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

Tabs

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: 
Hide Terrain
Elevation of observation: 
3500-5000 ft
5000-6500 ft
Above 6500 ft
Aspect(s) of observation: 
N
NE
E
W
NW
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.

Hide Trigger
Trigger: 
natural
Hide Terrain
Start Zone Slope Angle: 
37
Aspect: 
East
Starting Elevation: 
above-treeline
Hide 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: