Observation: Catherine's Pass

Observation Date
11/24/2018
Observer Name
Greg Gagne
Region
Salt Lake » Little Cottonwood Canyon » Catherine's Pass
Location Name or Route
Catherine's Pass Area/Rocky Point
Weather
Sky
Obscured
Precipitation
Moderate Snowfall
Wind Direction
West
Wind Speed
Strong
Weather Comments
Persistently strong winds that were blowing in all directions as it was being channeled by terrain.
Snow Characteristics
New Snow Depth
16"
New Snow Density
Medium
Snow Surface Conditions
Powder
Wind Crust
Snow Characteristics Comments
Really difficult to determine new snow amounts as so much snow was being moved around by the winds. Winds made Saturday storm snow much denser with an inverted feel.
HS ranging from 45-100 cms (18-40").
Red Flags
Red Flags
Recent Avalanches
Heavy Snowfall
Wind Loading
Cracking
Collapsing
Poor Snowpack Structure
Red Flags Comments
Numerous bulls-eye clues today with widespread cracking and huge collapses. Wind drifting with sensitive wind drifts. Evidence of either a natural or human-triggered slide in So Long area of Catherines, as well as large repeater in Rocky Point (reported under an avalanche observation.) Weak layers were either density change within recent storm snow or facets.
Avalanche Problem #1
Problem
Persistent Weak Layer
Trend
Same
Problem #1 Comments
Heavy snow amounts plus strong winds clearly overloading persistent weak layers.
Avalanche Problem #2
Problem
Wind Drifted Snow
Trend
Decreasing Danger
Problem #2 Comments
Sensitive drifts found on all aspects above 9000'. On aspects facing generally northwest through southeast, it will continue to be an issue as these drifts are on top of very weak faceted snow. On other aspects, I imagine they will settle out quickly.
Comments
Very intense, sustained winds blowing above 9000' made for dangerous avalanche conditions today, particularly on slopes with weak faceted snow underneath. The dense, wind-blown snow was quite supportable (ski pens were 5-10 cms) and my concern is this new slab will gain strength, and make those slopes with persistent snow at the base "feel" stable. (But in reality it now will just be harder to trigger avalanches, and that any avalanches will just now be larger.)
Photo below is from Rocky Point, an apparent natural avalanche that connected across ~250'. Mark White had reported slides on this slope on Thanksgiving, and this slope was re-loaded with storm and wind-blown snow. It failed on a layer of facets sitting above the October crust. I submitted this under a separate avalanche observation. Take home for me was that slopes with persistent weaknesses that have avalanched have just re-loaded and are primed for more avalanching.
Video
Although I did not ride south-facing slopes, I did talk to a few parties that were on the south aspects around Michigan City in Grizzly Gulch and they reported the storm snow is supportable and is covering up many of the rocks. With continued danger due to weak facets on slopes facing west through southeast, we may have options for much safer riding on south and southwest aspects.
Today's Observed Danger Rating
High
Tomorrows Estimated Danger Rating
High