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Observation: Big Cottonwood Canyon

Observation Date
12/15/2024
Observer Name
B
Region
Salt Lake » Big Cottonwood Canyon
Location Name or Route
Upper Big Cottonwood Canyon
Red Flags
Red Flags
Heavy Snowfall
Wind Loading
Cracking
Collapsing
Poor Snowpack Structure
Red Flags Comments
Day began with a quick moving frontal passage at 0630 that delivered another 7 to 10cm of Graupel. HST in the Brighton area 50cm. A combination of the yesterdays warm pm and overnight temperatures with this latest round of precipitation created a significant density inversion in the upper snowpack. The Westerly winds were active in the early morning hours, but they appeared to die down considerably by 1000 hours. Still, there was Moderate Wind Blown and or Transport observed at the Mid and Upper elevations at times even in the early afternoon hours. Widespread Cracking in this newly developed Upper Snowpack Slab was observed on many steep slopes. Muffled Collapsing was also observed. The pre-storm widespread Poor Snowpack Structure contributed to easily triggered Soft Slab Avalanches that were Reactive and shearing on test slopes at the old snow/new snow interface with the weak layer being 1 to 2 mm facets.
Avalanche Problem #1
Problem
Persistent Weak Layer
Trend
Same
Problem #1 Comments
It appears that there is a potential 30 to 45cm slab that is now beginning to overburden our weak snowpack. 4 Finger plus to 1finger slabs may now be found on many aspects in the Upper and Mid elevations. Wind has been a contributing factor in some locations (especially in the more exposed Upper elevations}, yet the previously cited density inversion is also playing a role in this issue. SWE values from the storm barely hit the critical mark, and many slopes are still exhibiting Stubborn/unreactive qualities.
Avalanche Problem #2
Problem
New Snow
Trend
Decreasing Danger
Problem #2 Comments
Widespread Loose Dry was observed in steep cliff band locations; and the previously cited density inversion also helped create sensitive/reactive Storm Slab issues 15cm down. Both these issues will likely be less reactive in the next 24 hours.
No Natural Slab activity was observed during the afternoon when the skies were clearing. As a result the Danger appeared to be Consequential Moderate with the potential to trigger avalanches in Steep Terrain, especially in those areas that have received any kind of Wind Loading to make the newly formed overlying Slab more cohesive.
Snow Profile
Elevation
8,700'
Today's Observed Danger Rating
Moderate
Tomorrows Estimated Danger Rating
Moderate
Coordinates