Wind Tunnel Ridge

Location Name: Forecaster Observation - Tunnel Ridge Observation date: Saturday, December 29, 2018 - 15:45	Is this an Avalanche Observation: Yes

Observation made by: Forecaster

Location

Tabs

Quick Observation

Strong winds rapidly created a reactive Wind Slab avalanche problem along/ near ridges above 6,000 feet.

Triggered multiple small wind slabs (E and NW aspects); found one fresh natural avalanche on a cross-loaded slope (SE).
Shooting cracks in fresh drifts up to 100 feet long and a foot or so deep. Some remotely triggered.
Two quick snow profiles to assess Persistent Slab avalanche problem showed strenghtening and unreactive weak layers (12/9 and Thanksgiving).
We avoided steep, windloaded terrain features and found stable skiing in windsheltered terrain.

Snowpack, Avalanche, Weather Images:

Snowpack, Avalanche, Weather Videos:

December 29, 2018. Wind slab instabilities in the Flathead

Travel Details

Region:

Flathead Range - Middle Fork Corridor

Route Description:

Up Tunnel Ridge to 7,000'

Activity:

Skiing

Snowmobiling

Snowpack Details

Snowpack and Weather Details:

Terrain

Elevation of observation:

5000-6500 ft

Above 6500 ft

Aspect(s) of observation:

Red Flags:

Shooting cracks

Blowing snow

Persistent Weak Layers:

Facets or Faceted Crust

Buried

New Snow in the past 24 hours:

4.00in.

Total Snow Depth:

More comments about the snowpack and weather:

Overcast or broken skies, snow showers, and a weeee bit o'wind. WInd speeds jumped about midday, with strong winds reaching down below ridges. At ridges, intense wind loading rapidly built sensitive cornices and small slabs. Triggered several of these remotely. Most fresh slabs thinned a short distance down slope and didn't run much past their stauchwalls. One exception was a cross-loaded pocket on the windward (N-NW aspect) side of the ridge. Steeper slope, possibly weaker snow at old snow surface.

Blowing Snow:

Intense

Wind Speed:

Strong (Whole trees in motion)

Wind Direction:

West

Air temperature:

Below Freezing

Snow line:

3250'

Sky Cover:

Mostly Cloudy (BRK)

Highest Precipitation Rate:

Light Snowfall (S1)

Avalanche Details

Avalanche Details:

Date and Time of Avalanche:

Saturday, December 29, 2018 - 13:30

Avalanche Type:

Soft Slab

Failure Plane/Weak Layer:

New/old snow interface

More information or comments about the avalanche:

Small slabs and cornices that failed with body weight on ridge. Most did not run past their stauchwalls. Brodering on hard slab.

Trigger

Trigger:

skier

Trigger Modifier:

Intentionally Triggered

Terrain

Start Zone Slope Angle:

Aspect:

East

Starting Elevation:

above-treeline

Size

Destructive Size:

D1 Relatively harmless to people.

Relative Size:

R1 Very Small

Crown Height:

1 ft

Avalanche Length (Vertical Run):

25ft.

Avalanche Width (Average width):

25ft.

Avalanche Location:

Date and Time of Avalanche:

Saturday, December 29, 2018 - 13:30

Avalanche Type:

Soft Slab

Failure Plane/Weak Layer:

New/old snow interface

More information or comments about the avalanche:

Dense drift on ridgeline. Fractured downslope; couldn't see how far it ran.

Trigger

Trigger:

skier

Trigger Modifier:

Intentionally Triggered

Terrain

Start Zone Slope Angle:

Aspect:

Northwest

Starting Elevation:

above-treeline

Size

Destructive Size:

D1.5

Relative Size:

R1 Very Small

Crown Height:

1 ft

Avalanche Width (Average width):

100ft.

Avalanche Location:

Date and Time of Avalanche:

Saturday, December 29, 2018 - 13:00

Avalanche Type:

Soft Slab

Failure Plane/Weak Layer:

New/old snow interface

More information or comments about the avalanche:

On southeast side of Pt. 6703. Could not see how far it ran, so couldn't estimate a size. Guessing D1.5.

Trigger

Trigger:

natural

Terrain

Start Zone Slope Angle:

Aspect:

Southeast

Starting Elevation:

above-treeline

Size

Destructive Size:

unknown

Relative Size:

unknown

Crown Height:

1 ft

Avalanche Width (Average width):

30ft.

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December 29, 2018. Wind slab instabilities in the Flathead

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December 29, 2018. Wind slab instabilities in the Flathead

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