Weak basal facets exist at the ground which have shown propagation energy in stability tests as recently as 11/30. Our area saw a significant natural avalanche cycle 12/1-12/2 due to intense snowfall and rising temperature. For details, see avalanche activity section. Although the hazard has significantly decreased from a few days ago, it is important to keep in mind that trigger points may exist in isolated locations such as near rock outcroppings. Anywhere the snowpack is thinner than the surrounding area is a point of weakness. This avalanche problem will likely not show any signs of instability and is very difficult to predict and assess. The best way to deal with a deep slab problem is to give it time and avoid dangerous avalanche terrain. Avoid large avalanche slopes, thin rocky areas and unsupported terrain. Previous skier’s tracks are not a sign of stability.
We are just 24 hours past a storm that has deposited 10″ of water and 90″ of snow at Thompson Pass in a 7 day period. This storm left with decreasing temperatures and is “right side up” above 3000′. Density changes within the storm snow may act as failure planes on specific terrain features like steep convex roll overs or unsupported terrain.
12/3- Numerous natural avalanches were observed north of Thompson Pass with many avalanches failing at the ground. Clouds prevented a complete picture of the activity. 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 the Shovel approach gully 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.
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. Starting zones were obscured by clouds.
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
12/4- Clearing skies and light north winds.
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` 21 F 1-7 F
Temp at 3000` 8-14 F 2-10 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 8-15 mph NE 10-18 mph
Thompson Pass weather history 20/21. Click on links below the images to see full size view
TP NOV as of 11/18
The avalanche hazard is Moderate at mid and upper elevations. Human triggered avalanches are possible. Heightened avalanche conditions may exist in specific locations, such as thin rocky areas where it is possible to affect weak, faceted layers at the bottom of our snowpack and trigger a deep slab. Deep slabs are difficult to predict, and if triggered and caught are generally unsurvivable. Tracks are not a sign of stability with a deep slab problem. Today will be the first sunny day after a major storm cycle, be conservative with terrain choice and live to ride another day.
The hazard will rise throughout the day if the wind is stronger than forecasted and begins to redistribute the new snow.
For more information click the (+full forecast) button below.
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