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PROFESSIONAL OBSERVATION FORM
 Start Date: 12.11.16 Name: Davis, VandenBos Operation: SAC
 Drainage/Route:  McDonald Peak Observed Terrain:  7,200-9,200', N-E-S Zone/Region:  Sawtooth Mountains
WEATHER OBSERVATIONS
 HN24: 4 HST: 22 Sky: BKN Precip: S-1 Temps: 22
 Ridgeline Wind: Light and Gusty from the Variable
 Blowing Snow: L Snow Available for Transport: Large amounts
 Comments: Upper-level flow seemed generally from the west. Observed local wind from the south, west and northwest.
AVALANCHE OBSERVATIONS
 No. Location Date Size Type Trigger Aspect Elevation Comments
 6 McDonald Peak - Sawtooths Within past week 2 SS N 7,500-10,000' All aspects.
 6 McDonald Peak - Sawtooths Within past week 1 SS N 7,500-10,000' All aspects
 2 Gladiator - Boulders Within past week 1 SS N 8,500-9,500' S and SW
 2 Durrance - Boulders Within past week 1.5 SS N S 8,200' Appeared to be small pockets of wind slab, cross-loaded on far lookers left side of the bowl.
 1 McDonald Peak - Sawtooths Within past week 3 SS N 9,300' Multiple aspects NE-SE (photo)
 Comments: Essentially everything that we could see steeper than 35* presented a slab avalanche. Impressive propagation around bowls, groups of trees etc. for a relatively thin PWL at the ground. Poor visibility, but we feel strongly that there were likely many more (possibly larger) avalanches. Many other smaller avalanches throughout Galena Pass and foothills of the Boulders.
SNOWPACK OBSERVATIONS
 HS:  
 Upper Pack: PP and DF 
 Middle Pack: DF and RG (slightly stiffer near the ground) 
 Lower Pack: 5-10 cm of FC/DH 
AVALANCHE PROBLEM ASSESSMENT
Avalanche Characteristics
Character/Avalanche Problem:
Persistent Slab

Layer/Depth:


Likelihood of Triggering
Sensitivity:
Touchy

Spatial Distribution:
Widespread
Terrain
  Primary Concern Comments: All aspects and elevations. Higher confidence at middle and upper elevations.
 Comments: Didn't observe much avalanche terrain at lower elevations.
STABILITY TESTS
 Stability Test Results:
OBVIOUS SIGNS OF INSTABILITY
 Marked with checkmark if observed:
 Cracking (widespread)    
 Collapsing (widespread)    
 Comments: Several loud collapses with visible drop in the snowpack shaking snow off trees 30-40' away.
SNOW STABILITY
 Snow Stability Rating for your observed area: Poor Confidence: HIGH Trend: Steady
BOTTOM LINE
 Comments: I don't believe that natural avalanches were likely, but I wholeheartedly believe that human-triggered avalanches were very likely. The instability was widespread and found on all aspects and elevations >7,500'.
FILE ATTACHMENTS

161211_McDonaldPeak_BV.JPG
Large avalanche on north to east facing aspect of McDonald peak. This crown is over 1500' wide and 1-2' deep.

161211_GladiatorRidge_BV.JPG