Snowcat triggered avalanche

Location Name: 
Forecaster Observation - Werner Peak Road, S. Whitefish Range
Observation date: 
Wednesday, February 7, 2018 - 12:45

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

Location

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Quick Observation

Flathead Avalanche Center staff visited to the location of a partially buried snowcat on the Werner Peak road, south of Werner Peak proper. On Tuesday night (February 6th) at approx. 2345, a snowcat was grooming the Werner Peak road when they accidently triggered a 35 degree slope above the road. The avalanche failed approx. 3 feet deep, propagated approx. 150 feet wide, and ran approx. 50 feet downhill stopping on the road grade below. The avalanche failed on what is believed the 12/17 rain crust with 0.5 mm facets above the crust. It does not appear the avalanche failed naturally. The avalanche deposited 8 to 10 feet of debris onto the road, burying the uphill side of the snowcat, but leaving the downhill side of the snowcat visible. The snowcat operator was not injured in the incident and was evacuated approx. 1 to 2 hours afterwards by a third party (exact time unknown). Flathead Avalanche Center was informed of the incident on Wednesday morning, February 7th. Currently, the Werner Peak road is impassible at the avalanche location but not closed.

Snowpack, Avalanche, Weather Images: 
Snowpack, Avalanche, Weather Videos: 

February 7, 2018 - Snowcat Triggered Avalanche

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

Accessed Canyon Creek road trailhead via North Fork road. Traveled Canyon Creek road through the notch, then followed the series of groomed trails to the location of the buried snowcat on the Werner Peak road, just south of Werner Peak proper.

Activity: 
Skiing
Snowmobiling
Snowpack Details
Snowpack and Weather Details: 
Hide Terrain
Elevation of observation: 
Above 6500 ft
Aspect(s) of observation: 
SW
Red Flags: 
Blowing snow
Persistent Weak Layers: 
Buried
New Snow in the past 24 hours: 
0.50in.
Total Snow Depth: 
128 cm
More comments about the snowpack and weather: 
Snowpack consist of multiple rain crust formed from multiple rain on snow events followed by cooler temperatures throughout the season. We observed a storm slab in the upper snowpack that formed during last week's storm/ loading event. The layer of concern is located 49 cm above the ground (0 cm is located at the ground below the entire snowpack) where small grain facets (0.5 mm) are sitting above a pencil hard rain crust. The crust/ weak layer combo provided a planar, slippery sliding surface for the slab to fail and slide down-slope. At the ground, advanced depth hoar (3-5 mm) was observed below an ice hard rain crust that formed at Thanksgiving. Stability test produced two propagating results, one in the storm slab (ECTP 14 at 90 cm) and the second on the same failure plane of the avalanche (ECTP 19 at 49 cm). The top 38 cm of storm slab produced non-propagating results during our snowpack assessment. We didn't observe any other signs of instability such as cracking or collapsing below our skis and snowmobiles or recent avalanche activity.
Avalanche Details
Avalanche Details: 
Date and Time of Avalanche: 
Tuesday, February 6, 2018 - 23:45
Avalanche Type: 
Hard Slab
Failure Plane/Weak Layer: 
Old snow
Hide Trigger
Trigger: 
Snowcat
Trigger Modifier: 
Accidentally Triggered
Hide Terrain
Start Zone Slope Angle: 
35
Aspect: 
Southwest
Starting Elevation: 
above-treeline
Hide Size
Destructive Size: 
D2 Could bury, injure, or kill a person.
Relative Size: 
R3 Medium
Crown Height: 
3 ft
Avalanche Length (Vertical Run): 
50ft.
Avalanche Width (Average width): 
150ft.
Hide People Involved
Number of people caught: 
1
Number of partial burials: 
1
Number of full burials: 
0
Avalanche Location: