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PROFESSIONAL OBSERVATION FORM
 Start Date: 02.12.19 Name: Davis Operation: SAC
 Drainage/Route:  Johnstone Observed Terrain:  6500-8000, All Zone/Region:  Wood River Valley
WEATHER OBSERVATIONS
 HN24: HST: 20-30 cm Sky: OVC Precip: Temps:
 Ridgeline Wind: Calm
 Blowing Snow: None Snow Available for Transport: Small amounts
 Comments: Thin, hazy clouds but no direct sunshine. Clouds increased later in the afternoon. Much warmer than yesterday, kicking off mini roller balls in the skin track on steep souths.
AVALANCHE OBSERVATIONS
 No. Location Date Size Type Trigger Aspect Elevation Comments
 4 Hyndmann Ck Within past week 2 N NW 8,500' Four pockets of persistent slab, hard to tell what they ran on, but based on shallow snow depths where I was it was likely (2/2) or the weaker FC near the ground. It looks like this slope would have been wind loaded through the saddle by SE wind in the last storm.
 1 Hyndmann Ck Within past week 2 N W 9,000'
 Comments: See photos
SNOWPACK OBSERVATIONS
 HS: 60-90 cm between 7000-8000' 
 Upper Pack: 20-30 HST (F) with some 20-40 cm 4F-1F wind slab in exposed terrain.  
 Middle Pack: 2/2 MFcr and FC 
 Lower Pack: Souths were wetted to the ground and refrozen. Norths were F- dry DH. 
AVALANCHE PROBLEM ASSESSMENT
Avalanche Characteristics
Character/Avalanche Problem:
Persistent Slab

Layer/Depth:
70 cm

Likelihood of Triggering
Sensitivity:
Touchy

Spatial Distribution:
Specific
Terrain
  Primary Concern Comments: Basal FC/DH in south-facing terrain up to 8000' was wetted and refrozen and should not be much of a problem in this area. On more shaded slopes, the FC were spooky. Still dry and F- under a stiffer wind slab.
 
Avalanche Characteristics
Character/Avalanche Problem:
Wind Slab

Layer/Depth:
40 cm

Likelihood of Triggering
Sensitivity:


Spatial Distribution:

Terrain
  Problem 2 Comments: Most of the loading in this location occurred from the south.
STABILITY TESTS
 Stability Test Results:
8,000' southeast - ECTX, CPST 45/100 (SF), PST 40/100 (SF)
8,000' northeast - ECTP13, CPST 30/100 (END), PST 30/100 (END)

PSTs performed down 60 cm under 2/2 in FC and DH.
OBVIOUS SIGNS OF INSTABILITY
 Marked with checkmark if observed:
 Collapsing (isolated) Depth: 70 cm  
 Comments: Once I was on a more wind affected ridge at 7,500' I experienced 3 large rumbling collapses that traveled out of earshot.
SNOW STABILITY
 Snow Stability Rating for your observed area: Confidence: HIGH Trend: Steady
 Comments (aspects and elevations of instability, etc): MOD at lower elevations where the snowpack is still thin and broken up by sage.
BOTTOM LINE
 Comments: Basal FC and DH are less concerning on more south-facing slopes where they have been wetted and refrozen. Totally different story at slightly higher elevation and more shaded slopes where the FC and DH are dry and F- which should give us quite a show with any thicker wind blown slab or higher density snowfall.
FILE ATTACHMENTS

190212_Johnstone_47.jpg
Persistent slabs up Hyndman Creek on a N-facing slope @ 8,500'

190212_Johnstone_48.jpg
Hyndman Ck, W-facing, 9,000'