Forecast Expired - 02/23/2020

Above 4,000ftConsiderable

2,000 to 4,000ftConsiderable

Below 2,000ftConsiderable

Degrees of Avalanche Danger

Avalanche Problems

Problem 1

Storm Snow:


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


  • Historic
  • Very Large
  • Large
  • Small


  • Increasing
  • Steady
  • Decreasing

Problem 2

Deep Slab:


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


  • Historic
  • Very Large
  • Large
  • Small


  • Increasing
  • Steady
  • Decreasing

Avalanche Activity

2/20: Two side by side avalanches were observed on the NW shoulder of the Python buttress ~3500′. Crown 2-300′ across and ~3’+ deep, low light made it difficult to tell how far they had run.  These slides may have been triggered by DOT mitigation work 2/19, but this is unconfirmed.

2/20: 2 paths on Three Pigs at mp 42 slid naturally to the middle to lower portion of their aprons, D2.5.  Low clouds prevented ability to see what elevation they originated from.

2/20: A Natural avalanche was reported on the north shoulder of Mt Tiekel at ~4500′.  Details were limited but the entire slope avalanched and crown was reported to be 2 meters deep. R5-D2.5~.

2/19: A Natural avalanche at 32 mile buried the Richardson higway under 10 feet of snow for ~100′.  This caused the highway to close for the majority of the day.  Details on the slide were limited due to poor visibility on 2/19.

2/14: Dry loose D1-2 natural avalanches were observed running over the wowie zowie ice climb in Mineral creek.

2/13: Natural and human triggered D1 avalanches were observed in keystone canyon.

2/12: A D3 avalanche at mile post 38 hit the Richardson highway and closed the road.  Released on a south aspect in the upper elevation start zones, ~5500′, and stepped down around 4-4500′.  Further DOT mitigation efforts on Three pigs and 40.5 mile produced no results.

2/11: Small avalanche observed on NW aspect of Dimond “promise land”, ~5500′ , R1-D1.5, wind loaded pocket just off ridge line.

-Several avalanches observed on steep benches below 2500′ on S aspect hippie ridge around MP 35.  Only ran height of bench ~100′, but had long connected crowns suggesting these failed on a Persistent weak layer. Crowns ~2′ deep.

2/10: Skies cleared yesterday, from 46 mile to Thompson Pass very few natural avalanches were seen from the 27 inches of snow that fell from 2/8- 2/10. 

2/8: Many full path avalanches were reported running around Valdez glacier lake.

2/6: 2 remote triggered avalanches on RFS at 1800-2000′.

  • SS-ARr-R1-D1-O, N aspect, 60′ wide, 50 cm crown, 1800′, failed on buried near surface facets.
  • SS-ARr-R3-D1.5-O, N aspect, 100′ wide, ~60 cm crown, 2000′, failed on buried near surface facets.

Photo of 1st remote trigger listed

-Natural avalanches observed on south aspect at mile 40, ~1800′, 1-2 feet deep and ~100′ wide. SS-NL-R2-D1.5-O.  These were triggered by small snow sluffs.

2/2: Numerous Small pockets of unsupported terrain released naturally in the tsaina valley below 2000′, 2′ deep.

1/27-1/30: Naturals were observed on RFS, N aspect ~6000′,

Avalanches were also observed on -40.5 mile, ~5000′ ,W aspect, 60 m crown

– 2 paths on Three Pigs, ~5000′, SE aspect, ran into the top 1/3 of aprons.

– 3 slides on Billy Mitchell ranging from 3000′-6000′, NW- N aspect.  The most significant was on the upper bowl of cry babys, ~5000′, ~200 m crown, 1-2 meters deep.  

1/23- Found fresh debris in a gully off point 3848′ behind the airport.  D2, ran ~2000′.

~ 1/10- There have been several natural windslabs that have released in the Thompson Pass region:

-South slope of catchers mitt, near 27 mile icefall,~3500′, ~300m wide ,~3′ deep, ran 500′ HS-N-R3-D2.5.  Photo shows extent of crown, which may have been bigger and is now filled in by wind transported snow.

– Gully Between Little and Big Oddessey, NW, 4000′, ~60 M wide, ~2-4′ crown, ran 1000′

-Averys, ~4000′, SW, ~70 M wide, ran ~1000′

1/11- Two natural wind slab avalanches observed at moonlight basin, 2500′-2800′, S aspect.  

The first was on the small last roll before the road and had debris chunks up to 3′ deep “crown filled in by wind”, 200′ wide.

The second was in a cross loaded gully ~ 300′ above the road, with a crown up to ~10′ deep, ~100′ wide.




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`      24 F         7 F

Temp at 3000`      18 F         14 F

Chance of precip   80%          40%

Precip amount
(above 1000 FT)    0.08 in      0.04 in

Snow amount
(above 1000 FT)    1 in         trace

Snow level         sea level    sea level

Wind 3000` ridges  E 5-10 mph   E 5-10 mph

  24h snowfall (inches) HN24W (inches)* Hi Temp (F) Low Temp (F) February snowfall Season Snowfall Snow height 
Valdez 1 .18 36 24 45 152 62
46 mile Trace 0 35 22 30 91 31

Thompson Pass “DOT”

5 .64 26 16 108 465

 HN24W= total water received last 24 hours in inches

Thompson Pass weather history 19/20 season beginning 12/21 through 1/23.  Click on links below to see full size image.






























TP Jan 2020

TP wx chart through 2/19


Additional Information

Our area has received up to 4′ of snow with strong south east- south west winds, and warm temperatures since 2/17.  This storm has been a great test of weak layers in our snowpack.  Reduced visibilities have prevented much in the way of observation of natural avalanche activity other than paths that either hit the road or got close to it.   Two paths on Three pigs with a south east aspect at 42 mile ran to the middle of their aprons and the lower north aspect slopes of RFS buried the highway under 10 feet of snow for ~150′ at 33 mile.   It is very likely that many other natural avalanches occurred on 2/19 and 2/20.  Crowns have been refilling and may make seeing previous naturals difficult once skies clear.

In areas that have received natural avalanches old instabilities will have been flushed out.  In areas that did not slide weak layers deep in the snowpack still exist.  These weak layers will be difficult to affect due to their depth, but would produce very large avalanches if triggered.  

The amount of new snow that we have received is sufficient to produce large avalanches that fail at the new snow/old snow interface.  The new snow will need time to properly bond to the underlying snowpack.  This bonding process will take time and large human triggered avalanches will be likely in the meantime.  As you venture out into the mountains for the first time after this storm terrain progression will be a very important tool to utilize.  Test small slopes with no consequence to assess snow stability before moving out onto steeper slopes.

Forecast Confidence is Moderate.

Resolution is Low 


 There have been limited observations from interior locations due to low snow at lower elevations.   Use caution if you travel in these areas.

If you see something in the mountains that could contribute to this forecast, leave a public observation.  The more observations we receive, the better we can tune our forecast. If you would rather not post an observation publicly, feel free to send me an email at [email protected]

Be aware that the elevation bands have changed on our website.  Low is now below 2000′, Mid is 2000-4000′ and high is 4000′ and above. 

Send in your best mountain recreation photos to [email protected] so we can post a photo of the week!

Photo of the Week

Thanks to Spencer Byson for sending in this photo!


The avalanche hazard is Considerable at all elevations.  Thompson pass has received 48 inches of snow, 5.6 inches of SWE and strong SE-SW winds from storms beginning on the 17th.  As temperatures slowly cool, winds relax and snowfall rates slow down, our snowpack will be adjusting to its’ new snow load.  During this adjustment phase human triggered avalanches will remain likely on slopes steeper than 30° and natural avalanches are still possible.  Avoid slopes steeper than 30° and terrain traps.