Pro Field Report

Basic Information

Observation Details

Observation Date:
December 8, 2022
Submitted:
December 9, 2022
Observer:
SAC - VandenBos
Zone or Region:
Galena Summit and Eastern Mtns
Location:
Fourth of July Drainage (6,800-9,700', most aspects)

Signs of Unstable Snow

Recent Avalanches? 
Yes
Cracking? 
Isolated
Collapsing? 
Isolated
Unsure on timing of recent-ish slides, probably a bit older than 48 hours. I experienced collapsing and associated cracking in many areas I traveled through, but it was not continuous through my tour. In places, slopes did not collapse until my second pass as I returned on the skin track.

Snow Stability

Stability Rating: 
Fair
Confidence in Rating: 
Low
Stability Trend: 
Steady

Bottom Line

This was our first trip into this area this year. I observed evidence of widespread avalanche activity that likely occurred during the 12/1 avalanche cycle, as well as a few large avalanches that likely occurred 12/4 or 12/5 with additional snow and wind. A very weak snowpack exists in this area, similar to what has been observed across our forecast area.

Advanced Information

Weather Summary

Cloud Cover:
Clear
Wind:
Moderate , W
New/Recent Snowfall:
A little tough to be certain, since we don't have a baseline here yet, but looked like 15cm since 12/4

Clear skies and moderate westerly winds in the White Clouds today, moving small amounts of snow around. Clouds were building in from the south and west throughout the day, limiting solar radiation in the Sawtooths/W Smokys/Banner areas and the Boulders later in the day.

Avalanche Observations

 #  Date Location Size Type Bed Sfc Depth Trigger Photos Details
1 Dec 5, 2022
(+/- 3 days) 		Fourth of July
W 9800ft 		D2.5 HS-Hard Slab N-Natural
Crown of a large natural avalanche that was observed in the Fourth of July Creek drainage in the White Cloud Mountains on 12/8. It likely failed on 12/4 or 12/5, during or shortly after a windy storm. Though the crown is not particularly wide, this slide picked up speed and entrained a lot of debris thanks to the nature of the terrain. This slope faces W at 9,800'.
Report
1 Dec 5, 2022
(+/- 3 days) 		Champion Basin
NW 9700ft 		D2.5 HS-Hard Slab 4ft N-Natural Report
3 Dec 1, 2022
(+/- 1 day) 		Fourth of July
NE 9500ft 		D2 SS-Soft Slab N-Natural Report
1 Dec 1, 2022
(+/- 1 day) 		Fourth of July
NE 9400ft 		D2 SS-Soft Slab N-Natural Report
2 Dec 1, 2022
(+/- 1 day) 		Fourth of July
NE 9400ft 		D2 N-Natural Report
25 Dec 1, 2022
(+/- 1 day) 		Fourth of July
NE 8000ft 		D1.5 N-Natural Report
Fourth of July
Champion Basin
Fourth of July
Fourth of July
Fourth of July
Fourth of July

Snowpack Observations

HS=45-55cm along valley floor at mouth of drainage, increasing to 80-90cm as you get further back in the drainage and climb in elevation. 11/27 weak layer is down 45-50cm here, similar to what has been observed in Galena Summit area. However, the slab here is denser, with a 10cm interval of 1F in the middle. This was enough to easily keep me above it when trail-breaking on skis. On the sled I was floating above it unless I hit the throttle or dug a ski in for a turn. The ability of the slab to keep me above the weak layer made collapsing less common than I've seen in other places recently (the day before in E Fork, and the day before that on Titus), but I still triggered some long traveling collapses and felt that the potential for remotely triggering slides was easily on the table and traveled accordingly. I experienced collapsing and associated cracking in many areas I traveled through, but it was not continuous throughout my tour. In places, slopes did not collapse until my second pass as I returned on the skin track. As I motored in on the sled I could see collapses propagating across meadows and shaking snow off trees.

I found a good bit of SH at the 11/27 interface, but the main problem seemed to be the very weak (F-) facets underneath. The weakest portion of this snow was 5cm thick, but it looked fairly ugly below that as well. I also found remnant snow from October storms (this is our 11/1 interface). This snow had fully made the transition to DH, with large cupped and striated crystals. This snow is very weak, but there isn't an obvious interface between this snow and the weak snow above, its just all weak and ugly. At the ground (as observed in other locations that 11/1 exists), there is 3-5cm icy cap on the ground. This was ever so slightly moist where I dug at 8,200' on a N aspect. This pit returned ECTPV and ECTP5, and CPST 12 and 14/100 both to END. All tests failed on 11/27, down 45-50cm.

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
 Weak Layer(s): Nov 27, 2022 (FC)
Comments: Rose shaded based on where this weak layer exists. I expect it is at its worst on NW-N-NE-E but I have no interest in gambling with it on the other half of the compass either. Tough call on sensitivity, but based on time since loading and long-traveling collapses I'd put it somewhere between stubborn and reactive.

"Simple" wind slabs likely exist as a separate problem, but I did not encounter them anywhere that 11/27 didn't exist.