The latest snow storm on 2/17 favored coastal areas, delivering 18 inch storm totals to Valdez with 4-8 inches on Thompson Pass. This new snow has been redistributed onto lee aspects (SE-NW) by strong northeast winds in some locations. As noted in the bottom line statement, winds were widespread 2/19, with drifting observed at valley floor locations that are generally calm during wind events. This may create wind slabs further down slopes than is typical. In addition to widespread winds, a smooth bed surface is in place in most locations which will give avalanches a slick surface to run on. Although wind slabs will likely be less than a foot deep, these can still be dangerous above terrain traps or in areas where being knocked off your feet would have consequences.
The Port of Valdez will be a different story as there is significant snow available for transport and deep wind slabs of 2-3 feet could be forming on the lee side of ridges and in cross loaded terrain.
Avoid terrain traps, large avalanche paths and unsupported terrain in the Intermountain and Continental zones. Avoid all wind loaded slopes steeper than 32° in the Maritime climate zone.
Human triggered wind slab avalanches my be able to step down to the layer below the 2/1 wind slab. This would likely occur in an area where the old wind slab is thinner thus easier to affect layers beneath it. In this scenario more destructive hard slab avalanches would be the outcome.
Faceted snow has been observed beneath these wind slabs in multiple locations and climate zones and has showed propagation energy as recently as 2/18. These faceted layers are difficult to affect due to the very hard (pencil) 6-12 inches of wind slab that exists above them, but would carry significant consequences if affected. Use caution in areas where you find this layer to be thinner and/or punchy.
Instabilities in the lower snowpack exist in some locations. Several full depth avalanches have occurred in our area as recently as 1/26. Locations include Billy Mitchell, 40.5 mile peak, Nicks Buttress, East face of Mt. Dimond and the SW face of Acapulco. It is unclear as to wether Acapuulco was full depth, but it was nevertheless a massive avalanche. A natural full depth avalanche at 40.5 Mile Peak was the most recent, ~6000′ NW aspect, and is a clear indicator that basal facets are still a concern in our continental and intermountain zone. This avalanche likely failed during the 1/26 wind event, potentially initiated by cornice fall. See avalanche activity section for photo
Although it is very unlikely to make an avalanche on these layers they would be unsurvivable. Avoid traveling under cornices and avoid avalanche terrain during rapidly changing weather.
2/17- A D 2 natural was observed off steep north facing terrain on Benzene peak that ran 800′. Several small natural D1’s were observed in Benzene Alley on convex terrain features. These all ran on the 2/1 wind board.
2/13- No natural or human triggered avalanches have been observed or reported since 2/1. Thompson Pass has received only 1 inch of SWE in the last 3 weeks.
2/1- Natural avalanches from the 2/1 outflow event were noted on Hippie Ridge in cross loaded gullies SW aspect/ D2’s ~4000’/ depths were difficult to gauge because crown were rapidly being filled in by wind deposit.
-Slides were also noted on Averys: SW/~3500’/ ~300′ wide/ D2
40.5 Mile Peak:W-N/~3500’/ 3 separate D2’s/ ~200-300′ wide
As stated above depths were difficult to gauge due to wind refill. A report did come in of 3′ crowns on the west aspects of the Mt. Dimond moraines/ ~4000’/ ~300′ wide
Many other avalanches likely occurred but observation was limited due to wind refilling crowns.
1/27- The photo below shows a natural D3 avalanche that was reported on 1/30. It is uncertain when this avalanche occurred. It most likely happened during the 1/26 wind event. 40.5 Mile Peak/ NW aspect/ full depth, 3+ meters / ~800′ wide/6000′. Demonstrates that basal facets are still a player in our continental zone.
-Natural D2 avalanche observed at 42 mile in a cross loaded south facing gully.
1/18-19- Numerous wet loose slides occurred region-wide below 2000′.
Schoolbus had a natural avalanche affect the highway early 1/19 that covered the road with 2′ of debris for ~100′.
DOT mitigation efforts produced avalanches at Snow Slide Gulch, Ptarmigan Drop (Nick’s Buttress), Python Buttress, Three Pigs and 40.5 Mile peak.
The most notable slide occurred at Ptarmigan Drop and Python and deposited 6′ of snow on the highway for 150′ of road length. Crowns failed at ~3500′ and were extensive, connecting almost the entirety of the Nicks’ through Python Buttresses. The western extent of Nicks stepped down to the ground in an area that failed full depth 12/1. Nearly a mile of terrain was effected with some crowns approaching a quarter mile in length.
It is unclear how much of the activity at Three Pigs and 40.5 Mile was natural versus artillery triggered, but there were multiple paths leaving debris at the bottom of run outs.
1/15- Two natural D2 avalanches observed on a NW aspect of RFS, crown~ 3′ deep.
1/9- Natural avalanche observed on an east aspect of North Tiekel. Likely failed during warmup the night of 1/8. Avalanches failed at terrain convexities around 3500′. This area is 4 miles north (beyond) our Continental forecast zone, but is still indicative of that zone.
1/8- 3 separate skier triggered avalanches on Cracked Ice at 2800’/ 40 cms deep (16 inches)/ 100-300′ wide/ ran 600-700 feet and failed on the 1/3 buried surface hoar layer. SS-AR-U-D1.5-2-O
Lower section of far lookers left crown.
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.
– HS-N-R3-D3-G, NW Crudbusters/ ~5000′
-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
2/20- Cold and cloudy with windchills of -35 F possible on Thompson Pass.
The Thompson Pass Mountain Forecast covers the mountains (above
1000 ft) surrounding Keystone Canyon through Thompson Pass to
This forecast is for use in snow safety activities and emergency
Temp at 1000` 14 F 7 F
Temp at 3000` -3 to -15 F 4-13 F
Chance of precip 30% 30%
(above 1000 FT) 0.03 in 0.03 in
(above 1000 FT) trace trace
Snow level sea level sea level
Wind 3000` ridges NE 20-34 mph NE 20-34 mph
Remarks...Wind chills to -35 F possible this morning.
NRCS water survey results 2/4
Thompson Pass weather history 20/21. Click on links above the images to see full size view
TP DEC 2020
TP January 21
TP as of 2/11
Our season began with a cold, dry and windy November which promoted faceting in the thin snowpack that existed. Only 28 inches of snow were recorded at Thompson Pass from 11/1 through 11/24.
November 25 began a series of storms that deposited 90” of snow and 11.1” of SWE on Thompson Pass at road level in an 8 day period. At the tail end of these storms the pass received 25” of snow and 3.7” of SWE in 48 hours, along with rising temps that pushed freezing line up to 3000’. This sparked a widespread natural avalanche cycle that failed on faceted snow created in early November. Many of these slides failed at the ground. See avalanche activity section for pictures of the cycle.
December continued with fairly regular snow fall and a couple periods of stable (dry) weather, with snowfall totaling 120 inches on Thompson Pass. Another, smaller natural avalanche cycle occurred on the 12/22 after Thompson Pass received 44 inches of snow with 4” of SWE in a 4 day period. Two full-depth naturals occurred in the Continental region on NW-N aspects between 4500-5000’ on NW Crudbusters and Billy Mitchell. Various other soft slab D2’s occurred in other regions as well. This indicated that depth hoar is still a concern in the Continental region but is becoming less so in our Maritime and Intermountain regions. Incremental snowfall during the second half of December has allowed the snowpack to slowly gain depth and strength.
Cold, stable weather at the end of December created widespread areas of surface hoar up to 1 cm in height, observed on all aspects between 2000-4000’ and up to ridge lines in isolated locations. This layer was more concentrated on the north side of Thompson Pass, promoted by colder temperatures and an ice fog layer that was forming during this time frame. However, this surface hoar has been reported in the Port of Valdez up to brush line.
1-3 feet of snow has since accumulated on top of this weak layer from 1/3-1/17.
A significant change in weather arrived on 1/18 delivering as much as 5″ of water to low lying areas with over 2 feet of snow accumulating above 2000′ accompanied by strong southeast winds. This prompted a natural avalanche cycle with the mid elevation band seeing the most activity.
Outflow winds have begun to affect our area beginning 1/26. This event was not widespread with many areas remaining protected. A major outflow event with speeds up to 80 mph on 2/1 had a more widespread affect on our area than the 1/26 event. Windward slopes were scoured and hard wind slabs were built on lee aspects. Once the dust settled surface snow ranged from exposed ridges blown to ground, sastrugi and very hard wind slabs. Numerous small to moderate natural avalanches occurred during the event.
On 2/2 Thompson pass received a foot of 5% density snow (very low density). This new snow rests on a very hard bed surface and has been slow to bond. Numerous point releases and sluffs have been observed in terrain steeper than 35°.
On 2/9 our area received an additional 10-16 inches of 4 % density snow, this has added to the depth of snow that is resting upon a hard bed surface.
In areas that were protected from the 2/1 hurricane force winds a freezing fog crust exists 40 cms down, up to 5000′. Small facets are forming above and below this crust and may become a concern in the future…
In the time period 1/25-2/15 Thompson Pass has recieved ~1″ of SWE and Valdez ~.6″. This has caused faceted snow to form in our mid snowpack.
Our drought ended on 2/16 with the coast receiving 18 inches of new snow and Thompson Pass 6-10 inches.
Snowpack structure generally becomes thinner and weaker as you move north from Thompson Pass
Photos of Surface Hoar taken 1/1 on Crudbusters at 3500′ north aspect.
The avalanche hazard is Considerable at all elevations. Human triggered wind slab avalanches up to 1 foot in depth are likely today. In the Maritime climate zone wind slabs may reach depths of 2-3 feet due to significantly more snow being available for transport. Northeast winds were strong on 2/19 and widespread, with strong valley floor winds observed. Expect wind slabs to exist at all elevations. Keep in mind that even shallow wind slabs can be dangerous in terrain traps and exposed/extreme terrain. The hazard will be increasing with continued moderate winds today that will gain strength this evening.
For more information click the (+full forecast) button below.
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