Jewel Basin Observation

Location Name: Forecaster Observation - Noisy & Jewel Basins, Swan Range Observation date: Tuesday, January 2, 2018 - 13:00	Is this an Avalanche Observation: No

Observation made by: Forecaster

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Quick Observation

We observed widespread evidence of the natural storm slab avalanche cycle that occurred in the Swan Range from 12/28-29.
Overall, storm slabs appeared to be gaining strength but we experienced isolated surface cracking in wind loaded locations.
We located one large natural persistent slab avalanche with a crown height greater than 5 ft.
- This avalanche occurred on a treed, east aspect at the top of a convexity.
- Bed surface was the Thanksgiving crust with facets above and below.
We observed widespread surface hoar formation (5-10 mm) to wind-sheltered slopes on all aspects and elevations.

Snowpack, Avalanche, Weather Images:

Snowpack, Avalanche, Weather Videos:

January 2, 2018 - Expect the Unexpected

Travel Details

Region:

Swan Range - West Side (Flathead Valley access)

Route Description:

Snowmobiled up the Jewel Basin Road to Camp Misery. Followed the standard skin route to the ridgeline between Noisy and Jewel Basin’s. Descended through the notch back to Camp Misery and out the road to the truck.

Activity:

Skiing

Snowmobiling

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.

More comments about the snowpack and weather:

Dug on a NW at 6500’ and an E aspect at 7000’. Approx. 1-1.5m of snow above the Thanksgiving rain crust (1 cm thick). Both pits had hard and cohesive snow (1F) sitting below crust. No evidence of 12/17 freezing rain crust in either pit. ECTN and CTM with Q2 shears in both pits when assessing recent storm slab instabilities. 5-10 mm surface hoar on wind-sheltered slopes on all aspects and elevations.

Avalanche Details

Avalanche Details:

Avalanche Type:

Hard Slab

Failure Plane/Weak Layer:

Old snow

More information or comments about the avalanche:

Time of avalanche is unknown but estimated to occurr during the 12/28-29 avalanche cycle when an Avalanche Warning was issued for the Swan Range.

Trigger

Trigger:

natural

Terrain

Start Zone Slope Angle:

Aspect:

East

Starting Elevation:

above-treeline

Size

Destructive Size:

D2 Could bury, injure, or kill a person.

Relative Size:

R4 Large

Crown Height:

5 ft

Avalanche Length (Vertical Run):

150ft.

Avalanche Width (Average width):

200ft.

Avalanche Location:

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