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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Highlights

The avalanche hazard is CONSIDERABLE above 2000 feet and low below.  Today it will be possible to trigger an avalanche at layers within the recent storm snow.  There is the potential for human triggered avalanches to step down to deeper layers in the snowpack creating very destructive avalanches. The hazard is low below 2000 feet where a previously rain saturated snowpack has refrozen and gained strength.

Avalanche problems

  • Storm Slabs

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

    Yesterday we received our first break from a prolonged period of snowfall that peaked in intensity over the weekend.  Thompson Pass DOT has reported 100 inches of snowfall during the Saturday-Sunday time period.  During this period of intense snowfall the snowline hovered around 2000 feet before dropping to near 1000' and finally sea level for a brief period at the end of the storm.  Winds were very strong during peak snowfall intensity primarily from the south, but natural avalanche patterns indicate north winds near the pass were also occurring.  At 5:30 am this morning, light snow was falling at sea level, but is not expected to be sufficient to affect the stability, light winds are expected.

    There is still very little known about the stability of the recently fallen snow, but there are some things we can be sure of.  First is that strong winds and fluctuating freezing line will have created uneven storm slab distribution with multiple density changes likely to exist in the thick storm slabs.  These density changes could act as failure planes that could be triggered by a person.  A considerable tag has been applied to this forecast because of the uncertainty of the new snow stability along with the potential that smaller human triggered avalanches may have the potential to step down to deep persistent weak layers creating unsurvivable avalanches (see problem 2).  This is especially true on larger slopes greater than 30° with mutiple connected terrain features in the 3000'-4000' elevation band where a majority of the deep persistent avalanche activity occurred.

    With the amount of uncertainty that exists along with the sheer mass of new snow it is recommended to approach assessment cautiously.  Pay attention to the layering of the surface snow, is it right side up or upside down?  Are there shooting cracks or collapsing in the snowpack that would indicate the snow has the energy to produce an avalanche?    New snow fall depths may make it difficult to accurately pole probe for density changes think about using your probe in a few spots to feel for major density changes.  If you do decide to travel on slopes greater than 30°, think about keeping these slopes small in size and not connected to larger slopes.

    Safe travel protocols such as good communication, only exposing one person at a time to an avalanche prone slope and regrouping well out of runout zones will be important skills to utilize today.

  • Deep Persistent Slabs

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

    A clear day yesterday allowed a view into the mountains that revealed a significant amount of natural and artillery triggered avalanche activity that occurred this weekend.  Most of the activity likely occurred toward the tail of the storm on Sunday 1/12 judging by the crisp look of crown lines.  There was plenty of activity from upper elevations where the snowpack simply became overloaded by snow and wind, however the most notable slides were from the mid elevation bands where persistent weak layers previously existed.  

    We have received enough snow over the last 2 weeks that these layers were stressed beyond their strength threshold, resulting in a widespread avalanche cycle on all aspects.  As precipitation stopped for a day and temperatures cool, the snowpack will slowly adjust to this new load.  At this point the previous persistent weak layers of the early December rain crust sandwich and the 1/4 buried surface hoar are now buried deeply in the snowpack.  This will make them less likely for a human or machine to directly trigger especially as time moves on.

    Places where we could trigger these avalanches could be from an especially thin part of the storm slab.  Or more likely, a smaller human triggered avalanches within the most recent storm snow that could produce enough force on larger slopes to initiate a step down avalanche at one of these deep layers.  This needs to remain in our mind when planning our travel through the mountains.  This problem will remain a concern while the snowpack slowly adjusts to its new load or until more field data can be gathered.

    Travel advice consists of safe travel protocols as previously listed and conservative terrain choices.

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

    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, East of Averys, Cracked Ice, Three Pigs, 40.5 Mile, Billy Mitchell and Mt. Tiekel.  More info available by clicking 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'.  Such a sudden addition of weight to a relatively thin snowpack creates a lot of stress in the snowpack.  This stress will slowly dissipate as the new snow bonds with the underlying snowpack and will eventually add strength to accept future storms.  But, the key words are EVENTUALLY and SLOWLY.  This is a process that takes time, the 24 hour rule doesn't fully work in our current situation.  Be patient, the winter season is long and this storm will help our snowpack in the long run.  In the short term dangerous avalanche conditions remain.

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     1"    ~    19     10     45 Thompson Pass    1"    ~   N/O    170    N/O Nicks    0"    N/O    103     N/O 46 Mile    Trace     ~   20    10 N/O

Regions covered