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.
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` 27 F 22 F
Temp at 3000` 25 F 25 F
Chance of precip 100% 80%
(above 1000 FT) 0.13 in 0.10 in
(above 1000 FT) 2-4 in 1-3 in
Snow level sea level sea level
Wind 3000` ridges E 10-30 mph E 5-25 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
An outflow wind event began the night of 3/3 with wind speeds reaching 106 mph the night of 2/4 on Thompson Pass. These strong winds kicked off a fairly significant natural avalanche cycle. Most of the activity that we saw was north of mile post 31, with multiple step downs that reached the ground. Numerous windslabs were observed on Thompson Pass, but with no observed step downs. Little activity was observed in coastal areas, although crowns were filling in rapidly with wind transported snow. The distribution with this avalanche cycle gives some insight on the strength of snowpacks for different areas. Stronger snowpacks exist towards the coast, with decreasing strength as you move north. Step downs to the ground in our continental zone is a big RED FLAG. This indicates that deep persistent weak layers are present that have the potential to create very large avalanches.
Storm totals for the 3/1 storm were 24 inches in Valdez and 20 inches on Thompson Pass. This new snow was fairly dry and uncohesive, which will make it especially susceptible to redistribution into wind slabs by strong outflow winds.
Strong northeast winds affected our area beginning 2/23, building wind slabs and further stressing weak layers deep within our snowpack. Numerous natural avalanches have occurred since 2/19. Most of these have happened north of milepost 32.
Since 2/17, our area has received up to 4′ of snow with strong southeast-southwest winds.
This new snow fell on a spatially variable snowpack. Some areas have very poor structure with problem layers buried deep within the snowpack. Other areas do not have this problem. Generally, weaker snowpacks have been found the further you move north from Thompson Pass.
In areas that did not slide 2/19-2/23, 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, deadly avalanches if triggered.
Forecast Confidence is High.
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]
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 moderate at all elevations. It is still possible to trigger windslab avalanches 1-3 plus feet deep in specific location. These locations include top loaded slopes and cross loaded gullies on SE-NW aspects. Avalanches triggered in the upper snowpack have the potential to step down to deeper layers in the snowpack and create very large avalanches. Avoid large start zones above 30° and terrain traps.
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