Pro Field Report

Basic Information

Observation Details

Observation Date:
December 8, 2019
Submitted:
December 8, 2019
Observer:
SAC - Lundy, Haskins (Rec)
Zone or Region:
Banner Summit
Location:
Copper

Signs of Unstable Snow

Recent Avalanches? 
Yes
Cracking? 
Widespread
Collapsing? 
Widespread
Widespread cracking and collapsing on upper elevation shady aspects with old, pre-Thanksgiving snow. Collapses/cracks seemed about 40cm deep into faceted basal snow.

Snow Stability

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

Bottom Line

12 inches of dense new snow was enough to produce obviously unstable conditions on slopes with a pre-Thanksgiving snowpack. Several weak layers exist, including recently formed surface hoar beneath the new snow as well as deeper facets from the October snow.

Media/Attachments

Mid storm cracking with a small natural avalanche.
On Banner Summit, Chris experienced widespread shooting cracks on upper elevation, shady slopes. Natural and triggered avalanches occurred on nearby slopes. 8700', NE.
Widespread cracking on upper elevation, shady slopes.

Advanced Information

Weather Summary

Cloud Cover:
Overcast
Temperature:
~ mid to upper 20s F
Wind:
Light , NW

30cm new snow at all elevations.

Avalanche Observations

 #  Date Location Size Type Bed Sfc Depth Trigger Comments Photo
1 Down the ridge from Copper summit
NE 8600 		D1 SS O-Old Snow 30-40cm AS-Skier
r-Remote 		Triggered remotely with a cornice drop. None
2 Down the ridge from Copper summit
NE 8600 		D1.5 SS O-Old Snow 30-40cm N-Natural Two natural avalanches observed. One was D1 and occurred midstorm. The other (in the photo) was D1.5 and a bit more fresh looking.

Snowpack Observations

Average snow depth ranged from around 40cm at the highway to around 80cm on upper elevation shaded aspects. At lower elevations and on solars, the new snow fell onto bare ground or just a bit of snow. Relatively widespread 1-3cm SH beneath the new snow at the 12/7 interface - see photo of a SW aspect at 8400'. Upper elevation shaded aspects have a weak MF crust beneath the Thanksgiving snow with depth hoar below. Collapsing and cracking was widespread in these areas - walking in undisturbed snow would spider web the vicinity with cracks. We remotely triggered one small slide with a cornice drop.

Surface hoar buried by the 12/7 storm.

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: 30-40cm/20191127 & 20191207
Comments: The 20191207 SH is a bit more widespread but less reactive due to having less slab.

Terrain Use

We planned to avoid avalanche terrain, and the widespread signs of instability gave us no reason to change that plan!