Forecast Expired - 12/05/2021

Above 4,000ftConsiderable

2,000 to 4,000ftConsiderable

Below 2,000ftModerate

Degrees of Avalanche Danger

Avalanche Problems

Problem 1

Wind Slab:

It has been 48 hours since the onset of the latest wind event.  If we had a normal/strong snowpack in place we would begin expect windslabs to become less sensitive to triggers.  In the current situation, windslabs are sitting on weak faceted snow and it will remain likely to trigger wind slab avalanches on lee aspects 1-2 feet in depth.  A cautious approach is necessary when traveling anywhere in avalanche terrain at the moment.  But, is especially apparent in areas where there is hard snow over soft indicating that a slab is present. 


   Cautious terrain choices and careful terrain management will be necessary today to travel in areas recently affected by wind.  Watch for signs of windslab that include hard snow over soft, shooting cracks, collapsing and rounded pillowed snow surfaces.  Avoid traveling on large lee slopes steeper than 32°.



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


  • Historic
  • Very Large
  • Large
  • Small


  • Increasing
  • Steady
  • Decreasing

Problem 2

Persistent Slab:

The cold and dry weather in November has left us with a weak faceted snowpack.  In areas protected from the wind there is 10-20 inches of dry unconsolidated powder.  The most important thing to pay attention to at the current time is how stiff or slabby the surface snow is.  The stiffer the surface snow is, the higher the likelihood will be for you to trigger an avalanche on terrain steeper than 30°.  In areas where the snow surface is dry and unconsolidated (no slab) the stability has been found to be better although structure is still poor, and human triggered avalanches are possible.  As snow surfaces stiffen human triggered avalanches become likely.  Keep an eye on your partners and only expose one person at a time to avalanche prone slopes.


Don’t expect to find the same snow stability across the forecast area. Re-assess the snowpack every time you are traveling to a new location.  Digging snowpits is a good way to asses a snowpack when persistent weak layers exist.


Photo of 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

12/2-12/3- 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


* WHAT...Heavy snow possible. Total snow accumulations of 18 to
  28 inches possible.

Point forecast for Thompson Pass


Mostly cloudy, with a high near 5. Wind chill values as low as -35. Northeast wind 25 to 30 mph, with gusts as high as 35 mph.
Mostly cloudy, with a low around 1. Northeast wind 20 to 25 mph.
Snow, mainly after 9am. High near 16. Northeast wind 10 to 20 mph becoming south in the afternoon. Winds could gust as high as 25 mph. Chance of precipitation is 90%. New snow accumulation of 1 to 2 inches possible.
Sunday Night
Snow. Low around 16. South wind around 15 mph. Chance of precipitation is 100%.
Snow. High near 22. South wind around 10 mph. Chance of precipitation is 90%.
Monday Night
Snow. Low around 20. Southeast wind 5 to 10 mph. Chance of precipitation is 90%.
Snow, mainly before 3pm. High near 24. Chance of precipitation is 80%.

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

DATE             SATURDAY 12/04          SUNDAY 12/05            
TIME (LT)        06    12    18    00    06    12    18    00    06
CLOUD COVER      OV    OV    OV    OV    OV    OV    OV    OV    OV
CLOUD COVER (%)  75    75    80    85    85    95   100   100   100
TEMPERATURE      -4     3     5     7    10    15    18    19    21
MAX/MIN TEMP                  7           2          17          17
WIND DIR         NE     E    SE    SE    SE    SE     S     S     S
WIND (MPH)        8     6     6     8    11    12    14    13    10
WIND GUST (MPH)  35    32    27    26                              
PRECIP PROB (%)  10    10    10    20    60    90    90    80    80
PRECIP TYPE                         S     S     S     S     S     S
12 HOUR QPF                0.00        0.01        0.16        0.54
12 HOUR SNOW                0.0         0.0         2.4         8.5
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: 12/04 24 hr snow  HN24W* High Temp Low Temp Weekly SWE (Monday- Sunday) December Snowfall Season Snowfall HS (Snowpack depth)
Valdez 0 0 16 -1 .54 13 38 17
Thompson Pass 0 0 wx station down wx station down .9 11 130 30
46 Mile 0 0 6 -12 .32 5 5**  12


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.  This moderate outflow wind event resulted in the formation of wind slabs that were very reactive to human triggers.  This is yet another sure indicator of the weaknesses present in our snowpack.



The avalanche hazard remains Considerable at mid and upper elevations in areas where recent winds have created windslabs.  Triggering a windslab 1-2 feet in depth is likely today on slopes steeper than 32°.  The hazard is moderate in areas protected from the wind where it is possible to trigger a persistent slab avalanche.


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