Forecast Expired - 12/24/2021

Above 4,000ftConsiderable

2,000 to 4,000ftConsiderable

Below 2,000ftModerate

Degrees of Avalanche Danger

Avalanche Problems

Problem 1

Wind Slab:

Northerly winds are once again forecasted to become strong through the day.  This will be building windslabs on lee aspects and adding stress to a very weak snowpack.  The latest wind event on 12/21 was able to trigger numerous natural wind slabs.  In many places these were older/ deeper windslabs that were failing on facets created in November.  


There is still loose snow available for transport in places and will allow for fresh windslabs to form.  These could be reactive themselves up to 1 foot in depth, or could overload deeper persistent wind slabs creating much deeper and more dangerous hard slab avalanches.  Slopes may fail once a person has travelled well out onto the slab.  Look for signs of windslab such as pillowed smooth snow surfaces, areas that have a hollow drum-like feel and shooting cracks.  Use caution, this is not our typical Thompson Pass snowpack, expect instability to linger longer after weather events than what is typical.





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


  • Historic
  • Very Large
  • Large
  • Small


  • Increasing
  • Steady
  • Decreasing

Problem 2

Persistent Slab:

There is a 1-3+ foot deep slab sitting on the November facets.    These facets have continued to show easy to moderate propagation results in stability tests.  Red flags such as shooting cracks, large collapses and natural avalanches have all been present in the Thompson Pass area lately.  


 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 persistent avalanche problem is confined to specific areas (lee aspects).  Persistent wind slab avalanches were naturally active as recently as 12/21.  Triggering a persistent slab avalanche will be likely directly following major changes in weather, such as strong winds.  The hazard will slowly decrease as we move further away from wx events, but will remain a dangerous possibility.


  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.  It is possible to trigger avalanches remotely from flat terrain be aware of the terrain around you and the consequences of triggering a slope above you.



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

Avalanche Activity

12/21- Numerous natural avalanches observed all along the north side of Thompson Pass, as a result of strong NE wind event along with a couple inches of new snow and rising temperatures.  Observed naturals on all aspects except windward slopes with crowns originating from 1000 feet to 5500 feet in elevation.  Most of these were hard slab avalanches.  Crown depths were difficult to discern due to reloading, although some crowns looked to be up to 2 meters in depth.

12/19- D 2.5 natural avalanches were observed on the north facing buttress west of Gully 1 and Schoolbus.  

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


Areas of blowing snow. Partly sunny, with a high near 18. North wind 30 to 40 mph increasing to 40 to 50 mph in the afternoon. Winds could gust as high as 55 mph.
Areas of blowing snow. Partly cloudy, with a low around 4. North wind 50 to 55 mph, with gusts as high as 65 mph.
Areas of blowing snow before 9am. Sunny, with a high near 12. North wind 35 to 45 mph decreasing to 25 to 35 mph in the afternoon. Winds could gust as high as 50 mph.
Friday Night
Mostly cloudy, with a low around 8. North wind around 20 mph, with gusts as high as 30 mph.
Christmas Day
Mostly cloudy, with a high near 14. North wind 5 to 10 mph becoming south in the morning. Winds could gust as high as 20 mph.
Saturday Night
Mostly cloudy, with a low around 5. West wind 5 to 10 mph.
A 40 percent chance of snow after 9am. Mostly cloudy, with a high near 21.
Sunday Night
A chance of snow. Mostly cloudy, with a low around 10.


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

DATE             THURSDAY 12/23          FRIDAY 12/24            
TIME (LT)        06    12    18    00    06    12    18    00    06
CLOUD COVER      SC    BK    SC    SC    FW    SC    SC    BK    OV
CLOUD COVER (%)  40    65    50    30    15    30    40    65    75
TEMPERATURE      16    15    11     7     8    12    11    11    11
MAX/MIN TEMP                 18           5          13           9
WIND DIR         NW     N     N    NE    NE    NE     N    NE     N
WIND (MPH)       18    24    35    29    27    18    11     6     4
WIND GUST (MPH)  46    57    64    62    52    39          27      
PRECIP PROB (%)   5    10     5     0     0     0     0     5    10
PRECIP TYPE                                                        
12 HOUR QPF                0.00        0.00        0.00        0.00
12 HOUR SNOW                0.0         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: 12/23 24 hr snow  HN24W* High Temp Low Temp Weekly SWE (Monday- Sunday) December Snowfall Season Snowfall HS (Snowpack depth)
Valdez 0 0 25 7 .12 55 79 22
Thompson Pass 0 0 N/O N/O .2 39 159 24
46 Mile 0 0 6 -10 .25 28 28**  20


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 Nov 21


TP WX as of 12/20

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.

A fair amount of natural avalanche activity occurred during the 12/11 wind event mostly on southerly aspects.  The week following this wind event fairly benign weather occurred which allowed the snowpack to adjust and for stability to improve although snowpack structure has remained poor.  

On 12/21 our area received a couple inches of snow along with temperatures rising and strong outflow winds.  This combination of weather kicked off a fairly significant natural avalanche cycle.  Many of the slabs appeared to be deeper wind slabs that were created from the 12/11 wind event.  These failed on faceted snow created in November.  The event is yet another indicator of our poor snowpack structure and its inability to receive any major change in weather without the avalanche hazard rising in conjunction.




The avalanche hazard is considerable above 2000 feet.  Human triggered avalanches are likely on wind loaded aspects (SE-NW) up to 3 feet deep.  Avalanches may fail behind a person or rider, once he/she is out onto a slope.


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