Join us at our 2nd Annual Blizzard Ball
Ad
The National Forest Service Logo
icon-add Observation
Forecasts
Logan Ogden Salt Lake Provo Uintas Skyline Moab Abajos Weather Archives How to read the forecast
Observations & Avalanches
Submit Observation Observations Explorer All Observations Avalanches Fatalities Weather Place Names Map Archives
Education
Avalanche Class List UAC Class List Online Classes Resources and Tutorials Avalanche Awareness Develop Skills
Events
Store
About
Contact Who we are Core Values Staff Board of Directors Past Forecasters Sponsors Annual Reports Sign In
Blog
icon-add Observation
Donate / Join

Observation: Park City Ridgeline

Observation Date
12/23/2020
Observer Name
Greg Gagne
Region
Salt Lake » Park City Ridgeline
Location Name or Route
Park City Ridgeline via Guardsman
Weather
Sky
Few
Wind Direction
Northwest
Wind Speed
Moderate
Weather Comments
Clearing skies as the day progressed. Moderate gusts of wind out of the NW that were drifting well-down off of ridgelines.
Snow Characteristics
New Snow Depth
6"
New Snow Density
Low
Snow Surface Conditions
Powder
Wind Crust
Melt-Freeze Crust
Rain-Rime Crust
Snow Characteristics Comments
15-20 cms very-low-density new storm snow. Some fresh drifts noted both along the ridges and down off of ridges, however, they were not sensitive. Very likely that drifts from very strong SW/W winds were covered by the fresh snowfall.
Was finding rime crust from Sunday afternoon present on predominantly west aspects, with facets and preserved stellars underneath. (Mark Staples was also noticing these same weaknesses underneath the crust in LCC.) Widespread temperature crust on most every aspect as well. Storm snow seems well-bonded to crust, but will keep facets underneath the crust in mind going forward.
On some north-facing slopes > ~9500' was not finding a crust, but preserved near-surface facets from cold and clear temperatures this past Saturday into Sunday, down 15-20 cms. Was able to get clean shears on this layer with shovel-tilt test.
Red Flags
Red Flags
Recent Avalanches
Wind Loading
Collapsing
Poor Snowpack Structure
Red Flags Comments
Despite jumping around on lots of suspect slopes, got relatively few collapses today. But the poor snowpack structure dominates conservative decision making in avalanche terrain.
Avalanche Problem #1
Problem
Persistent Weak Layer
Trend
Same
Problem #1 Comments
Some incredibly weak snow underneath recent storm slabs from 10,420' north and west along the Park City ridgeline. Depth-hoar, and near-surface facets. Dug several pits today, and all were ECTN with Q2/Q3 results. On a north aspect at 10,000' with ECTN results, performed Propagation Saw Test and got the full 100 cm column to fracture on the buried layer of near-surface facets from November/December (Drew's NFL layer) that was down 30 cms on this slope. This is indicative there is a cohesive slab on top of this weak layer. PST 25/100 End down 30 cms.
Comments
Less-reactive snowpack today, and was surprised given the recent strong winds and quick load of ~0.50" of water weight. Fewer collapses and could not get one ECT to propagate. But am focusing more on the poor structure than on any evidence of increasing stability and am continuing to avoid being on, underneath, or adjacent to slopes steeper than 30°. There is a well-connected slab on top of very weak snow underneath, and all we have to do is get a fracture on one part of the slope for it to all release.
Photo of plumes from NW winds along upper elevation ridgelines, and video of wind-drifting and cross-loading in Scott's Bowl along Park City ridgeline.
Video
High or Considerable danger? I had looked through the same data this morning as Trent did in his forecast, and agreed with his morning forecast of a High danger at the upper elevations. After my tour today ("backcasting") I felt the danger was Considerable, and not High. But it has little difference: I continue to avoid avalanche terrain.
Today's Observed Danger Rating
Considerable
Tomorrows Estimated Danger Rating
Considerable
Coordinates