Storm snow cycle in the Middle Fork

Location Name: Forecaster Observation - Wahoo, Rescue Creeks, Flathead Range Observation date: Thursday, February 15, 2018 - 18:00	Is this an Avalanche Observation: Yes

Observation made by: Forecaster

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Quick Observation

~12" of relatively low-density storm snow over the VDay facet & 2/8 rain crust. Minimal wind effect where we traveled, but we saw blowing snow on higher peaks.
Widespread storm slab and loose snow avalanche cycle occurred last night, all elevations, D1 to D2 in size. Slides ran on the rain crust about a foot deep.
Most crowns were not in "typical" start zones. They failed lower on slopes in wind sheltered terrain, where the VDay facet layer was preserved from Sunday's wind beating. Considering how soft and shallow the slabs were, they showed impressively wide propagation.
We had good visibility of the alpine and did not see any slides that stepped down to deeper layers.
We observed some minor cracking and collapsing, but surprisingly, we weren't able to produce any slab avalanche results on suspect slopes with ski cuts. It was easy to trigger loose snow avalanches.
Current snow surface is low-density stellar dendrites...another potential weak layer for this weekend's storm.

Snowpack, Avalanche, Weather Images:

Snowpack, Avalanche, Weather Videos:

February 15, 2018. Storm slab cycle in the Flathead Range

Travel Details

Region:

Flathead Range - Middle Fork Corridor

Route Description:

Rescue Creek and Wahoo Creek up to 6,000'

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)

Persistent Weak Layers:

Buried

New Snow in the past 24 hours:

12.00in.

More comments about the snowpack and weather:

Fist hard slab (8 to 14") over fist hard weak layer (1mm facets), over the well documented 2/8 rain crust. Southerly aspects developed a thin sun crust today. From 4500-5000', we found a crust/facet/crust sandwich below the new snow. The upper crust was thin, soft and collapsing under foot.

Avalanche Details

Avalanche Details:

Date and Time of Avalanche:

Wednesday, February 14, 2018 - 23:00

Avalanche Type:

Soft Slab

Failure Plane/Weak Layer:

New/old snow interface

More information or comments about the avalanche:

More than 25 storm slabs on all aspects & elevations. Ranged from D1 to D2. Most commonly failed in wind-sheltered terrain below 6,000', although there were a few D2s from higher terrain as well.

Trigger

Trigger:

natural

Size

Destructive Size:

D1.5

Relative Size:

R2 Small

Crown Height:

1 ft

Avalanche Location:

Date and Time of Avalanche:

Wednesday, February 14, 2018 - 23:30

Avalanche Type:

Loose Dry/ Sluff

Failure Plane/Weak Layer:

New/old snow interface

More information or comments about the avalanche:

More than 50 D1 to D2 loose snow avalanches, all elevations and aspects.

Trigger

Trigger:

natural

Size

Destructive Size:

D1.5

Relative Size:

R1 Very Small

Crown Height:

1 ft

Avalanche Location:

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Storm snow cycle in the Middle Fork

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February 15, 2018. Storm slab cycle in the Flathead Range

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February 15, 2018. Storm slab cycle in the Flathead Range

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