Avalanche forecast

Continental

Valdez Avalanche Center
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Avalanche danger

Alpine
3 · Considerable
Treeline
3 · Considerable
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Out of date — this forecast expired 2 years ago.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 remains Considerable above 2000 feet. Freshly formed wind slab avalanches will be likely for a person or machine to trigger up to 1 foot in depth.  There is the possibility that a wind slab avalanche could step down to deeper layers in the snowpack and create very large avalanches.  The avalanche hazard is low below 2000 feet as a previously rain saturated snowpack has refrozen and gained strength.

Avalanche forecasts are issued Wednesday-Sunday at 8 am.

Avalanche problems

  • Wind Slabs

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

    North outflow winds kicked up to 30 mph on Thompson Pass with gusts to 40 in response to what should be a clear day today.  Other stations also show an uptick in wind speed, but with lower strength.  This increase in wind is expected to have already peaked overnight and is forecasted to fall throughout the day as the approach of the next storm system allows the for pressure gradients to slacken.

    There is an abundant amount of dry snow available for transfer above 2000', allowing for rapid wind slab development overnight.  The limiting factor will be the amount of time that moderate to strong winds occur, which is expected to be short.  The combination of these two factors is expected to leave us with wind slabs up to 1 foot in depth in specific areas.  These include the lee side of high elevation ridge lines, cross loaded gullies, and lee side of terrain features that are close to wind channeled terrain such as Thompson Pass summit.

    Watch for signs of current wind redistribution such as flagging, and look for signs of previous wind loading like textured snow surfaces, and fresh windlips that will point towards wind loaded slopes.  Wind slabs are the most sensitive while they form and directly after, which will be today.  These can be visually identified as having a rounded pillowed look, or may have a rippled texture.  

    It is possible that wind slab avalanches could step down to deeper layers in the snow in isolated areas and create very large avalanches. (see problem2)

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

    Photo: Gareth Brown

  • Deep Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    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 natural and artillery triggered avalanches the result.  

    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 remains possible to trigger one of these avalanches in isolated areas where a human triggered wind slab avalanche is able to step down to old weak layers or in an areas where the storm slab is thin.  To steer clear of this problem, users could avoid large steep open slopes with connected terrain features in the 2500-3500' elevation band.  Maintaining good travel protocols is especially important when persistent problems may exist.  These include good communication, only exposing one person to an avalanche prone slope at a time, and grouping up well out of the way of runout zones.

    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: 

Natural and artillery triggered D2.5-D3 avalanches were observed on all aspects from: Hogsback ridge, Snowslide Gulch, Above Bear Creek, Loveland Basin, Catchers Mitt, School Bus, Odessey, Gully 1,2,and Nicks, Python Buttress, Python summit, Berlin Wall, Girls, Bro Bowl, East of Averys, Cracked Ice, Three Pigs, 40.5 Mile, Billy Mitchell and Mt. Tiekel.  More info available by clicking the Weather history tab or the Avalanches tab just below the bottom line statement.

Forecast Discussion:

Our snowpack has undergone a major transition after a prolonged period of snowfall that fell mostly above 2000'.  From 1/4-1/13 Thompson Pass DOT has recorded 168" of snowfall, with 100" of that falling in a 2 day period 1/11-12.  This has opened up a significant amount of access as bushes have largely been laid over above 2000'.  

Observations from the field over the last two days have found a snowpack that is accepting the new weight of the snow, and is without any major flaws in the deep storm slab.  There was a lot of wind with the major snowfall of this weekend so areas near wind channeled areas of Thompson Pass have shown variable storm slab depths with deep wind drifts in places.  Further away from the pass storm slabs were found to be more homogenous and right side up.  Deep persistent weak layers are now difficult to detect when probing but are likely 2 meters or more deep at this point.  This makes it difficult for a person to directly trigger them, but if they were initiated, the result would be catastrophic.

Wind slabs that formed overnight will be the most likely problem for people to encounter today and are expected to be in the 6-12" range in depth as moderate winds are only expected to be present for a short period of time.  These are expected to be more concentrated towards the wind funnel of the Thompson Pass summit.  

A cautious and conservative Considerable hazard rating continues to be applied to the forecast due to the possibility of smaller avalanches stepping down to deep layers in isolated areas that could produce VERY LARGE avalanches.  In areas that saw the heaviest winds during the storm, it may also be possible to trigger these deeper layers where the recent storm slab is thinner.  The possibility of this is decreasing as time allows the snowpack to settle and field observations show a strong right side up upper snowpack.

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- 1/15 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    -    103     N/O 46 Mile    0     ~   20    10 N/O

Regions covered