Blue-bird, calm winds, and variable conditions

Location Name: 
Forecaster Observation - Ousel Peak to Skiumah Lake, Flathead Range
Observation date: 
Monday, February 12, 2018 - 13:00

Is this an Avalanche Observation: 
Yes
Observation made by: Forecaster

Location

Tabs

Quick Observation

Ski traversed the northern portion of the Flathead Range to evaluate recent wind-effect and the remnants of last week's deep slab cycle across multiple basins.

  • Perfect day for a long traverse at upper elevations
  • Found evidence of wind-effect throughout our tour to ridgelines, prominent gullies extending down from ridgelines, and in upper portion of basins
  • Wind-effect was most evident at upper and mid elevations on northwest to northeast aspects
  • Numerous natural, small wind-slab avalanches noted on northwest to northeast aspects originating directly below large cornices
  • Wind-protected slopes harbored 6-10" of low density snow at mid and upper elevations
  • Temperatures remained cold throughout the day and we didn't observe surface warming lending to instability in the surface snow on sunny aspects
  • Skiumah Creek provided the only remnants of our last deep slab cycle with several D2's, one D3, and one D3.5 deep slab avalanche most likely occurring on Thursday or Thursday night
  • No large crown lines or debris piles noted in basins north of Skiumah Creek
Snowpack, Avalanche, Weather Images: 
Travel Details
Region: 
Flathead Range - Middle Fork Corridor
Route Description: 

Skied from Ousel Peak to Skiumah Lake, then out Skiumah trail to highway 2.

Activity: 
Skiing
Snowpack Details
Snowpack and Weather Details: 
Hide Terrain
Elevation of observation: 
3500-5000 ft
5000-6500 ft
Above 6500 ft
Aspect(s) of observation: 
N
NE
E
SE
S
SW
W
NW
Persistent Weak Layers: 
On the surface
New Snow in the past 24 hours: 
0.00in.
More comments about the snowpack and weather: 
Surface conditions on all wind-exposed slopes was a mixture of a stiff wind-slab or a thin wind-skin, while in wind-sheltered terrain we found 6-10" of low density snow. Widespread surface faceting was observed on top of wind-stiffened snow primarily on shady aspects (northwest to northeast), while not as prominent on sunny aspects with similar wind-effect. Low density snow on shady aspects (northwest to northeast) in wind-sheltered terrain was becoming unconsolidated with minor sluffing noted in steeper terrain, but not running long distances. Snow surface on sunny, wind-sheltered slopes was more consolidated than shady aspects, but cold temperatures didn't contribute to warming instabilities on those slopes. 3400'-6000' consisted of a breakable rain crust below low density snow. From 6000'-6200', rain crust was thin and hardly noticeable below low density snow and nonexistent above 6200'. We observed cracking below our skis in recently formed wind-slabs on primarily northwest through northeast aspects. Using small test slopes to evaluate sensitivity of wind slabs did not produce propagating cracks outwards.
Avalanche Details
Avalanche Details: 
Date and Time of Avalanche: 
Thursday, February 8, 2018 - 23:00
Avalanche Type: 
Hard Slab
Failure Plane/Weak Layer: 
Unknown
More information or comments about the avalanche: 

Lighting was poor to get good picture from Skiumah Lake, but multiple large crows were visible and a portion of slope below ridgeline slide to the ground.

Hide Trigger
Trigger: 
natural
Hide Terrain
Aspect: 
Northeast
Starting Elevation: 
above-treeline
Hide Size
Destructive Size: 
D3.5
Relative Size: 
R4 Large
Avalanche Length (Vertical Run): 
2600ft.
Avalanche Width (Average width): 
1000ft.
Hide People Involved
Number of people caught: 
0
Avalanche Location: 
Date and Time of Avalanche: 
Thursday, February 8, 2018 - 23:00
Avalanche Type: 
Hard Slab
Failure Plane/Weak Layer: 
Unknown
Hide Trigger
Trigger: 
natural
Hide Terrain
Aspect: 
North
Starting Elevation: 
above-treeline
Hide Size
Destructive Size: 
D3 - Could destroy a car, a wood house, or snap trees
Relative Size: 
R3 Medium
Avalanche Length (Vertical Run): 
1400ft.
Avalanche Width (Average width): 
500ft.
Hide People Involved
Number of people caught: 
0
Avalanche Location: 
Date and Time of Avalanche: 
Thursday, February 8, 2018 - 23:00
Avalanche Type: 
Hard Slab
Failure Plane/Weak Layer: 
Old snow
Hide Trigger
Trigger: 
natural
Hide Terrain
Aspect: 
North
Starting Elevation: 
near-treeline
Hide Size
Destructive Size: 
D2 Could bury, injure, or kill a person.
Relative Size: 
R3 Medium
Avalanche Length (Vertical Run): 
500ft.
Avalanche Width (Average width): 
200ft.
Hide People Involved
Number of people caught: 
0
Avalanche Location: 
Date and Time of Avalanche: 
Sunday, February 11, 2018 - 12:00
Avalanche Type: 
Hard Slab
Failure Plane/Weak Layer: 
Within storm snow
More information or comments about the avalanche: 

Multiple natural wind-slabs observed on northwest to northeast aspects.

Hide Trigger
Trigger: 
natural
Hide Terrain
Starting Elevation: 
above-treeline
Hide Size
Destructive Size: 
D1 Relatively harmless to people.
Relative Size: 
R2 Small
Crown Height: 
Less than 1 ft
Avalanche Length (Vertical Run): 
200ft.
Avalanche Width (Average width): 
50ft.
Hide People Involved
Number of people caught: 
0