Collapsing, shooting cracks and poor structure on the NE side of McGee

SNOWPACK OBSERVATION
Mcgee Mountain
Submission Info
Forecaster
Friday, January 24, 2020 - 10:00am
Red Flags: 
Whumphing noises, shooting cracks, or collapsing
37° 34' 11.442" N, 118° 48' 9.306" W
Snowpit Observations
More detailed information about the snowpack: 

Observations indicating significant collapsing on the East side of McGee Mountain came in yesterday afternoon (01/23), and I decided to head up this morning to get a look at the area. Leaving the truck at 8:30 this morning skies were partly cloudy, temperatures were just above freezing, and winds were moderate out of the west. I observed some flagging on ridgetops and even some mid-slope features in Esha canyon and on Nevahbe ridge, indicating stronger winds at higher elevations. 

I started my ascent from McGee creek rd on thin but supportable snowpack weaving between the sage brush.  Surface conditions at this elevation consisted of a 1.5-2 cm melt-freeze crust. At about 8500’ as the slope steepened surface conditions improved consisting of 20 cm or so soft snow on top of an older Supportable crust. Overall the snow cover on McGee is variable with many dry patches on exposed terrain features and ribbons of snow connected enough to link a long run together. 

At approximately 9100’ I felt a significant collapse under my feet, which initiated a shooting crack about 50’ in length. The wumph was loud, I felt the ground shift, and while the crack was not very wide, it ran a relatively long way. Digging in at this location, I found a total height of snow of 60cm and poor structure similar to what has been observed throughout the range. Stability tests highlighted the layer of concern about 25 cm from the surface consisting of a Pencil hard crust resting on top of Fist hard facets. Compression tests broke under moderate load and showed sudden collapse characteristics. (CT15-SC) I conducted two Extended column tests, neither of which produced propagation but both highlighting similar fracture character. (ECTN15) I also did a Propagation saw test, which propagated after 20 cm of cut. (PST20/100 END) See my pit profile for more info.

We have been talking a lot about the poor structure present throughout the range, and my findings today suggest that in some areas, the circumstances may be right to produce an avalanche on these buried weak layers.  In this location, I believe the variable snowpack depth and crust thickness was a net benefit because it limited the extent of the potential slab. I believe if the snowpack was more uniform and the slab more contiguous, this collapse could very well have resulted in an avalanche. 

Snowpit or crown profile photo or graph: 
Snowpack photos: 
Snowpit videos (tests, etc): 
Weather Observations
Blowing Snow: 
Yes
Cloud Cover: 
50% of the sky covered by clouds
Air temperature: 
Above Freezing
Wind Speed: 
Moderate
Precipitation: 
None
Air temperature trend: 
Warming
Wind Direction: 
West
Accumulation rate: 
None
More detailed information about the weather: 

scattered clouds persisted throughout the day with warm temperatures and moderate mid-slope winds. flagging on nearby high-elevation terrain suggested that the winds were much stronger up high. I descended around noon and by the time I got to the car the winds seemed to have dropped significantly.  

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