If it slides like a slab, and comes from a storm...

Location Name: 
Forecaster Observation: Southern Whitefish Range
Observation date: 
Friday, December 20, 2019 - 18:45
Is this an Avalanche Observation: 
Yes
Observation made by: Forecaster

Location

Tabs

Quick Observation

We went sledding and skiing in the southern Whitefish Range to look at instabilities from the most recent storm. Found some too.

  • Despite a few "false stable" test pit results, we could trigger 10 inch thick storm slabs on steep, mid elevation slopes. We got shooting cracks, and collapsing in the storm snow on adjacent slopes that didn't slide. 
  • The new snow was very upside-down with dense heavy snow over softer, fluffier snow below.
  • Snowline overnight seems to have been around 5,000'. There still isn't enought snow below that elevation to really get moving as an avalanche. However, we did find a few inches of very wet new snow at lower elevations causing roller balls and itty bitty point releases.
  • We saw some occasional blowing snow at ridgetops, but it seemed to have stopped after about 1pm. Middle and lower elevations were calm all day.
  • We were surprised at how little precipitation we saw during the day. No new snow of note while we were out. Drizzling rain off and on at the trailhead.
  • We avoided big steep slopes at mid elevations and upper elevations where we expected bigger, wind drifted slabs.
Snowpack, Avalanche, Weather Images: 
Snowpack, Avalanche, Weather Videos: 

Storm Slabs in the Whitefish Range

Travel Details
Region: 
Whitefish Range - Southern (south of Coal Creek)
Route Description: 

To 5,800'

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
S
SW
Red Flags: 
Shooting cracks
Blowing snow
Persistent Weak Layers: 
Facets or Faceted Crust
Buried
New Snow in the past 24 hours: 
10.00in.
Total Snow Depth: 
45in
More comments about the snowpack and weather: 
@5750' SW aspect: ECTN x2 on slight density changes in the new snow, CTE and CTM SP in the same layers.
Blowing Snow: 
Light
Wind Speed: 
Light (Twigs in motion)
Wind Direction: 
South
Air temperature: 
Above Freezing
Snow line: 
5500
Sky Cover: 
Overcast (OVC)
Highest Precipitation Rate: 
Light Rain (RL)
Avalanche Details
Avalanche Details: 
Date and Time of Avalanche: 
Friday, December 20, 2019 - 13:30
Number of avalanches: 
1
Avalanche Type: 
Soft Slab
Failure Plane/Weak Layer: 
Within storm snow
More information or comments about the avalanche: 
Hide Trigger
Trigger: 
skier
Trigger Modifier: 
Intentionally Triggered
Hide Terrain
Start Zone Slope Angle: 
40
Aspect: 
Southwest
Starting Elevation: 
near-treeline
Hide Size
Destructive Size: 
D1 Relatively harmless to people.
Relative Size: 
R1 Very Small
Avalanche Length (Vertical Run): 
20ft.
Avalanche Width (Average width): 
40ft.
Avalanche Location: