Swarm of storm slabs

Location Name: Forecaster Observation - WMR Sidecountry Observation date: Tuesday, February 12, 2019 - 21:15	Is this an Avalanche Observation: Yes

Observation made by: Forecaster

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Quick Observation

Backcountry slopes accessed from Whitefish Mountain Resort, to monitor conditions as storm progressed

WIdespread natural avalanche cycle late Monday night/ early Tuesday morning. wall-to-wall cracking or natural avalanches on 90% of the slopes 35* or steeper on east, northeast, north, and northwest sides of Ghoulie Point.
Natural avalanches were 2-8" deep; soft slabs (Fist+ hardness) running on very low density snow (Fist) from Monday. Slopes less than about 35* cracked/ shattered but blocks did not slide more than a few inches.
Cracking was limited to 5-10 feet while traveling, and seemed to be shorter and less common as day progressed.
Heard/ felt no whumpfing or collapses
1-2" of faceted snow above the Groundhog Crust did not propagate in column tests; saw no triggered slides that stepped down to this layer.
Stuck to slopes 30* or less, or those less than 35* that had already slid.

Snowpack, Avalanche, Weather Images:

Snowpack, Avalanche, Weather Videos:

20190212 Natural Avalanche Cycle, southern Whitefish Range

Travel Details

Region:

Whitefish Range - Southern (south of Coal Creek)

Route Description:

WMR Sidecountry - Ghoulies Point area

Activity:

Skiing

Snowpack Details

Snowpack and Weather Details:

Terrain

Elevation of observation:

5000-6500 ft

Aspect(s) of observation:

Red Flags:

Shooting cracks

Persistent Weak Layers:

Facets or Faceted Crust

Buried

New Snow in the past 24 hours:

5.00in.

More comments about the snowpack and weather:

Snow showers most of the day, lightest early afternoon. Otherwise S1 w bursts of S2. Light-moderate southerly winds. Some fresh chalky drifts near ridges; no slab development. Test profile at 6400 ft, NE, 30* CT3 RP/ ECTN2 12 cm down below Monday night's snow. 2/2 Groundhog crust ~1 cm thick , p hard, not deteriorating as I've seen elsewhere. More a rain crust/ pane of glass. ~5 cm F hard FC above this potential bed surface. ECTN H CT M BRk in tests.

Blowing Snow:

Light

Wind Speed:

Light (Twigs in motion)

Wind Direction:

South

Snow line:

4000

Sky Cover:

Obscured by fog, etc (X)

Highest Precipitation Rate:

Moderate Snowfall (S2)

Avalanche Details

Avalanche Details:

Date and Time of Avalanche:

Tuesday, February 12, 2019 - 21:15

Avalanche Type:

Soft Slab

Failure Plane/Weak Layer:

New/old snow interface

More information or comments about the avalanche:

From depth and new snow on bed/ shattered slabs, estimate that slides ran early this morning, during peak precip intensity

Trigger

Trigger:

natural

Terrain

Start Zone Slope Angle:

Aspect:

East

Starting Elevation:

above-treeline

Size

Destructive Size:

D1.5

Relative Size:

R2 Small

Crown Height:

Less than 1 ft

Avalanche Length (Vertical Run):

100ft.

Avalanche Width (Average width):

75ft.

Avalanche Location:

Date and Time of Avalanche:

Tuesday, February 12, 2019 - 21:45

Avalanche Type:

Soft Slab

Failure Plane/Weak Layer:

New/old snow interface

More information or comments about the avalanche:

Nearly continuous line of crowns across NE-facing slopes below Ghoulie Point, w slides actually running on slopes ~35* and steeper and just shattering on slightly lower slope angles. F hard slab of new snow over F- low density snow from Monday

Trigger

Trigger:

natural

Terrain

Start Zone Slope Angle:

Aspect:

Northeast

Starting Elevation:

6400

Size

Destructive Size:

D1.5

Relative Size:

R2 Small

Crown Height:

Less than 1 ft

Avalanche Length (Vertical Run):

100ft.

Avalanche Width (Average width):

75ft.

Avalanche Location:

Date and Time of Avalanche:

Tuesday, February 12, 2019 - 21:45

Avalanche Type:

Soft Slab

Failure Plane/Weak Layer:

New/old snow interface

More information or comments about the avalanche:

Shattered slabs and small natural avalanches on mid slope openings on densely forested slope. Not the kind of slopes that pop out as start zones.

Trigger

Trigger:

natural

Terrain

Start Zone Slope Angle:

Aspect:

Northwest

Starting Elevation:

6300

Size

Destructive Size:

D1 Relatively harmless to people.

Relative Size:

R2 Small

Crown Height:

Less than 1 ft

Avalanche Length (Vertical Run):

75ft.

Avalanche Width (Average width):

50ft.

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20190212 Natural Avalanche Cycle, southern Whitefish Range

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