Observation: White Pine

Observation Date
12/6/2019
Observer Name
Bruce Tremper
Region
Salt Lake » Little Cottonwood Canyon » White Pine
Location Name or Route
White Pine to upper cirque
Weather
Sky
Clear
Snow Characteristics
New Snow Depth
2"
New Snow Density
Medium
Snow Surface Conditions
Powder
Snow Characteristics Comments
Just a couple inches of new, relatively dense snow on top of the heat crust from a couple days ago. It actually skied pretty well despite feeling the variable heat crust just below the surface. Sheltered and shaded slopes are the best, as usual. Coverage is quite good with no fear of hitting rocks or stumps with about a meter of dense snow around 8,000' and a bit more than a meter around 9,000'
Red Flags
Red Flags
Poor Snowpack Structure
Avalanche Problem #1
Problem
Persistent Weak Layer
Trend
Decreasing Danger
Problem #1 Comments
Unfortunately, there are still monsters in the basement. I could feel the distinct depth hoar layer near the ground on most every northwest through east facing slope above about 8,000' every time I turned my pole upside down and shoved it into the snow. Most of the steep, shaded slopes appear to have slid to depth hoar during the big storm. You can see filled-in fracture lines on most every slope with rumpled-up and piled-up debris below but they are all covered by quite a bit of subsequent snow, so they are subtle to see. I could not see any previous avalanche activity in the upper elevation, above-tree-line terrain because so much of it has filled in with wind blown snow but I bet a lot of that terrain also slid during the storm.
I dug a quick snow profile on a north facing slope at 9,300'. I got several isolated columns to fail on 12 taps, (easy taps from the elbow) popping out pretty easily on the depth hoar near the ground. On an extended column test, I got it to propagate on the depth hoar layer with 15 taps (medium taps from the elbow). Total snow depth is 150 cm with a fairly stout, 1-finger slab above the weak layer. So things are still sketchy and I strictly avoided any slope steeper than 30 degrees that faced the north half of the compass. It's late so I'll try and turn in a snow profile diagram tomorrow.
Although most slopes seem to have slid already, I'm sure many have not. And the poor snowpack structure I saw with the easy collapses and propagations I saw in the snow profile, I would continue to call it Considerable on the shady slopes above about 8,000'. Avalanches will break 2-3 feet deep to the ground. Perhaps difficult to trigger because of the stout, overlying slab but very large if you do.
Comments
On the first two photos you can see subtle signs of avalanche activity during the Thanksgiving storm, which have been obscured by new snow. Most every steep slope in the drainage I could see seemed to have slid during the Thanksgiving storm. I could not tell if any of the very upper elevation, above-tree-line slopes had slid because they had a lot of subsequent wind damage.
On the third photo, there's a few ski tracks on the shoulder of Birthday Chutes on a wind loaded roll above trees, which looked like a pretty bold line for the poor snowpack structure we have. But in general, we only saw ski tracks from perhaps 3 people who ventured into upper White Pine.
Today's Observed Danger Rating
Considerable
Tomorrows Estimated Danger Rating
Considerable