Well that wasn't terrible

Location Name: 
Forecaster Observation - Central Swan Range
Observation date: 
Thursday, January 30, 2020 - 15:45

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

Tabs

Quick Observation

We went to the central Swan Range to see conditions before the change to stormy weather this weekend.

  • We found hard wind slabs below ridgelines that were unreactive to cornice drops, but did propagate in snowpack tests with hard force. We saw minor cracking at a few of our kick turns in wind affected snow, but no shooting cracks.
  • We saw several recent storm slab avalanches on steep, leeward, upper elevation slopes. They ranged from very small to a large slab that had propagated across several features. More info in the avalanche tab.
  • We found the most recent ice crust to be thick and very hard. It was under about a foot of settled snow on windward slopes, down almost 2 feet where winds had drifted snow above it, and it was near the surface at wind scoured ridges.
  • We found graupel and mixed snow grains around the January crusts, but no developed persistent weak layers. We tested the snow above the crusts in a sheltered area and did not get any notable results. We tried piling snow on top of our test column to see if additional loading would change the situation and did get propagation with moderate force at an interface between storm layers about 18 inches deep.
  • It didn't warm enough where we were for loose wet avalanche conditions to develop. The snow stayed dry down to lower elevations.
  • Without any obvious signs of instability we were comfortable stepping out into steeper terrain. We avoided very steep wind loaded, rocky chutes. Instead we opted to ski planar, well supported alpine slopes one at a time, and steep wind sheltered slopes in the trees.

Video here

Snowpack, Avalanche, Weather Images: 
Travel Details
Region: 
Swan Range - West Side (Flathead Valley access)
Route Description: 

To 7100'

Activity: 
Skiing
Snowmobiling
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
W
NW
New Snow in the past 24 hours: 
1.00in.
Total Snow Depth: 
>3m
More comments about the snowpack and weather: 
Clouds waxed and waned throughout the day. Snow surfaces primarily graupel and DFs with riming on windward slopes. @7000', E aspect: ECTP 27 down ~50cm in 4F interface between 1F wind slabs. @6400', NE aspect: ECTN 20 down ~40cm in a thin layer of preserved PP between 4F hard rounds.
Wind Speed: 
Light (Twigs in motion)
Wind Direction: 
West
Air temperature: 
Below Freezing
Snow line: 
4000'
Sky Cover: 
Mostly Cloudy (BRK)
Avalanche Details
Avalanche Details: 
Date and Time of Avalanche: 
Tuesday, January 28, 2020 - 10:00
Number of avalanches: 
1
Avalanche Type: 
Soft Slab
Failure Plane/Weak Layer: 
New/old snow interface
Hide Trigger
Trigger: 
natural
Hide Terrain
Start Zone Slope Angle: 
45
Aspect: 
Northeast
Starting Elevation: 
above-treeline
Hide Size
Destructive Size: 
D2.5
Relative Size: 
R3 Medium
Crown Height: 
1 ft
Avalanche Length (Vertical Run): 
300ft.
Avalanche Width (Average width): 
200ft.
Avalanche Location: 
Date and Time of Avalanche: 
Tuesday, January 28, 2020 - 10:00
Number of avalanches: 
1
Avalanche Type: 
Soft Slab
Failure Plane/Weak Layer: 
New/old snow interface
Hide Trigger
Trigger: 
natural
Hide Terrain
Start Zone Slope Angle: 
45
Aspect: 
Northeast
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): 
50ft.
Avalanche Location: 
Date and Time of Avalanche: 
Tuesday, January 28, 2020 - 10:00
Number of avalanches: 
1
Avalanche Type: 
Soft Slab
Failure Plane/Weak Layer: 
New/old snow interface
Hide Trigger
Trigger: 
unknown
Hide Terrain
Start Zone Slope Angle: 
40
Aspect: 
Northeast
Starting Elevation: 
near-treeline
Hide Size
Destructive Size: 
D1 Relatively harmless to people.
Relative Size: 
R2 Small
Crown Height: 
Less than 1 ft
Avalanche Length (Vertical Run): 
100ft.
Avalanche Width (Average width): 
20ft.
Avalanche Location: