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Professional Observation

Basic Information

Observation Details

Observation Date:
January 13, 2020
Submitted:
January 14, 2020
Observer:
SAC - VandenBos
Zone or Region:
Galena Summit and Eastern Mtns
Location:
4th of July Creek

Signs of Unstable Snow

Recent Avalanches? 
Yes
Cracking? 
Widespread
Collapsing? 
Widespread
Cracking and collapsing was widespread in lower elevations where fresh wind slabs rested on base of small grained facets. These collapses traveled for up to ~100'. At middle elevation, I experienced a few collapses and some cracking in wind loaded areas with fresh drifts.

Snow Stability

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

Bottom Line

Weak layers in snowpack are being pushed towards their breaking points. In areas with the right terrain characteristics, large triggers are capable of producing large avalanches involving the entire season's snowpack.

Media

This large natural avalanche failed on a NE facing slope at 8600 in the 4th of July Creek Drainage in the White Cloud Mountains. It failed on weak snow near the ground and was triggered by a collapsing cornice.
This large natural avalanche failed on a NE facing slope at 8600 in the 4th of July Creek Drainage in the White Cloud Mountains. It failed on weak snow near the ground and was triggered by a collapsing cornice.

Advanced Information

Weather Summary

Cloud Cover:
Overcast
Wind:
Moderate , W

Afternoon weather obs. Broken to overcast skies, occasional periods of S-1 precip with no significant precipitation. Light to moderate westerly winds blowing at highway level and along ridges in exposed middle elevation terrain - calm otherwise.

Avalanche Observations

 #  Date Location Size Type Bed Sfc Depth Trigger Comments Photo
1 Past 24 hours 4th of July Creek drainage
NE 8,600 		D2 HS O-Old Snow 50-90cm N-Natural Failed on facets 10-15cm off ground. Hard to be certain if there was snow on this slope prior to Thanksgiving storms, but I think there probably was. However, facets/DH at and below failure interface were fairly small (to 4mm), which seems on the small side for 11/26. No SH found at this interface. If I had to bet I'd say 11/26 was the culprit.
This large natural avalanche failed on a NE facing slope at 8600 in the 4th of July Creek Drainage in the White Cloud Mountains. It failed on weak snow near the ground and was triggered by a collapsing cornice.

Snowpack Observations

Snowpack seems to be close to its breaking point where thin. Slide observed was triggered by a sizable cornice collapse, pointing to the need for a large trigger in current snowpack conformation.

Avalanche Problems

Problem Location Distribution Sensitivity Size Comments
Wind Slab
Wind slabs existed in an isolated to widespread distribution in most of the terrain that I traveled through.
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 and 12/7
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