Storm slab cycle in Cascade Creek

Location Name: 
Forecaster Observation - Cascade Creek, Flathead Range
Observation date: 
Thursday, February 14, 2019 - 18:15
Is this an Avalanche Observation: 
Yes
Observation made by: Public

Tabs

Quick Observation

Found a quiet snowpack in the wake of a widespread storm slab cycle yesterday. 

  • We found the 2+ feet of storm snow from the past few days produced a widespread storm slab cycle on Wednesday morning in Cascade Creek.  Crowns were 12-18" thick, and produced large (D2) debris piles.  There was evidence of similar activity in Skiumah and Rescue Creeks, at least D2 in size.  Storm instabilities appeared to be healing quickly...the recent snow felt right-side up today and did not produce any signs of instability.  
  • We noted one larger slab avalanche, estimated 3 to 4 feet deep, that was either a persistent slab or just a heavily wind loaded storm instability in alpine terrain.  It looked like one of the storm slabs in Cascade also stepped down to the GroundHog crust around 5,200', but the difference in slab height is relatively minor at that elevation.   The GH crust did not produce any signs of instability today except a couple localized collapses at low elevations.  
  • We generally felt comfortable skiing steep terrain because most everything had flushed in this drainage.  We would have been cautious of slopes still holding the full storm's snowpack on them, mostly due to uncertainty around the GroundHog crust.  This interface was down 3.5' deep at 6,400'.  
  • We found small grained surface hoar on the surface from when we emerged to open slopes at 5500' to our turnaround at 6,400'.  Wind was transporting snow on high peaks.  
Snowpack, Avalanche, Weather Images: 
Travel Details
Region: 
Flathead Range - Middle Fork Corridor
Route Description: 

Cascade Creek to 6400'

Activity: 
Skiing
Snowpack Details
Snowpack and Weather Details: 
Hide Terrain
Elevation of observation: 
3500-5000 ft
5000-6500 ft
Aspect(s) of observation: 
N
NE
Red Flags: 
More than a foot of new snow or heavy snowfall rates (>1"/hr)
Persistent Weak Layers: 
Surface Hoar
Facets or Faceted Crust
On the surface
Buried
More comments about the snowpack and weather: 
No wind where we were. Could see blowing snow off of high peaks from SE winds. Good views of Nyack and parts of Skiumah Basin and no deep slab avalanches, most storm slab crowns were already blown over by snow and wind, just debris piles visible. One pit a 4500', NE aspect: ECTN on facets above 2/2 crust, down 70 cm.
Blowing Snow: 
None
Wind Speed: 
Light (Twigs in motion)
Wind Direction: 
Southeast
Highest Precipitation Rate: 
No Precipitation (NO)
Avalanche Details
Avalanche Details: 
Date and Time of Avalanche: 
Wednesday, February 13, 2019 - 06:15
Avalanche Type: 
Soft Slab
Failure Plane/Weak Layer: 
Within storm snow
More information or comments about the avalanche: 

Various aspects, mid elevations. Likely upper elevations too but crowns were obscured by subsequent wind.

Hide Trigger
Trigger: 
natural
Hide Terrain
Starting Elevation: 
near-treeline
Hide Size
Destructive Size: 
D2 Could bury, injure, or kill a person.
Relative Size: 
R2 Small
Crown Height: 
1 ft
Avalanche Location: 
Date and Time of Avalanche: 
Thursday, February 14, 2019 - 18:45
Avalanche Type: 
Soft Slab
Failure Plane/Weak Layer: 
Unknown
More information or comments about the avalanche: 

Observed from a long distance away. Looked like it could be a PS on the 2/2 suncrust, but not sure.  Couldn't see the runout but assume it ran most of the track and was around D3 in size. 

Hide Trigger
Trigger: 
natural
Hide Terrain
Aspect: 
Southeast
Starting Elevation: 
above-treeline
Hide Size
Destructive Size: 
D3 - Could destroy a car, a wood house, or snap trees
Relative Size: 
R3 Medium
Crown Height: 
3 ft
Avalanche Length (Vertical Run): 
2400ft.
Avalanche Width (Average width): 
200ft.
Avalanche Location: