Widespread Persistent Weak Layers at the surface

Location Name: 
Forecaster Observation - Mt. Thompson-Seton, Whitefish Range
Observation date: 
Saturday, December 9, 2017 - 12:30
Is this an Avalanche Observation: 
Yes
Observation made by: Forecaster

Tabs

Quick Observation

In wind sheltered terrain, last week's storm snow, up to 10" deep, is quickly losing cohesion due to faceting.  In this type of terrain, there were no slab avalanche concerns but some minor sluffing running on the Thanksgiving rain crust.  There were small pockets of wind slab near ridgelines that didn't produce any signs of instability with a little prodding.  The big news is rampant surface hoar and near surface facet growth; all but the most wind battered slopes will have a troublesome weak layer/crust combo going into our next storm....whenever that is. 

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

December 9, 2017. Widespread persistent weak layers in the Norther Whitefish Range

Travel Details
Region: 
Whitefish Range - Northern (north of Coal Creek)
Route Description: 

Up Ninko Creek to the summit of Mt. Thompson-Seton

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
Persistent Weak Layers: 
On the surface
New Snow in the past 24 hours: 
0.00in.
More comments about the snowpack and weather: 
Above 6,500 feet, we observed surface hoar on all wind protected slopes. On steep, easterly slopes, surface hoar was forming over a soft and thin melt-freeze crust from solar input. At all elevations, the snow above the Thanksgiving crust is faceting (fist hard, ~1mm facets). This layer increases in thickness with elevation, up to 10" thick at 7,000 ft. Above 7,200 ft, the slopes we traveled on were wind affected, and surfaces varied from wind board to sastrugi to scoured back to the Thanksgiving crust. There were isolated drifts just below ridgelines from a NW loading pattern. We stomped at a few of them with no sign of instability.
Avalanche Details
Avalanche Details: 
Date and Time of Avalanche: 
Saturday, December 9, 2017 - 13:30
Avalanche Type: 
Loose Dry/ Sluff
Failure Plane/Weak Layer: 
New/old snow interface
More information or comments about the avalanche: 

Skier triggered one harmless facet sluff entraining the top 8" of faceted snow above the Thanksgiving crust.

Hide Trigger
Trigger: 
skier
Trigger Modifier: 
Intentionally Triggered
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Start Zone Slope Angle: 
38
Aspect: 
Northeast
Starting Elevation: 
above-treeline
Hide Size
Destructive Size: 
D1 Relatively harmless to people.
Relative Size: 
R1 Very Small
Avalanche Length (Vertical Run): 
300ft.
Avalanche Location: