Storm slab cycle in the southern Whitefish Range

Location Name: 
Forecaster Observation - Canyon Creek, Whitefish Range
Observation date: 
Wednesday, December 12, 2018 - 14:45
Is this an Avalanche Observation: 
Yes
Observation made by: Forecaster

Location

Tabs

Quick Observation
  • A natural storm slab avalanche cycle occurred on sunny and shaded aspects at mid-elevations Tuesday night/Wednesday morning.  Most of the slides ran early in the storm and were covered with 6"+ of new snow. Slides failed approximately 1 foot below the surface at the new snow/old snow interface. Slides were mostly small D 1-1.5 with several D2.
  • New snow, up to 12" in depth, was dense and overloaded the well advertised weak surface snow. Textbook!
  • The snowpack was reactive to my weight with a number of shooting cracks (up to 20'+) and collapses.
  • Substantial wind transport occurred at mid and upper elevations throughout the day.
Snowpack, Avalanche, Weather Images: 
Travel Details
Region: 
Whitefish Range - Southern (south of Coal Creek)
Route Description: 

East of the ski area

Snowpack Details
Snowpack and Weather Details: 
Hide Terrain
Elevation of observation: 
5000-6500 ft
Above 6500 ft
Aspect(s) of observation: 
N
NE
E
S
Red Flags: 
Shooting cracks
Collapsing / whumpfing noises
More than a foot of new snow or heavy snowfall rates (>1"/hr)
Blowing snow
Persistent Weak Layers: 
Surface Hoar
Facets or Faceted Crust
On the surface
Buried
New Snow in the past 24 hours: 
12.00in.
Total Snow Depth: 
30
Blowing Snow: 
Moderate
Wind Speed: 
Moderate (Small trees sway)
Wind Direction: 
Southwest
Air temperature: 
Below Freezing
Snow line: 
2000
Sky Cover: 
Overcast (OVC)
Avalanche Details
Avalanche Details: 
Date and Time of Avalanche: 
Wednesday, December 12, 2018 - 01:45
Avalanche Type: 
Soft Slab
Failure Plane/Weak Layer: 
New/old snow interface
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Trigger: 
natural
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Start Zone Slope Angle: 
35
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Destructive Size: 
D1.5
Relative Size: 
R2 Small
Crown Height: 
1 ft
Avalanche Length (Vertical Run): 
100ft.
Avalanche Width (Average width): 
50ft.
Avalanche Location: 
Date and Time of Avalanche: 
Wednesday, December 12, 2018 - 20:30
Avalanche Type: 
Soft Slab
Failure Plane/Weak Layer: 
New/old snow interface
Hide Trigger
Trigger: 
natural
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Start Zone Slope Angle: 
35
Aspect: 
South
Starting Elevation: 
above-treeline
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Destructive Size: 
D2 Could bury, injure, or kill a person.
Relative Size: 
R2 Small
Crown Height: 
1 ft
Avalanche Length (Vertical Run): 
500ft.
Avalanche Width (Average width): 
100ft.
Avalanche Location: 
Date and Time of Avalanche: 
Wednesday, December 12, 2018 - 20:45
Avalanche Type: 
Soft Slab
Failure Plane/Weak Layer: 
New/old snow interface
Hide Trigger
Trigger: 
natural
Hide Terrain
Start Zone Slope Angle: 
35
Aspect: 
East
Starting Elevation: 
above-treeline
Hide Size
Destructive Size: 
D2 Could bury, injure, or kill a person.
Relative Size: 
R2 Small
Crown Height: 
1 ft
Avalanche Length (Vertical Run): 
200ft.
Avalanche Width (Average width): 
150ft.
Avalanche Location: