Surface instabilities in the Sherwins

SNOWPACK OBSERVATION
Mammoth rock
Submission Info
Forecaster
Saturday, December 7, 2019 - 2:15pm
Red Flags: 
Whumphing noises, shooting cracks, or collapsing
Recent loading by new snow, wind, or rain
37° 36' 37.5372" N, 118° 59' 32.9604" W
Snowpit Observations
More detailed information about the snowpack: 

We went for an afternoon tour up Sherwin ridge this afternoon to get a sense of how the new snow and strong winds are affecting the snowpack.  Leaving the car at the Mammoth rock trailhead a little after 12, the temperature was right around 30°F, and heavy wet snow was falling.  Touring up towards Mammoth rock, it was immediately evident that the new snow came in relatively wet and dense, resulting in an upside-down feel to the surface snow. We observed snow totals of about 20cm of 4f/F up to our high point at 9800’.  While the surface snow was reactive to hand sheers and kick turns tests, we did not observe any significant cracking during our tour, nor did we see propagation in our ECT Test. I don’t think it will take too much more snow before storm slabs become more reactive.  On this note, I was able to confirm that much of the Surface hoar I observed yesterday is still intact below the new snow, even in more exposed areas.  I did not find any above 8800’ or so, and we have not received any reports of its presence outside of the Sherwins. However, it will be worth investigating as the presence of buried surface hoar will make storm slabs more sensitive as they continue to develop. 

We also observed ample evidence of wind loading throughout the tour, including pretty extensive drifting and some sensitive shallow wind slabs in exposed areas and cross-loaded features. We opted to descend before reaching the ridge due to the gale-force winds and the risk of more substantial wind slab.  

Snowpit or crown profile photo or graph: 
Snowpack photos: 
Weather Observations
Blowing Snow: 
Yes
Cloud Cover: 
100% of the sky covered by clouds
Air temperature: 
Below Freezing
Wind Speed: 
Strong
Precipitation: 
Snow
Air temperature trend: 
Cooling
Wind Direction: 
South
Accumulation rate: 
Less than 1 in. per hour
More detailed information about the weather: 

Snow continued throughout the afternoon and the temperature seemed to be on a cooling trend.  High winds were prevalent throughout the afternoon and locally they were shifting around the rose.  Significant snow transport was observed on the ridge suggesting the prevailing winds were coming out of the south/southwest.

-- placeholder --

ESAC receives significant financial support from ...