Avalanches in Canyon Creek

Location Name: Forecaster Observation - Ghoulie Ridge, Whitefish Range Observation date: Tuesday, December 19, 2017 - 14:00	Is this an Avalanche Observation: Yes

Observation made by: Forecaster

Location

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Quick Observation

Very touchy and widespread mid-storm layer instability about 5" deep and harmless in size. Almosty everything steep enough slid naturally on this precip layer.
15" of storm snow over Sunday's freezing rain crust/facet layer was reactive in some areas, producing collapses, shooting cracks, and a few naturals D1 to D2 in size just below the crust on the facet layer. No signs of instability above the crust, although WMR patrol reported explosive-triggered avalanches failing on this layer. Several slides crossed Canyon Creek Road; the crowns in Skook Chutes looked to be about 12-18" deep.
I think the smaller storm totals here paired with the 12/17 freezing rain crust reduced the distribution of instabilities at this location today compared to what we saw in the Flathead Range yesterday. The crust is acting like an untrustworthy bridge over the facets; it requires additional loading or human triggering to get it to collapse on the facets. This will be a challenging problem to manage in the future, especially as slab sizes increase.

Snowpack, Avalanche, Weather Images:

Travel Details

Region:

Whitefish Range - Southern (south of Coal Creek)

Activity:

Skiing

Snowpack Details

Snowpack and Weather Details:

Terrain

Elevation of observation:

5000-6500 ft

Aspect(s) of observation:

Red Flags:

Shooting cracks

Collapsing / whumpfing noises

More than a foot of new snow or heavy snowfall rates (>1"/hr)

Persistent Weak Layers:

Buried

Total Snow Depth:

110 cm

More comments about the snowpack and weather:

Propagating test results on the 12/15 facet layer. Cracking and collapsing was easier to initiate near trees where the 12/17 crust layer thinned out.

Avalanche Details

Avalanche Details:

Date and Time of Avalanche:

Tuesday, December 19, 2017 - 13:00

Avalanche Type:

Soft Slab

Failure Plane/Weak Layer:

Unknown

More information or comments about the avalanche:

Could make out 3 seperate D1.5 - D2 slab avalanches that ran in Skook Chutes today

Trigger

Trigger:

natural

Terrain

Aspect:

South

Starting Elevation:

near-treeline

Size

Destructive Size:

D2 Could bury, injure, or kill a person.

Relative Size:

R2 Small

Crown Height:

1 ft

Avalanche Location:

Date and Time of Avalanche:

Tuesday, December 19, 2017 - 08:15

Avalanche Type:

Soft Slab

Failure Plane/Weak Layer:

Old snow

More information or comments about the avalanche:

Checked out one crown that ran on the 12/15 facet layer, about a foot deep.

Trigger

Trigger:

natural

Terrain

Aspect:

Northeast

Starting Elevation:

near-treeline

Size

Destructive Size:

D1.5

Relative Size:

R1 Very Small

Avalanche Length (Vertical Run):

350ft.

Avalanche Width (Average width):

100ft.

Avalanche Location:

Date and Time of Avalanche:

Tuesday, December 19, 2017 - 13:30

Avalanche Type:

Soft Slab

Failure Plane/Weak Layer:

Within storm snow

More information or comments about the avalanche:

At least 25 crowns observed on the same mid-storm precip layer, only 5" deep. All aspects

Trigger

Trigger:

natural

Terrain

Starting Elevation:

near-treeline

Size

Destructive Size:

D1 Relatively harmless to people.

Relative Size:

R1 Very Small

Crown Height:

Less than 1 ft

Avalanche Length (Vertical Run):

60ft.

Avalanche Width (Average width):

30ft.

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