Wind affected Swan Range

Location Name: 
Forecaster Observation - Noisy Basin, Swan Range
Observation date: 
Friday, February 23, 2018 - 14:00

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

Location

Tabs

Quick Observation

Toured into the Swan Range to look at the snow surface prior to this weekends storm.

  • Last weekends blizzard affected most slopes and aspects at upper elevations. East aspects were scoured with a windboard layer that was 2-6" thick and 1F hard.  This layer varied between supportable and unsupportable making for exciting skiing. At upper elevations, the surface snow was completely stripped away revealing the 2/8 rain crust which was 1/2" thick. West aspects had a 6-12" 1F wind slab that thinned as you decreased elevation. Most sheltered locations were wind affected with a few heavily treed areas maintaining powder conditions.
  • Visibility was poor but we did notice one storm slab avalanche at 6000' on a north aspect in the forest. This slab was 18' thick and 30' wide with the bed surface being the 2/8 rain crust.
  • Recreationalists whom we spoke with reported a "small" storm slab avalanche mid-slope on Crown Bowl with a west aspect. They also noted a possible glide crack on the same face of Crown Bowl. Both observations were from Friday during bluebird conditions.
  • Despite limited snow for transport fresh cornice formation was occurring from southwest winds. 
  • 1-2" of low density (5%) snow fell during our tour.
  • No signs of instability noted except for small fresh cornices that we were able to easily break.
Snowpack, Avalanche, Weather Images: 
Snowpack, Avalanche, Weather Videos: 

February 23, 2018 - Wind affect in the Swan

Travel Details
Region: 
Swan Range - West Side (Flathead Valley access)
Route Description: 

Up the Noisy Basin road to Camp Misery. We traveled from there to the ridgeline south of Camp Misery. Visibility was about zero on the ridge and we ended our tour there.

Snowpack Details
Snowpack and Weather Details: 
Hide Terrain
Elevation of observation: 
5000-6500 ft
Above 6500 ft
Aspect(s) of observation: 
N
NE
E
SE
Persistent Weak Layers: 
Not observed
New Snow in the past 24 hours: 
0.00in.
More comments about the snowpack and weather: 
We did not dig a pit. Instead, we focused on collecting surface snowpack data on a variety of aspects. We felt this information was much more important due to the storm that is forecast for the weekend. In most locations, the surface wind affected snow was not bonding well to the underlying low-density snow. We determined this through numerous hand pits.
Avalanche Details
Avalanche Details: 
Date and Time of Avalanche: 
Saturday, February 17, 2018 - 20:00
Avalanche Type: 
Soft Slab
Failure Plane/Weak Layer: 
Other - explain below
More information or comments about the avalanche: 

An 18-24" storm slab that failed on the 2/8 rain crust. This avalanche was located on a convexity in a forested location.

Hide Trigger
Trigger: 
natural
Hide Terrain
Start Zone Slope Angle: 
35
Aspect: 
North
Starting Elevation: 
near-treeline
Hide Size
Destructive Size: 
D1 Relatively harmless to people.
Relative Size: 
R1 Very Small
Crown Height: 
2 ft
Avalanche Length (Vertical Run): 
25ft.
Avalanche Width (Average width): 
30ft.
Avalanche Location: