Forecast Expired - 12/28/2020

Above 4,000ftModerate

2,000 to 4,000ftModerate

Below 2,000ftModerate

Degrees of Avalanche Danger

Avalanche Problems

Problem 1

Wind Slab:

Strong northeast winds and light snowfall occurred on 12/26 at Thompson Pass and high elevations.  Wind speeds briefly hit 40 mph before quickly dying off and switching to SE later in the day.  Low lying areas remained calm.  With the significant amount of loose snow available for transport wind slabs built  in areas like Thompson Pass and exposed ridge lines.  Wind slabs 1-2 feet deep may be reactive on a variety of aspects due to changing wind directions.  Encountering hollow drum like snow will indicate that you have found wind slab and shooting cracks will tell you that it still has energy and the ability to create an avalanche.  Pay attention to the way the wind has shaped terrain features in the area you are traveling to help create a picture of the way new snow has been redistributed across terrain.  Avoid terrain traps.





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


  • Historic
  • Very Large
  • Large
  • Small


  • Increasing
  • Steady
  • Decreasing

Problem 2

Persistent Slab:

There are a variety of layers that have formed in our low elevation snowpack in the Continental zone and eastern side of our Intermountain area. These include a layer of buried columns from 12/19, buried surface hoar (12/14) and facets that are growing on top of the 12/1 rain crust.  Some of these layers have been reactive as recent as 12/24.  The snowpack in the direct vicinity of Thompson Pass has been found to be much more homogenous (strong).  

There is quite a bit of spatial variability present in our snowpack.  Meaning that structure of the snowpack changes quite a bit with elevation and location.  Don’t assume that since you have experienced stable riding conditions on Thompson Pass, that everywhere will be the same.  Re-assess the snowpack when traveling in new areas.   Human triggered avalanches up to a meter deep are still possible in isolated locations.  Avoid consequential terrain north of Thompson Pass below 3000′.   Be wary of thin/rocky high elevation areas where it may be possible to affect weak layers at the bottom of the snowpack and trigger very large destructive avalanches.  


An observer on 12/24 reported remote triggered avalanches up to 100 meters away that failed a meter deep.  





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


  • Historic
  • Very Large
  • Large
  • Small


  • Increasing
  • Steady
  • Decreasing

Avalanche Activity

12/24- Observers reported remote triggered avalanches up to 100 meters away that were a meter deep.  Tsaina trees below 3000′.

12/23- DOT mitigation work on snow slide gulch produced 3 D2.5’s that ran half of their path.

-Multiple D2-D2.5 slides on Oddessey and Little Oddessey.  NW-N aspects.  Only Little Oddessey crown was clear.  ~100 yards wide, ~4′ deep.


















-Natural D3 avalanche on Billy Mitchell NW-N aspects, originated ~5000′ stepped down to the ground around 4200′ in rocky terrain. Approximately 200 yards wide.



















-Natural D2 avalanche activity was also noted on west aspects of 40.5 mile and Iguana Backs ~3500′.  Further observations were prevented due to poor light.

12/20- A powder cloud reached the highway at the mp 42 slide path. “Three Pigs”.  No other details available


-Numerous small (3-4″ deep) natural avalanches were observed in the Python and Cracked Ice Buttress area.
















12/20- Multiple D1 soft slabs off Mt Cheddar Cheese Wedge (Hippie Ridge) originating from ~6500′























12/3- Numerous natural avalanches were observed north of Thompson Pass with many avalanches failing at the ground.  Observations were not made south of Thompson Pass.

Avalanches observed from 46 mile towards Thompson Pass:

Three Pigs: Nearly every path on the SE face ran with debris deposits stopping  in the top 1/3 of aprons, thick alders prevented slides from running full path.  These were mostly D3 avalanches.

40.5 Mile Peak: Many paths running similar to Three Pigs, with one running full path to the Tsaina river.  Mainly W-NW aspects, D3’s

Max High (Peak on the southern extent of Hippie Ridge)  had a D3 avalanche with a crown near 5500′,SW aspect.

Upper Catchers Mitt bowl E aspect, slid R4-D3 ,triggering further avalanches lower down.

The main activity noted, was on the buttresses on the east side of the pass, from Cracked Ice through North Odessey Gully.  Every buttress had significant avalanche activity originating ~4000-5000′.  Many of these failed at the ground, north – northwest aspect.   Pictures below.

School Bus and North Odyssey Gully both ran with debris in the runouts.  


Many other large to very large natural avalanches occurred.




12/2- DOT reported a natural D2.5-3 avalanche that hit the Lowe river at Snowslide Gulch.

11/30- Natural avalanche observed on 40.5 mile peak just to the South of the Shovel.  West aspect, ~4500′, crown ~200′ wide, poor light prevented further observation.  SS-N-R1-D2-U.

11/29: Natural avalanche observed on Billy Mitchell Cry babys shoulder, similar elevation as 11/16 slide but originated a couple hundred meters further west.  Released from ~4000′ with a crown length of ~ 200 meters, North aspect, ~ 37°, failed at the ground.  HS-N-R2-D2.5-G 

11/16: Natural avalanche observed on Billy Mitchell “Cry babys shoulder”.  Released from~3500′ with a crown length of ~200 meters, North aspect. This slide was triggered by recent NE wind cross loading the slope.  SS-N-R2-D2-U

11/15: Natural avalanche observed in Loveland Basin on a South aspect, down the ridge from Tones Temple.  This slide was triggered by recent NE wind loading and failed at the ground. SS-N-R1-D2-G






12/27- Increasing clouds and chances of precipitation arrive with a decaying front that will move onshore towards the evening

The Thompson Pass Mountain Forecast covers the mountains (above
1000 ft) surrounding Keystone Canyon through Thompson Pass to
Worthington Glacier.

This forecast is for use in snow safety activities and emergency

                   Today        Tonight

Temp at 1000`      31 F         28 F

Temp at 3000`      25 F         25 F

Chance of precip   70%          80%

Precip amount
(above 1000 FT)    0.06 in      0.15 in

Snow amount
(above 1000 FT)    1 in         1-2 in

Snow level         sea level    sea level

Wind 3000` ridges  SE 9-15 mph  E 12-20 mph

Date: 12/27 24 hr snow (inches) HN24W (snow water equivalent inches) High Temp (F) Low Temp (F) Weekly SWE Inches (Monday-Sunday) December snowfall Season snowfall HS (snowpack depth inches)
Valdez 6 .4 33 28 2.18 48 91 41
Thompson Pass N/O N/O 25 12 ~3.35 ~107 ~225 ~66
46 Mile 3 .2 17 6 2.32 45 74 31

Thompson Pass weather history 20/21.  Click on links above the images to see full size view


November 2020

TP as of 12/21













Additional Information


12/21-12/23-  Major winter storm brings strong winds, increasing temperatures and 36″ of snow and 3.35″ of SWE to Thompson Pass at road level.

12/19-12/20- Continued stormy weather incrementally deposits ~12 inches of low density snow.  Top 3-4 inches doesn’t bond well to underlying snow and is reactive on 12/20 in multiple locations.

12/17-12/18- Significant north winds along with light snow has built wind slabs on lee aspects.  These slabs may be sitting on persistent grains such as near surface facets in some locations.

12/13-12/16-  Light snow has been falling and has landed on surface hoar below 3000′.  This layer exists north and possibly south of Thompson Pass.  On Thompson Pass proper, buried surface hoar is unlikely due to wind.  So far there is an insignificant amount of snow to overload these layers and create dangerous conditions.  This will be a layer to watch below 3000′ once more snow accumulates, possibly by this weekend.  If you have observed surface hoar in the Port of Valdez area leave an observation.

12/8-12/12- Clear cold and calm was the theme during this period.  With this, surface hoar has begun to form below 3000′.  On 12/12 surface hoar was found to exist up to 1.5 cm in length on flat benches.  On slopes the size was 2-4 mm.  SH has not been observed in high elevation start zones.  If conditions remain calm before the next snowfall this will form a sensitive layer in our snowpack in our low and mid elevation bands.






























12/5-12/7- Thompson Pass received 23 inches of snow with 2.23″ of SWE.  Temperatures and freezing line rose mid storm bringing rain to the coast.  



NE winds began 12/4 and have redistributed the storm snow onto lee aspects.  This wind event has not been widespread and appears to be concentrated to areas in close proximity to Thompson Pass.


November was mostly dominated by clear, cold and windy weather.  On 11/25 a major wx pattern shift occurred which produced 8 days of consecutive storms that delivered 10 inches of water and 90″ of snow to Thompson Pass.  This storm fell on a thin snowpack with poor structure near the ground.  On 12/1-12/2 a widespread natural avalanche cycle occurred with many avalanches failing at the ground.  This event was caused by 4.6″ of SWE on Thompson Pass in a 72 hour period along with rising temperatures bringing the freezing line up to 3000′. 



The avalanche hazard is Moderate at all elevations.  It will be possible to trigger lingering windslabs 1-2 feet deep in specific locations.  Watch for reactive wind slabs in high elevation start zones on the lee side of ridges and in cross loaded gullies.  In addition to wind slabs, persistent weak layers exist in isolated locations north of Thompson Pass below 3000′.  Avoid steep unsupported terrain on the north side of the pass below 3000′, and watch out for signs of instability in old wind slabs.

For more information click the (+full forecast) button below.

Submit a public observation to help create a picture of our constantly changing snowpack.  Visit our observation page to leave a comment or you can email me direct at [email protected]