Valdez

Forecast Expired - 12/18/2020

Above 3,000ftModerate

1,500 to 3,000ftModerate

Below 1,500ftLow

Degrees of Avalanche Danger

Low
Moderate
Considerable
High
Extreme

Avalanche Problems

Problem 1

Wind Slab:

Light snow has been falling on Thompson Pass the last few days with 4″ of accumulation in the last 72 hours and moderate northeast winds.  Shallow, soft wind slabs were observed near Thompson Pass 12/15.  These were small but reactive.  It may be possible to trigger a wind slab avalanche around 6″ -12″ deep on the lee side of ridge lines and in cross loaded gullies.  Wind has been less significant north of Thompson Pass which makes this hazard less likely in those locations.  This hazard will increase late in the day.  Winds are forecasted to increase to 50 mph combined with snowfall.  This will allow wind slabs to become deeper and more sensitive.

Likelihood:

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

Size:

  • Historic
  • Very Large
  • Large
  • Small

Trend

  • Increasing
  • Steady
  • Decreasing

Avalanche Activity

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

 

 

 

Weather

12/17-

...WINTER STORM WATCH REMAINS IN EFFECT FROM THIS EVENING THROUGH
FRIDAY AFTERNOON THROUGH THOMPSON PASS...

* WHAT...Blizzard conditions possible. Total snow accumulations of
  5 to 10 inches possible. Winds could gust as high as 50 mph.
  Widespread blowing snow could reduce visibilities to a quarter
  mile or less.

* WHERE...Thompson Pass.

* WHEN...From this evening through Friday afternoon.

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
management.

                   Today        Tonight

Temp at 1000`      21 F         14 F

Temp at 3000`      9-17 F       4-11 F

Chance of precip   30%          70%

Precip amount
(above 1000 FT)    0.03 in      0.22 in

Snow amount
(above 1000 FT)    trace        2-5 in

Snow level         sea level    sea level

Wind 3000` ridges   NE 3-38 mph NE 6-41 mph. Gusts to 50 mph developing.

Remarks...A Winter Storm Watch for possible blizzard conditions
remains in effect from this evening through Friday afternoon.
Date: 12/16 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 Trace 0 29 19 .24 14 62 31
Thompson Pass N/O N/O 10 3 .04 48 181 50
46 Mile Trace 0 18 2 ~ 23 52 22

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

 

November 2020

TP as of 12/14

 

 

 

 

 

 

 

 

 

Additional Information

 

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′. 

 

Announcements

The avalanche hazard is moderate at mid and upper elevations.  Human triggered wind slab avalanches 6-12″ deep are possible on the lee side of terrain features and just below ridge lines.  The area in the immediate vicinity of Thompson Pass will be the most likely to see this hazard present.   Use small test slopes to determine if fresh wind slab is present in the area that you choose to travel.  Avoid terrain traps were even small wind slabs could bury a person deeply.  The hazard will be lower were the new snow is unaffected by wind.  The hazard will be increasing later in the day as a storm approaches that will ramp up north winds to 50 mph on Thompson Pass.

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

Your observations are valuable!   If you have been out recreating in the mountains, please leave an observation.