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Glide avalanche on Snowshed
Location Name:
Southern Flathead Range
Observation date:
Tuesday, December 29, 2020 - 18:30
Is this an Avalanche Observation:
Yes
Observation made by:
Public
Tabs
Quick Observation
Toured up to the SE face of Snowshed Mtn to take a closer look at the recent glide avalanche.
The avalanche failed sometime after Christmas morning, estimating that night or next day?
Crown was located at about 7200’ elevation near the top of the path on a SE aspect, and was 1-4’ thick and about 500’ wide.
Debris terminus is uncertain, but saw what looked like debris at the bottom of the path near Sheep Creek (~3000’ vertical fall).
It appeared that the glide failure may have also sympathetically triggered additional slab(s) that appeared to fail on some other buried persistent weak layer in the mid-pack. Suspect the Dec 9th crust/facet layer given our assessment of the crown and a snow pit profile dug nearby.
No other avalanche activity observed.
We found about 5-15” of settled powder snow on top the Dec. 22nd crust depending on elevation during the tour. Around 6500’ this crust eventually disappeared.
Recent wind-loading was minimal with very little new wind slab development at all elevations we travelled through.
Snow profile conducted at 7100’ on an easterly aspect and about 30 m from the crown of the glide avalanche mentioned above. The Dec 9th crust/facet combo was about 2’ below the surface. Propagation with hard force during an Extended Column Test (see pit profile) on a thin layer of facets resting atop the Dec. 9th crust.
No shooting cracks, audible collapses, or any other signs of instability during the ski tour.
Skies mostly obscured by fog, but occasional lifting allowed for some better visibility at times.
Very light snow coming down as on again/off again showers with trace accumulations over the day.
Light and variable winds at all elevations.
Daytime high air temperatures reached the mid-20s °F on the Canyon Floor but only the mid-teens or single digits °F at elevations above 6000’.
Snowpack, Avalanche, Weather Images:
Travel Details
Region:
Flathead Range - Middle Fork Corridor
Activity:
Skiing
Avalanche Details
Avalanche Details:
Date and Time of Avalanche:
Saturday, December 26, 2020 - 06:30
Number of avalanches:
1
Avalanche Type:
Glide
Failure Plane/Weak Layer:
Ground
Trigger
Trigger:
natural
Terrain
Aspect:
Southeast
Starting Elevation:
7200
Size
Destructive Size:
D3 - Could destroy a car, a wood house, or snap trees
Relative Size:
R3 Medium
Crown Height:
3 ft
Avalanche Width (Average width):
500ft.
Avalanche Location:
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