Swan Range

Location Name: 
Forecaster Observation - Swan Range
Observation date: 
Sunday, February 21, 2021 - 16:45
Is this an Avalanche Observation: 
Yes
Observation made by: Forecaster

Tabs

Quick Observation

Today we went into the Swan Range to get a feel for wind slab distribution and sensitivity. We also spent a little extra time on a west-facing aspect looking at weak snow around the 1/13 crust.

  • Moderate to intense blowing snow above 6000'. 
  • West aspects had a wind stiffened slab that was roughly 8 to 10 inches thick.
  • Ski penetration on a west aspect near ridgeline was 12 inches. This tells us that there is still more snow available to transport into slabs on leeward aspects. 
  • There were a few natural cornice failures that occurred within the past day. They appeared to have only produced small slabs. 
  • No collapsing and only minor cracking around skis in wind drifted snow.
  • Extended column tests and deep tap tests yielded no results on buried weak layers near the 1/13 crust. More info in snowpack tab. 

Despite the lack of feedback today, recent avalanches from yesterday were a clear sign for us to stick to terrain with slope angles less than 30 degrees. 

Snowpack, Avalanche, Weather Images: 
Travel Details
Region: 
Swan Range - West Side (Flathead Valley access)
Activity: 
Skiing
Snowmobiling
Snowpack Details
Snowpack and Weather Details: 
Hide Terrain
Elevation of observation: 
3500-5000 ft
5000-6500 ft
Aspect(s) of observation: 
N
NE
W
NW
Red Flags: 
Avalanches from the past 2 days
Blowing snow
Persistent Weak Layers: 
Facets or Faceted Crust
Total Snow Depth: 
240
More comments about the snowpack and weather: 
See photo for pit. (coming soon). Faceted snow near the 1/13 crust on a west aspect was showing a low probability, high consequence scenario. There was a 1 to 2 cm layer of 2 to 3mm facets sandwiched between two crusts. The bottom crust is the 1/13 crust. The top crust was a thing, breakable crust. This is similar to what I observed on a south aspect in the Whitefish Range. No surface hoar was found.
Blowing Snow: 
Intense
Wind Speed: 
Moderate (Small trees sway)
Wind Direction: 
Southwest
Air temperature: 
Below Freezing
Sky Cover: 
Overcast (OVC)
Highest Precipitation Rate: 
Very Light Snowfall (S-1)
Avalanche Details
Avalanche Details: 
Date and Time of Avalanche: 
Sunday, February 21, 2021 - 08:00
Number of avalanches: 
2
Avalanche Type: 
Soft Slab
Failure Plane/Weak Layer: 
Within storm snow
Hide Trigger
Trigger: 
natural
Trigger Modifier: 
Cornice Fall Triggered
Hide Terrain
Start Zone Slope Angle: 
40
Aspect: 
Northeast
Starting Elevation: 
near-treeline
Hide Size
Destructive Size: 
D1 Relatively harmless to people.
Relative Size: 
R1 Very Small
Crown Height: 
Less than 1 ft
Avalanche Location: