3/11: 2 Human triggered avalanches observed on the Thompson Pass corridor.
Skier triggered avalanche in Nicks Happy Valley. Skier was traversing the wind loaded northwest aspect of the gully and released a slab ~1 foot deep and 100′ wide, ran ~150 vertical feet to the bottom of the gully. SS-ASu-D1.5-I.
3/5: -Natural D 2.5 occurred on the NW aspect shoulder of the Python Buttress “Ptarmigan Drop” milepost 31. Avalanche crown was reported to be 10-15 feet deep by DOT and ran to the ground. Crown was quickly filled back in by intense snow transport.
3/4: A natural D3 avalanche ran above the 37 mile tsaina bridge. South aspect ~5500′, stepped down multiple times, ran to the ground in places. The main debris fell short of the highway, mature uprooted trees 6-12 inches in diameter were thrown onto the road by powder blast.
-The gully downstream of Bridal Veil Falls produced a large avalanche, D2.5, that buried the river with over 10′ of debris, the powder blast pushed sticks into the parking lot on the other side of the road.
3/3: DOT mitigation work produced another large avalanche that affected the Richardson Highway at ~ mile 39. Initial reports stated that the avalanche buried the highway under 15 feet of debris for ~500 feet.
2/28: Natural wind slab avalanche 4000′. N-HS-R2-D2, West aspect slope that descends from Crudbuster basin into IguanaBacks. Stepped down immediately below initial crown, to the ground in places.
2/26: Large natural observed at 48 mile off Point 5064 (Stuart). N-HS-R3-D3, N-W aspects. Observed from the highway. Looked fresh, probably within the last 24 hours. Appears to have released from a N aspect bowl ~40-45° at~4500′, then stepped down and wrapped around the corner onto NW-W aspects. Crown on step down is estimated to be over 3 meters deep in places. Couldn’t see extent of track length. Crown was over 1/2 mile wide. 3 small, sympathetic pockets were observed over 1/2 mile away in moderate terrain with crowns ~1-2 meters. Picture taken from over 3 miles away.
2/24: Natural avalanche observed on the north face of Goodwills’ ~5500′, D-2.5, 200-300′ wide. Ran to the bottom of the slope ~600′, crown ~5′ deep.
2/23: – Natural avalanches D2-2.5 on the east face of Mt. Tiekel were observed.
2/21: Multiple natural and human triggered avalanches were observed 2/21.
Debris along the highway after DOT cleanup work.
Debris that over ran the highway and was deposited into the Tsaina Gorge.
Natural near the toe of the Worthington Glacier.
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. These slides ran into the flat ~800 vertical feet. Slides were triggered by DOT mitigation work 2/19.
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 Highway 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 MP 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 (Promised 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. 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′.
Photo of 1st remote trigger listed
-Natural avalanches observed on south aspect at MP 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 Crybaby’s, ~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.
3/12: Northeast winds will increase during the morning hours before dying off this evening. Wind gusts to 75 mph are forecasted for 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` 18 F 8 F
Temp at 3000` -5 to +4 F 4-18 F
Chance of precip 0% 0%
(above 1000 FT) 0.00 in 0.00 in
(above 1000 FT) 0 in 0 in
Snow level sea level sea level
Wind 3000` ridges NE 25-55 mph NE 20-45 mph
Thompson Pass “DOT”
HN24W= total water received last 24 hours in inches
Thompson Pass weather history 19/20 season beginning 12/21. Click on links below to see full size image.
TP DEC 19
TP Jan 2020
TP WX chart February 2020
TP WX chart through 3/5
Very cold and dry conditions in January created a weak faceted snowpack. The effect of this weather was more pronounced on the north side of Thompson Pass, where temperatures were colder and the snowpack was thinner.
The Valdez/Thompson Pass area has received fairly regular snow storms since late January with strong outflow winds following every storm. These wind events have redistributed the snow and created a snowpack with a high degree of spatial variability.
On 3/1, our area received 2 feet of low density snow that was quickly followed by our strongest wind event of the season, with wind gusts reaching 106 mph. On 3/5, during the peak of wind intensity, numerous natural avalanches released north of Milepost 31. Many of these slides stepped down to the ground. This shows us that deep persistent weak layers, formed during the January cold snap, still exist in our intermountain and continental zones. Wind slabs created 3/4-3/6 have gained strength and consist of a variety of very hard surfaces. These surfaces will likely act as a bed surface for subsequent storms.
New windslabs created 3/5 will make affecting deeper layers in the snowpack more difficult. Although these layers deep within the snowpack may be more difficult to affect, they are not gone. Once temperatures warm up in the spring, watch for these deep layers to “wake up” and produce very large, dangerous avalanches.
3/7-3/12: Our area has received 6-12 inches of new snow. Winds have ramped up once again 3/10 and have created another layer of wind slab on lee aspects. These have remained reactive in specific locations, which include the lee side of terrain features. 2 human triggered avalanches were noted 3/11 on the Thompson Pass corridor.
Forecast Confidence is Moderate.
Resolution is Low
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]
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 shredding in this photo!
The avalanche hazard is considerable at mid and upper elevations. Wind speeds reached 80mph on Thompson Pass the night of 3/10. These strong winds have formed a fresh layer of windslab 1-2 feet deep on lee aspects (SE-NW). Winds will once again be very strong on Thompson Pass 3/12, with gusts forecasted to reach 75 mph. New windslabs need to be given time to gain strength, in the meantime human triggered avalanches will be likely today on recently wind loaded slopes steeper than 30°. Avoid cross loaded gullies, upper elevation start paths that have received top loading and terrain traps.
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