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ADVANCED OBSERVATION FORM
 Start Date: 04.12.19 End Date: 04.12.19
 Drainage/Route:  Diamond, Lost River, Breitenbach, Donaldson Observed Terrain:   Zone/Region:  Challis/Lost River
WEATHER OBSERVATIONS
 HN24: HST: Sky: Precip: Temps:
 Ridgeline Wind:
 Blowing Snow: Snow Available for Transport:
 Comments: Warming trend occurred during the beginning of last week. Hilts Creek (8000’) reported a high of 56*F on 4/8 (rain line up to 10,500’-11,000’?) then 4-6” (0.5” SWE) of light density snow fell through 4/8-13 with M-S NW winds 4/10-13. Winds were out of the NW on the morning of 4/13 and were on the high side of M pushing plumes and spindrift off the peaks and down into the basins. Overnight lows were in the teens 4/10-13. High solar input the afternoon of 4/13.
AVALANCHE OBSERVATIONS
 No. Location Date Size Type Trigger Aspect Elevation Comments
 1 Donaldson SE bowl Within past week 2.5 HS ASu SE 10,500' 20190413 at 1500hrs. ~18-25cm deep (Ground (~120cm) for persistent slab), 1400’ wide, 2700’ linear, 1300’ vertical to toe of slide. JP slid 787’ vertical, 1350’ linear. Upper crown failed on a March-April Persistent slab, stepped down into basal FC/DH.
 Comments: Many Loose Wet and Dry. Noticed one other similar slide (same aspect/elev) on our exit out of Jones Creek. We found out later that Ben saw a similar slide but on a NE aspect out Cedar Creek and a half dozen other smaller crowns.
AVALANCHE PROBLEM ASSESSMENT
Avalanche Characteristics
Character/Avalanche Problem:
Persistent Slab

Layer/Depth:
18-25cm

Likelihood of Triggering
Sensitivity:
Reactive

Spatial Distribution:
Specific
Where did you find this problem?
  Primary Concern Comments: 
 
Avalanche Characteristics
Character/Avalanche Problem:
Deep Persistent Slab

Layer/Depth:
80-120cm

Likelihood of Triggering
Sensitivity:
Stubborn

Spatial Distribution:
Widespread
Where did you find this problem?
  Problem 2 Comments: Upper elev start zones, where wind loading present and/or MF/FC combo.
 Comments: There are persistent slabs present on many of the aspects at the basal layer in the Lost River Range. Most seem like they need a medium sized loading event or need to be sympathetically released to step down into deeper persistent slab. The weight of a skier doesn't seem like enough to get the N1/4 moving based on our obs and many other parties in the area. But the natural that was seen in Cedar Creek near Borah, demonstrates the possibility of it being a factor. There were a number of other slides reported that looked very similar to the upper crown of the slide we triggered, which leads me to believe this may be more widespread than previously thought.
STABILITY TESTS
 Stability Test Results:
SNOW STABILITY
 Snow Stability Rating for your observed area: Confidence: Trend:
BOTTOM LINE
 Comments: See attached narrative.
FILE ATTACHMENTS

Donaldson Slide (1).pdf
Donaldson Slide Summary

robbie_topo_1___BwOAnSwgmha___.jpg
Location of where skier was carried.

Screenshot_20190416_161539_temp.jpg
Avalanche path.

IMG_20190413_160711.jpg
Crown.

1-IMG954086.jpg
NE aspect Cedar Creek natural