Forecast Expired - 12/10/2021

Above 4,000ftConsiderable

2,000 to 4,000ftConsiderable

Below 2,000ftConsiderable

Degrees of Avalanche Danger

Avalanche Problems

Problem 1

Persistent Slab:

The 12/5-12/6 storm that deposited 2 feet of snow in Valdez and 12-16″ on Thompson Pass, has increased the depth of the slab that is sitting on the November facets.  On 12/8 a remote triggered/sympathetic avalanche event (see observation section) is a clear sign that our persistent slab avalanche problem is hanging on by its fingernails.  This is especially true in wind sheltered areas.  In locations were old wind slabs exist above the November facets, weak layers may be more stubborn to triggers.  But the same weak layer exists and dangerous human triggered avalanches are possible in these locations as well.  


The next storm is on tap for our area beginning this afternoon with 4-8″ of snowfall and moderate to strong east winds that will eventually turn to northeast.  This will further build Persistent slab depths, but will probably not be enough to cause a natural avalanche cycle.  As the next storm exits strong northeast winds will turn on.  It is possible this will be enough to create some natural avalanche activity on southerly aspects.


The 24 hour rule will not apply for our current setup.  The only successful mitigation practices for a persistent slab avalanche problem are patience, and a conservative approach in choosing terrain.  Good protocols are very important as well during this type of avalanche problem ie: only exposing one person at a time to an avalanche prone slope, good communication and having an escape route should a slope fail.


Some important things to remember about a persistent weak layer problem is that tracks are not a sign of stability.  A slope can fail after many tracks have been laid down.  Also it will be possible to trigger avalanches remotely meaning a slope that is above you or adjacent to your position. 


Photo of Remote triggered/sympathetic avalanches on 12/8 


1cm+ chained facet found buried 40 cms (16″) on Catchers Mitt 3500′ SE aspect.




  • Almost Certain
  • Very Likely
  • Likely
  • Possible
  • Unlikely


  • Historic
  • Very Large
  • Large
  • Small


  • Increasing
  • Steady
  • Decreasing

Problem 2

Wind Slab:

East winds are expected to be moderate to strong today as snowfall arrives. As the storm exits winds will ratchet up and move to northeast.  Expect to find fresh wind slabs up to 2 feet in depth in wind channeled terrain that will be reactive to human triggers.  Wind slab avalanches will have the potential to step down into deeper faceted layers in our snowpack (see problem 1) and produce larger avalanches.  Avoid recently wind loaded slopes in terrain steeper than 32°.







  • Almost Certain
  • Very Likely
  • Likely
  • Possible
  • Unlikely


  • Historic
  • Very Large
  • Large
  • Small


  • Increasing
  • Steady
  • Decreasing

Avalanche Activity

12/8- Large remote trigger/ sympathetic avalanche event occurred 12/8 with avalanches extending from Gully 1 to Nicks.  Avalanches were soft slabs that ranged in size from D1-D3.  8 separate avalanches were counted with crown depths averaging 2-3′.  One avalanche had a crown length of half a mile while another was triggered over a mile away from the point of collapse.  See observation section for full report and more photos.

12/7- Only a few natural avalanches were noted during the last storm.  It is likely there were more during the storm, but crowns may have been filled in by subsequent wind and snow.

D2 on Town mountain was observed ~3000′

A couple of D2’s were noted in N. Oddessey gully and Big Oddessey.

D2 on 40.5 mile peak ~5500′.

12/2-12/3- Several natural D2 avalanches were noted on south aspects of Three pigs, Hippie Ridge and Averys.  These windslab avalanches originated between 4000-5500 feet elevation.


NWS Watches and Warnings


Point forecast for Thompson Pass


Snow, mainly after noon. Areas of blowing snow after noon. High near 17. Northeast wind 10 to 15 mph increasing to 15 to 20 mph in the afternoon. Winds could gust as high as 25 mph. Chance of precipitation is 100%. Total daytime snow accumulation of 1 to 2 inches possible.
Snow. Areas of blowing snow before midnight. Low around 8. East wind 20 to 25 mph decreasing to 15 to 20 mph after midnight. Winds could gust as high as 35 mph. Chance of precipitation is 100%. New snow accumulation of 3 to 5 inches possible.
Snow before 9am, then snow showers, mainly after 9am. Areas of blowing snow after noon. High near 19. Northeast wind 20 to 25 mph, with gusts as high as 30 mph. Chance of precipitation is 90%. New snow accumulation of around an inch possible.
Friday Night
Scattered snow showers before 3am. Areas of blowing snow. Mostly cloudy, with a low around -2. Wind chill values as low as -30. Northeast wind 25 to 30 mph increasing to 35 to 40 mph after midnight. Winds could gust as high as 50 mph. Chance of precipitation is 50%.
Areas of blowing snow. Partly sunny, with a high near 9. North wind 20 to 30 mph, with gusts as high as 35 mph.
Saturday Night
Areas of blowing snow before 9pm. Partly cloudy, with a low around -8. North wind 25 to 30 mph decreasing to 15 to 20 mph in the evening. Winds could gust as high as 40 mph.
A 30 percent chance of snow after 3pm. Partly sunny, with a high near -5.
Sunday Night
A chance of snow. Mostly cloudy, with a low around -13.

 Detailed forecast for Thompson Pass (mid elevation 2000-4000′)

DATE             THURSDAY 12/09          FRIDAY 12/10            
TIME (LT)        06    12    18    00    06    12    18    00    06
CLOUD COVER      OV    OV    OV    OV    OV    OV    BK    BK    BK
CLOUD COVER (%)  75   100   100   100    95    85    65    65    65
TEMPERATURE       9    17    14    12    12    18     8     2     4
MAX/MIN TEMP                 18          10          20           0
WIND DIR          E     E     E     E     E    NE    NE    NE     N
WIND (MPH)        8    20    32    17    18    17    18    26    18
WIND GUST (MPH)        40    55    34                39    51      
PRECIP PROB (%)  20   100   100   100    90    80    50    30     5
PRECIP TYPE       S     S     S     S     S     S     S     S      
12 HOUR QPF                0.14        0.38        0.07        0.04
12 HOUR SNOW                2.2         6.8         1.2         0.0
SNOW LEVEL (KFT)0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0

Snow and Temperature Measurements


Date: 12/09 24 hr snow  HN24W* High Temp Low Temp Weekly SWE (Monday- Sunday) December Snowfall Season Snowfall HS (Snowpack depth)
Valdez 0 0 30 9 1.48 39 64 32
Thompson Pass 0 0 17 6 1.2 26 145 36
46 Mile 12 12**  13


All snowfall measurements are expressed in inches and temperature in Fahrenheit. 24 hour sample period is from 6am-6am. 

* 24 hour snow water equivalent/ SWE.

** Season total snowfall measurements for 46 mile began December 1st.


Season history graphs for Thompson Pass

















Click on links below to see a clear and expanded view of above Season history graphs


TP WX as of 11/29



Additional Information

Winter weather began early this season, with valley locations receiving their first snowfall on the last day of Summer (September 21st).  Following this storm, above average temperatures and wet weather occurred from late September through early November.  During this time period Thompson Pass received 96 inches of  snowfall by November 7th and Valdez recorded 7.73″ of rain.  

After the 7th of November our region experienced a sharp weather pattern change.  Temperatures dropped below seasonal norms and snowfall became infrequent.  Between the time frame of November 7th- November 28th Thompson Pass only reported 19″ of snow with 1.1″ of Snow water equivalent (SWE).  Temperatures remained below 0° F for most of the period.   This cold/dry weather caused significant faceting of the snowpack, with poor structure the result.

Moderate snowfall returned to our area the last day of November and deposited 6-12 inches of new snow.  The amount varied depending upon the locations’ proximity to the coast.  As the storm exited on the 2nd of December it was quickly replaced by moderate to strong northeast winds.  

On 12/5-12/6 Valdez received 2 feet of new snow with Thompson Pass reporting 16″.  Blaring red flags like collapsing, shooting cracks and propagation in stability tests were immediately present.  This indicates we have moved into persistent slab avalanche territory.



The avalanche hazard is Considerable at all elevations.  Triggering an avalanche 2-3 feet deep will be likely today that could injure, bury or kill a person.  Careful snowpack assessment and conservative terrain management will be necessary today if you choose to travel in avalanche terrain.


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