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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Out of date — this forecast expired 2 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

The avalanche hazard is Moderate above 2000 feet and Low below.  Human triggered avalanches are possible up to 1 foot in depth on recently wind loaded slopes.  Natural avalanches are unlikely. 

Avalanche forecasts are issued Wednesday-Sunday at 8 am.

Avalanche problems

  • Wind Slabs

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

    A brief North outflow wind event on the 15th-16th formed wind slabs in specific areas up to 1 foot in depth.  These are gaining strength, but may still be possible to trigger in isolated areas.  Winds have since shifted to southerly which may form fresh wind slabs, mostly just below high elevation ridge lines, and cross loaded gullies.  These are not expected to be deep or widespread but could be a hazard in steep terrain.  Paying attention to aspect will be important today as old wind slabs that are unreactive may exist on SE-NW aspects. In contrast, fresh more sensitive windslabs may exist on northerly aspects.  

    You can tell the difference between the two of these by what aspect they exist on and their hardness.  Older wind slabs have locked up by now and will be 1 finger to pencil hard.  Fresh wind slabs will be softer at 4 finger-1 finger hard and may exhibit signs of instability such as shooting cracks.  

    Flagging off high elevation ridges near Thompson Pass the evening of the 15th

    Photo: Gareth Brown

  • Deep Persistent Slabs

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

    Prior to last weekends snowfall event there were multiple persistent weak layers that were being tracked, including a couple of layers of buried surface hoar and a rain crust sandwich with facets in the middle.  These exist primarily in the mid elevation band and a couple of them were beginning to show propagation in stability tests as snow steadily accumulated from the 4th-10th.  The 11th-12th brought 100" of snowfall to Thompson Pass in 48 hours which overloaded these layers in many areas with a significant natural avalanche cycle.

    These layers are now deeply buried by 1.5-2 meters or more of settled storm snow.  As precipitation has taken a break, the snowpack is allowed to settle and slowly accept the weight of this new snow.  Over time, this decreases the likelihood of human triggered avalanches at these layers due to their depth and an overall decrease in sensitivity.  

    It is now unlikely to affect these deep layers and trigger one of these avalanches.  We are leaving this problem on our list for the time being as a conservative approach until we can test a wider variety of areas to confirm better structure and lower sensitivity than what existed prior to last weeks storm.

    If this problem were to arise it would probably be in an area where the recent storm snow was thin due to wind redistribution during the storm, with steep convex slopes in the mid elevation band.  Thin, rocky areas in steep terrain could be a place where trigger points exist as well.

     

    Natural avalanches from 1/12 that failed at a deep persistent weak layer.  

    It is possible these released sympathetically from the artillery triggered school bus slide.

    Photo: Gareth Brown

Avalanche Discussion

Observed Avalanche Activity last 72 hours: 

NONE.  

More info is available about the last avalanche cycle by clicking the Avalanches tab or the weather history tab just below the bottom line statement.

Forecast Discussion:

The last few days of mostly benign weather has allowed our snowpack to slowly gain strength following the heavy snowfall and High avalanche danger of last weekend.   Today will be the last day of benign weather as heavy snowfall above 1500' and rain below will return to the forecast area on Sunday.  

Today, the main concern for users will likely revolve around surface instabilities created by the wind.  A mix of old stubborn wind slabs from North outflows and fresh, more sensitive wind slabs from southerly wind should be expected.  The fresh wind slabs are expected to be concentrated near high elevation ridges, but might be more widespread in close proximity to wind channeled terrain such as Thompson Pass Summit.

We need more data points before we can remove the deep persistent problem.  However, everything we have seen so far after the storm is pointing towards improving stability.

Additional Information:

A weather and snowpack season history is available by clicking on the Weather History tab that is located above the bottom line statement once you have entered the full forecast.

Glide cracks that existed on the buttresses from Nicks through Cracked Ice on North aspects at mid elevation were stagnant prior to the recent snowfall and are now filled in.  It will be worth watching for them to reappear, but this may be a problem of the past.

Season Snowfall Data

Location 24 hour Snowfall Inches- 1/18 24 hour Snow Water Equivalent Inches Height of Snow January Snowfall Inches Season Total Snowfall Valdez     0    ~    19     10     45 Thompson Pass    0    ~   N/O    170    N/O Nicks    0    -    94     N/O 46 Mile    0     ~   20    10 N/O

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