Oh No No near Great Northern

Location Name: Forecaster Observation - Crystal Cr, Flathead Range Observation date: Monday, January 15, 2018 - 18:00	Is this an Avalanche Observation: Yes

Observation made by: Forecaster

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Quick Observation

Got views of more slab avalanche activity, most of which ran last storm, from D2 to D4. The largest was a hard slab on Great Northern that I would guess is 8' to 15'+ (?) deep, that sounds like it ran Monday evening. I noticed it Tuesday morning.
Surface hoar is fairly widespread where we traveled, over faceting snow on shady slopes or on top of melt-freeze crusts on sunny slopes and lower elevations.
No collapses or cracking while breaking trail. Last week's storm snow felt less cohesive, due to faceting, than last time I traveled in this region on Saturday. However, stability tests produced moderate, propagating results on a small-grained facet layer below the recent rain crust, 55 cm deep at 5800'. About 400' higher, the crust was seemingly welded to underlying rounds. Go figure.

Snowpack, Avalanche, Weather Images:

Travel Details

Region:

Flathead Range - Middle Fork Corridor

Route Description:

Up the ridge that divides Crystal and Stanton to 6,350. Descended through Crystal Creek

Snowpack Details

Snowpack and Weather Details:

Terrain

Elevation of observation:

3500-5000 ft

5000-6500 ft

Above 6500 ft

Aspect(s) of observation:

Persistent Weak Layers:

On the surface

Buried

New Snow in the past 24 hours:

0.00in.

Total Snow Depth:

240 cm

More comments about the snowpack and weather:

ECTP 19, SC down 55 cm on small facets below 1/9 rain crust at 5800'. At 6200', No result in CT on the same layer, down 85 cm.

Avalanche Details

Avalanche Details:

Date and Time of Avalanche:

Saturday, January 13, 2018 - 05:00

Avalanche Type:

Hard Slab

Failure Plane/Weak Layer:

Ground

More information or comments about the avalanche:

Sub peak of Great Northern., viewed from a long distance away. Looks like a glide crack released and triggered a hard slab.

Trigger

Trigger:

natural

Terrain

Aspect:

North

Starting Elevation:

above-treeline

Size

Destructive Size:

D4 - Could destroy a rail car, large truck, buildings, or swaths of forest

Relative Size:

R4 Large

Crown Height:

More than 10 ft

Avalanche Width (Average width):

1900ft.

Avalanche Location:

Date and Time of Avalanche:

Saturday, January 13, 2018 - 05:30

Avalanche Type:

Soft Slab

Failure Plane/Weak Layer:

Unknown

More information or comments about the avalanche:

Various debris piles below Nyack. Couldn't really see the crowns; saw one that looked about 4 to 5 feet, and one that looked smaller <2ft.

Trigger

Trigger:

natural

Terrain

Aspect:

Northeast

Starting Elevation:

above-treeline

Size

Destructive Size:

D2.5

Relative Size:

unknown

Avalanche Location:

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