Avalanche forecast

Continental

Valdez Avalanche Center
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Avalanche danger

Alpine
2 · Moderate
Treeline
2 · Moderate
Below
1 · Low
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Highlights

The avalanche hazard is Moderate above 2000'.  Human triggered avalanches are possible 1-2 feet in depth on the lee side of ridgelines, terrain features and cross loaded gullies.  Avoid slopes steeper than 32° where the NE wind from yesterday has moved the new snow into deeper and stiffer slabs.  Natural avalanches are unlikely

Avalanche problems

  • Wind Slabs

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

    Human triggered avalanches are possible in specific locations 1-2 feet in depth, this includes areas where the new snow that fell on 12/6 has been redisrtibuted by strong NE wind that accompanied the storm.  Snowfall totals are unclear although 6-12 inches have accumulated in the lower elevations with higher amounts possible with elevation gain.  

    Snowfall rates slowed or stopped overnight which will allow new slabs to settle a bit, although sensitive pockets of wind loaded snow likely remains.  Pay attention to how previous wind has redistributed the new snow and test the sensitivity of freshly formed wind slabs using small test slopes without consequence.  

    Avoiding wind loaded terrain will provide better stabilty and riding conditions today.

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  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1.5–2.5

    New snow and wind has added stress to a potential persistent weak layer that may exist in isolated locations at high elevation in the Continental zone.

    A natural avalanche was observed on 12/1 around 5400' on The Shovel "40.5 mile peak" that had a very wide propagation.  Crown not only included the entire start zone, it wrapped around a rocky terrain feature indicating a persistent layer as the failure plane.  Crown width estimated at 1500' mapped on google earth, depth was difficult to tell but probably in the 1-2 foot range.  A few other naturals were visible on upper ramps of 40.5 mile, although they were not nearly as wide.

    It is possible this weak layer is isolated to high elevation areas (above the Thanksgiving rain crust) in the Continental zone.  This layer may have developed during the clear and cold period just before the Thanksgiving warmup.  It is likely this layer was only  preserved in areas that were sheltered from the strong winds that accompanied the 11/20 cold spell.  A lack of natural activity from other areas would support this idea.  Below 4500' this layer was likely rained away and in wind exposed terrain above 4500' likely destroyed.

    This layer has not been identified in snow pits or reported by others.  Therefore, there is a large amount of uncertainty dealing with distribution and sensitivity of this layer.  More information will need to be gathered.

Avalanche Discussion

Similar to yesterday, the main stability concern  will involve new snow that was redistributed yesterday by moderate to strong NE winds.  Valdez received about 5 inches at sea level and 10 inches at 1600'. 46 mile received 10 inches of accumulation and .65 inches of  SWE.  Thompson Pass was guestimated at 6-8 although strong wind redistribution made actual measurement impossible.  Wind gusts up to 60 mph were recorded on Thompson Pass and up to 20 mph at the Nicks Snotel.  

Upper elevations, and areas in close proximity to Thompson Pass will be the most prone to human triggers today.   Shooting cracks and collapsing will be direct indicators of instability.  Avoid slopes steeper than 32° where signs of instability are present especially above terrain traps.  The hazard will remain low at lower elevations where accumulations were lighter and winds were not as strong and vegetation limited snow transport.  

This new round of snow is falling on surface hoar in specific locations.  This includes areas below 4000' where a strong inversion line sat last weekend, and in areas that were protected from the strong NE winds of last weekend.  It is unlikely that the amount of snow we received yesterday will be enough to make this layer a problem.  .The exception would areas where wind from yesterday created stiffer slabs.  These locations will be isolated.  Areas that received wind yesterday, would've likely received wind during the last clear and cold outflow event and surface would have been destroyed.  This layer may become a future avalanche problem with subsequent loading in the wind protected areas mentioned above.

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