Observation: Park City Ridgeline

Observation Date
12/12/2020
Observer Name
Greg Gagne
Region
Salt Lake » Park City Ridgeline
Location Name or Route
Park City Ridgeline via Guardsman
Weather
Sky
Overcast
Precipitation
Moderate Snowfall
Wind Direction
Northwest
Wind Speed
Light
Weather Comments
Snow continued through most of the day, with periods of S1 (1 cm/hr) snowfall. Some gusty N/NW winds along ridges.
Snow Characteristics
New Snow Depth
10"
New Snow Density
Low
Snow Surface Conditions
Powder
Wind Crust
Snow Characteristics Comments
Upper BCC/Park City ridgeline fared quite well with this storm! I was generally finding 15-25 cms of very-low density snow above 9500'.
HS ranges widely, but deeper snowpack areas on northerly aspects have a 75 cm depth.
A few shallow pockets of small wind-drifts along ridgelines.
Red Flags
Red Flags
Cracking
Poor Snowpack Structure
Red Flags Comments
Some minor cracking observed in areas with the most new snow.
Avalanche Problem #1
Problem
New Snow
Trend
Same
Problem #1 Comments
Was able to get sluffing on steeper aspects as well as some minor cracking. The old snow surface is very weak faceted snow, and I was unable to isolate a column with the new snow easily failing at this interface with the old snow surface.
Comments
Even though we only had < 0.5" of water weight from the Friday/Saturday storms, the weak snow at the old snow surface was very reactive to stability tests with very easy shears. The new snow is not yet acting as a cohesive slab, so it is currently only sluffing on steeper slopes. But once the slab begins to sinter (become cohesive) or we add some wind-blown snow or additional storm snow, widespread avalanching on this layer will become more pronounced.
The existing snow prior to the Friday/Saturday storms was quite weak, but there was a fair amount of variability in the structure. In some thinner snowpack areas it was weak and unsupportable, but in some areas where the snowpack was deeper (and probably wind-drifted from strong wind events in mid-November) it is supportable with 4F hardness. Despite the variability, what I am finding in common is that the old snow surface was very weak and this will likely be the initial weak layer as we add more of a load to the snowpack this coming week.
Photo below highlights an area with a generally stronger snowpack (45 cms of 4F+ denser snow at the base), but the darker stripe just above this is the weak, faceted snow surface that was buried underneath Friday/Saturday storm snow.
Low danger at low and mid elevations, Moderate at upper elevations where there are pockets of fresh drifts or greater snow amounts (pushing 30 cms) where the sluffs can entrain more snow.
Today's Observed Danger Rating
Moderate
Tomorrows Estimated Danger Rating
Moderate
Coordinates