Pro Field Report

Basic Information

Observation Details

Observation Date:
December 22, 2020
Submitted:
December 23, 2020
Observer:
Chris Lundy (off duty)
Zone or Region:
Banner Summit
Location:
South of Copper (6900-8800', most aspects)

Signs of Unstable Snow

Recent Avalanches? 
Yes
Cracking? 
None Experienced
Collapsing? 
Isolated
Widespread avalanche activity on a variety of aspects and elevations. Most terrain over 35 degrees avalanches at upper elevations.

Snow Stability

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

Bottom Line

Avalanche conditions are dangerous. If there wasn't much of a slab before, there is now. A 16-24", relatively dense slab sits atop the very weak facet layer. Stability test scores remain poor, and the moderate to strong NW winds were continuing to load upper elevation slopes. Only felt two medium collapses.

Advanced Information

Weather Summary

Cloud Cover:
Obscured
Temperature:
teens F
Wind:
Moderate , NW

S-1 most of the day. 7-10cm of low density new snow by mid-afternoon. NW winds at ridge level were M gusting to S and transporting snow.

Avalanche Observations

 #  Date Location Size Type Bed Sfc Depth Trigger Photos Details
10 Dec 21, 2020
(+/- 1 day) 		Two bowls south of Copper Mtn, draining into Swamp Creek
NE 8800ft 		D2 SS-Soft Slab O-Old Snow 1.5ft N-Natural
Widespread avalanching in a bowl to the south of Copper Mountain in the Banner Summit zone. This terrain faces NE at 8800'. The crowns are 1.5-2 feet deep. The light is poor, but most of the terrain that was steep enough to slide, slid.
This avalanche released in a bowl south of Copper Mountain in the Banner Summit zone. It broke 18-20" deep and several hundred feet wide. E facing slope at 8600'.
Snowpit at 8800' on an E aspect near Copper Mountain in the Banner Summit zone. The test failed 2' deep (ECTP14) on the very weak facet layer. This pit was located above a slope that avalanched naturally.
Report
10 Dec 21, 2020
(+/- 1 day) 		Bowl south of Copper Mtn
NE 8700ft 		D2 SS-Soft Slab O-Old Snow 1.5ft N-Natural
Multiple avalanches that released on Copper Mountain in the Banner Summit Zone. These broke 1.5-2' deep on the facet layer that formed during the Nov/Dec dry spell. 8600-8700', E-NE.
Natural avalanche that broke 20-24" deep near Copper Mountain in the Banner Summit zone. 8800', NE.
Report
1 Dec 21, 2020
(+/- 1 day) 		Base of Copper Mtn
N 7100ft 		D1.5 SS-Soft Slab O-Old Snow 0.5ft N-Natural
A natural avalanche that occurred at lower elevations near the base of Copper Mountain in the Banner Summit zone. It broke 16" deep on the 12/11 facets. 7100', N.
Crown profile of a low elevation avalanche near the base of Copper Mountain in the Banner Summit zone. It broke 16" deep on the 12/11 facets. A stripe of surface hoar (12/13?) is visible but the avalanche seems to have broke in the 12/11 facets below it. 7100', N.
Report
1 Dec 21, 2020
(+/- 1 day) 		Base of Copper along HWY 21
NW 6979ft 		D1.5 SS-Soft Slab N-Natural
A natural avalanche visible from HWY 21 in the Banner Summit zone, near the start of the ascent to Copper Mountain. 7000', WNW.
Report
Two bowls south of Copper Mtn, draining into Swamp Creek
Bowl south of Copper Mtn
Base of Copper Mtn
Base of Copper along HWY 21

Widespread and extensive cycle of avalanches failing on the 12/11 facets breaking 40-60cm deep. Occurred at a variety of elevations. Pattern seemed to be primarily on shadier aspects, I did not see any on steep, low and mid elevation solars that were plenty steep. It's notable that a number of D2's ran in terrain that had weak basal snow, and none were observed to have stepped down. See avalanche observations for more details.

Snowpack Observations

Where to begin? It's a whole new world out there.

Crusts from rain exist to the mountain tops here (8900'). Thickness ranged from 4-5cm at the valley bottom to a soft 1-2cm up high. These are topped with 7-10cm of light snow. Crusts at low elevations are probably stout enough to increase snowpack stability. I didn't see where rain percolated deeper than 10cm or so.

Slab depth on 12/11 facet layer ranged from 40cm off the valley floor to 60cm at upper elevations. Slab hardness is generally 4F nearly throughout. Facet layer hardness was F (which is better than it was before loading: F-), and dry everywhere I looked.

@8000', WNW: HS 115cm. Slab 50cm thick, ECTP13 x2. Got medium collapse on this slope. See first photo below.

@8800', E: HS 140cm. Slab 60cm thick. ECTP14. This pit was 100' above the crown of a D2 avalanche.

8000', WNW: ECTP13 on 12/11 facets buried 50cm deep.
Snowpit at 8800' on an E aspect near Copper Mountain in the Banner Summit zone. The test failed 2' deep (ECTP14) on the very weak facet layer. This pit was located above a slope that avalanched naturally.

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: 40-60cm
Weak Layer(s): Dec 11, 2020 (FCsf)
Comments: Poor layering also exists at low elevations, but stout surface crusts are making it less reactive.

Wind was actively transporting snow, but I did not observe much in the way of sensitive wind slabs.

Terrain Use

I avoided avalanche terrain. Ski conditions were weird at best and dangerous at worst.