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Observation: Main Porter

Observation Date
12/14/2019
Observer Name
Greg Gagne
Region
Salt Lake » Mill Creek Canyon » Porter Fork » Main Porter
Location Name or Route
Porter Fork
Weather
Sky
Obscured
Precipitation
Moderate Snowfall
Wind Direction
West
Wind Speed
Moderate
Weather Comments
Strong gusts along upper elevation ridgelines. New snow was dense graupel and rimed stellars.
Snow Characteristics
New Snow Depth
8"
New Snow Density
Medium
Snow Surface Conditions
Powder
Wind Crust
Snow Characteristics Comments
New snow is dense and snow totals are very elevation-dependent. HS at 8500 is 100 cms. Above about 9000' there is roughly 30-45 cms (12-18") of dense storm snow. HS at 9600 is 1.5 meters (5')
Red Flags
Red Flags
Recent Avalanches
Heavy Snowfall
Wind Loading
Poor Snowpack Structure
Red Flags Comments
Jumped on several test slopes but was unable to get any cracking or collapsing. Ski cuts in wind-drifted zone would only get small pockets to crack, and not propagate very far. Overall the dense storm snow seemed quite stubborn to initiate with any stability tests.
Avalanche Problem #1
Problem
Persistent Weak Layer
Trend
Same
Problem #1 Comments
Above 8500' there is ~10-30 cms (8-12") of weak, faceted snow down near the ground, with a stout ~1 meter slab on top. Overall the snowpack in upper Porter Fork did not look much different than what I've been seeing in Big or Little Cottonwood canyons.
Avalanche Problem #2
Problem
New Snow
Trend
Decreasing Danger
Problem #2 Comments
ECTs could only get several ECTN's and ECTX's, all breaking unevenly in storm snow density changes in the top 45 cms. The weakest storm snow seemed to be different graupel layers that are present in the top 30-45 cms of the snowpack. The unresponsive ECTs were consistent with the other stability tests (i.e. ski cuts) that showed a stubborn storm slab.
Comments
I also began looking down 45-60 cms for the preserved surface hoar and near-surface facets that Peter Donner was reporting on Thursday (link to obs). In that observation, Donner was finding a poor bond of the initial storm snow to the existing snow surface, which had weakened earlier this past week. I was unable to get any clean shears at this interface, and could not find any preserved surface hoar. The weakest snow I was finding were different density inversions within the storm snow.
The dense show is quite fun to travel on, and the lower-angled slopes are skiing quite well. With great coverage on all aspects, there are plenty of safer riding opportunities on lower-angled slopes.
Am calling the hazard High based upon travel advice of not entering mid and upper elevation northerly aspects.
Today's Observed Danger Rating
High
Tomorrows Estimated Danger Rating
High