Forecast Expired - 12/18/2021

Above 4,000ftModerate

2,000 to 4,000ftModerate

Below 2,000ftModerate

Degrees of Avalanche Danger

Avalanche Problems

Problem 1

Persistent Slab:

There is a 2-3+ foot deep slab sitting on the November facets.    These facets have continued to show easy to moderate propagation results in ECT and PST stability tests.  Red flags such as shooting cracks, large collapses and natural avalanches have been present in the Thompson Pass area lately.  This is a bullseye indicator that our persistent avalanche problem is still active.


 Very strong northeast winds have recently loaded lee aspects, further stressing facets in these areas.  In areas exposed to wind, the slab overlying the November facets has variable depths.  These range from scoured down to the facets (little to no slab) on windward aspects, to 2-4 feet deep on lee aspects (dense wind slabs).  In areas exposed to recent winds the avalanche problem is confined to specific areas (lee aspects).


 In areas sheltered from the wind the slab thicknesses are more uniform.  In these area the persistent avalanche problem is widespread.  A skier or snowmachine may be able to directly affect these weak layers and could trigger avalanches in terrain steeper than 30°.  With this type of avalanche problem it is also possible to trigger avalanches remotely from flat terrain.  At the present moment this problem layer is 2 feet deep in most locations.  Red flags such as collapsing and shooting cracks are a sign that slopes steeper than 30° could produce an avalanche.



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.



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:


Triggering a wind slab avalanche 2 feet deep remains possible today on lee aspects (SE-NW) of terrain recently exposed to wind.   It is becoming less likely to trigger wind slabs as we get further from the most recent loading event.  Although,  wind slabs will maintain a possibility to be triggered since they are sitting on weak snow (facets).   The most likely areas to find this problem still reactive would be on steep lee aspects near a thin section of a slab where a person or snow machines weight could affect faceted snow beneath denser slabs.  The hardness of slabs may allow a person out onto a slope and fail behind them.

 Wind slab avalanches will have the potential to step down into deeper faceted layers in our snowpack, (see problem 2) and produce larger avalanches.  Current wind slabs will present as hard snow over soft and will have a hollow drum like feel.  The hazard for this avalanche problem will be slowly decreasing as the snowpack adjusts to this new layer.




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


  • Historic
  • Very Large
  • Large
  • Small


  • Increasing
  • Steady
  • Decreasing

Avalanche Activity

12/14-  Several natural avalanches were observed although poor visibility prevented a full view of the action.  The most notable natural was observed in Nicks Happy Valley on a NW aspect ~4000′.  Crown depth was not visible.  Debris ran down the valley and piled up at the typical snowmachine pickup.

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.  Over 10 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’s 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 showers likely, mainly before 9am. Mostly cloudy, then gradually becoming sunny, with a temperature falling to around 4 by 1pm. North wind 15 to 20 mph. Chance of precipitation is 60%. Total daytime snow accumulation of less than a half inch possible.
Increasing clouds, with a low around 4. North wind 5 to 10 mph becoming light and variable after midnight.
A slight chance of snow between noon and 3pm. Mostly cloudy, with a high near 16. Light and variable wind becoming northeast 20 to 25 mph in the afternoon. Chance of precipitation is 20%.
Saturday Night
Partly cloudy, with a low around 10. Northeast wind 30 to 35 mph, with gusts as high as 45 mph.
Partly sunny, with a high near 17. North wind 25 to 30 mph, with gusts as high as 40 mph.
Sunday Night
Partly cloudy, with a low around 9. North wind around 15 mph, with gusts as high as 30 mph.
Partly sunny, with a high near 20.
Monday Night
Snow likely after 9pm. Mostly cloudy, with a low around 11.

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

DATE             FRIDAY 12/17            SATURDAY 12/18          
TIME (LT)        06    12    18    00    06    12    18    00    06
CLOUD COVER      OV    FW    SC    OV    OV    OV    SC    FW    SC
CLOUD COVER (%)  80    20    35    75    70    75    45    15    40
TEMPERATURE      11     6     7    11    13    17    13    13    12
MAX/MIN TEMP                 15           6          18          10
WIND DIR         NE    NE     E     S     S    NW    NE    NE    NE
WIND (MPH)        8    10     5     3     3     5    17    19    16
WIND GUST (MPH)                                23    46    46    40
PRECIP PROB (%)  60     5     0     5    10    20     5     0     0
PRECIP TYPE       S                             S                  
12 HOUR QPF                0.02        0.00        0.01        0.00
12 HOUR SNOW                0.2         0.0         0.0         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: 12/17 24 hr snow  HN24W* High Temp Low Temp Weekly SWE (Monday- Sunday) December Snowfall Season Snowfall HS (Snowpack depth)
Valdez 4 .3 24 14 .1 48 72 22
Thompson Pass N/O N/O 20 9 .2 36 155 24
46 Mile N/O N/O .25 25 25**  19


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.  On 12/8 a significant remote/ sympathetic avalanche event occurred from Gully 1 through Nick’s Happy Valley. 

Strong outflow winds began on 12/11 with periods of light snowfall.  This has caused slab thicknesses to become variable in areas exposed to NE winds.



The avalanche hazard is Moderate at all elevations.  Triggering an avalanche 1-3 feet deep will be possible today.  Watch for red flags such as shooting cracks and collapsing that indicate areas of unstable snow..


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