Storm slabs in Marion

Location Name: Forecaster Observation - Marion Lake, Flathead Range Observation date: Wednesday, February 13, 2019 - 15:30	Is this an Avalanche Observation: Yes

Observation made by: Forecaster

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Quick Observation

We traveled to the Flathead Range to assess the after effects of recent heavy snow.

Settled snow totals since Sunday range from 24" at 4300' to 30"+ at 5800'
A storm slab avalanche cycle occurred late Tuesday evening/early Wednesday morning. 10-15 crowns were spotted in the Marion drainage with several of these crowns exceeding one foot in height. Our tour was limited by the deep snow and we are convinced there were other crowns not visible from our location.
A Loose Dry avalanche cycle also occurred during the same Tuesday evening/Wednesday morning time frame.
Instabilities noted today include collapsing and frequent cracking. The cracking was interesting in that the cracks would consistently penetrate the recent storm snow to a depth of 18-24".

Snowpack, Avalanche, Weather Images:

Travel Details

Region:

Flathead Range - Middle Fork Corridor

Activity:

Skiing

Snowpack Details

Snowpack and Weather Details:

Terrain

Elevation of observation:

3500-5000 ft

5000-6500 ft

Aspect(s) of observation:

Red Flags:

Collapsing / whumpfing noises

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

Blowing snow

Persistent Weak Layers:

Not observed

More comments about the snowpack and weather:

The storm snow remained dry and low-density despite the warming temperatures. SW winds kicked up in the afternoon drifting snow and knocking tree bombs off of large spruce trees. The amount of new snow in the past 24 hours was difficult to discern. It is easier to just look at the settled snow depth since Saturdays Arctic intrusion.

Blowing Snow:

Light

Wind Speed:

Moderate (Small trees sway)

Wind Direction:

Southwest

Air temperature:

Below Freezing

Snow line:

2000

Sky Cover:

Decreasing Clouds

Highest Precipitation Rate:

Moderate Snowfall (S2)

Avalanche Details

Avalanche Details:

Date and Time of Avalanche:

Wednesday, February 13, 2019 - 00:30

Avalanche Type:

Soft Slab

Failure Plane/Weak Layer:

Within storm snow

More information or comments about the avalanche:

The slides ranged in size from R1D1 to R2D2. Crown heights were 6"-18". These occurred on the south and north aspects. We are sure that there were slides which we could not see from our vantage point on the valley floor. We could not discern any slides on the 7800' peak at the head of the lake but we were looking at this peak from a long ways away (foot of Marion Lake).

Trigger

Trigger:

natural

Terrain

Start Zone Slope Angle:

Starting Elevation:

5000-7000'

Avalanche Location:

Date and Time of Avalanche:

Wednesday, February 13, 2019 - 00:30

Avalanche Type:

Loose Dry/ Sluff

Failure Plane/Weak Layer:

Within storm snow

More information or comments about the avalanche:

These were found on north and south aspects.

Trigger

Trigger:

natural

Terrain

Start Zone Slope Angle:

Starting Elevation:

5000-7000'

Size

Destructive Size:

D1 Relatively harmless to people.

Relative Size:

R1 Very Small

Avalanche Location:

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