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Professional Observation

Basic Information

Observation Details

Observation Date:
December 15, 2019
Submitted:
December 16, 2019
Observer:
SAC - VandenBos
Zone or Region:
Galena Summit and Eastern Mtns
Location:
4th of July Creek Drainage

Signs of Unstable Snow

Recent Avalanches? 
Yes
Cracking? 
Widespread
Collapsing? 
Widespread
Collapsing a bit more touchy on the north half of the compass, but still reactive on the south half. Difficult to tell if collapses were on surface hoar or depth hoar (discussed below)

Snow Stability

Stability Rating: 
Poor
Confidence in Rating: 
High
Stability Trend: 
Steady

Bottom Line

A layer of surface hoar is buried at the 12/7 interface in the White Clouds. This layer is very similar in appearance and behavior to the surface hoar that I've been finding in the Smokys, Sawtooths, and Banner Summit areas. It is showing no signs that it will heal quickly. Underneath this layer is an ugly combination of depth hoar on a melt-freeze crust. This layer produced natural activity and unstable snowpack test results and is also showing no signs of healing quickly.

Advanced Information

Weather Summary

Cloud Cover:
Partly Cloudy
Temperature:
single digits to mid teens F (estimated)
Wind:
Moderate , NW

Moderate NW winds blowing along ridge lines, moving small amounts of snow.

Avalanche Observations

 #  Date Location Size Type Bed Sfc Depth Trigger Comments Photo
2 Today 4th of July Creek
NE 		O-Old Snow 40-50cm AS-Skier
r-Remote 		Remotely triggered 2 slides from above on safe ridge line, 1 D1 and 1 D2. Culprit weak layer appeared to be 12/7 SH, which was reactive in snowpack tests and hand shears. None
1 Past 48 hours 4th of July Creek
NE 9,400 		D2.5 SS O-Old Snow 50-80cm N-Natural Large slide running on DH/large grained FC on top of early season MFcr. 600-800' wide in main slide, some D2 pockets several hundred feet away likely ran sympathetically.
This large natural avalanche was observed in the 4th of July Creek drainage in the White Cloud Mountains. It failed at the tail end of last weeks storm on a layer of depth hoar near the ground. E-NE aspect, 9,400'.
1 Past 48 hours McDonald Peak
NE 9,400'
This large natural avalanche ran during the most recent storm. It failed on a NE aspect at 9,400' on McDonald Peak in the Sawtooth Mountains

Avalanche Problems

Problem Location Distribution Sensitivity Size Comments
Persistent Slab
Isolated
Specific
Widespread
Unreactive
Stubborn
Reactive
Touchy
D1
D1.5
D2
D2.5
D3
D3.5
D4
D4.5
D5
 Layer Depth/Date: 12/7 SH, down 40-45cm
Persistent Slab
Isolated
Specific
Widespread
Unreactive
Stubborn
Reactive
Touchy
D1
D1.5
D2
D2.5
D3
D3.5
D4
D4.5
D5
 Layer Depth/Date: 11/26 DH, down 55-60cm
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