to these deeper layers. 

    Due to the depth of this problem, assessment is near impossible. This avalanche problem is not associated with any signs of stability. Additionally, standard snowpack assessment strategies are not possible with layers this deep.

    The big question is whether or not we will see any additional failures on this deep layer.  Future snowfall that provides a heavy load may be a good test of this situation.  In the meantime minimizing exposure to steep rocky especially on or near wide continuous slopes is advised.  

    Tones Temple deep natural 2/24. Intiated from D1 natural wind slab

    Photo: Gareth Brown

Avalanche Discussion

For today and the rest of the weekend, we will expect cold and windy conditions.  Wind slabs will remain the most likely problem for travelers to encounter but will likely decrease in sensitivity as snow becomes wind-hardened and stripped in areas over the next day or two. As snow available for transport decreases over the next few days, new windslab formation will become limited. 

For the last several weeks avalanche problems have been transient and limited to the top 2-3 feet of our snowpack. This changed dramatically after our last big storm. Several large natural avalanches released on layers deep within the snowpack. Due to the depth of these layers assessment is difficult to impossible We have a high amount of uncertainty regarding the characteristics of these deep slabs at the moment. Deep slabs create a low probability high consequence scenario. Unfortunately, these avalanches give no clues to their existence and are unsurvivable.

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