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Observation: Cottonwood Canyons

Observation Date
4/3/2019
Observer Name
Greg Gagne
Region
Salt Lake » Cottonwood Canyons
Location Name or Route
Upper LCC/BCC Perimeter
Weather
Sky
Obscured
Precipitation
Light Snowfall
Weather Comments
Very obscured with poor visibility. Rain/snow line was ~7500'
Snow Characteristics
New Snow Depth
4"
New Snow Density
High
Snow Surface Conditions
Powder
Damp
Snow Characteristics Comments
Storm snow settled out to 10 cms. Green housing occurring by early afternoon, combined with sun peeking through, dampened all aspects other than due north > 9,500' (likely even higher.)
Red Flags
Red Flags
Recent Avalanches
Red Flags Comments
Was seeing small, wet loose slides on southerly aspects around 3 pm. Otherwise was able to trigger several wet loose, and shallow wet slabs as described below.
Avalanche Problem #1
Problem
Wet Snow
Trend
Increasing Danger
Problem #1 Comments
Greenhousing and sun dampened the new snow, making it reactive to stability tests . Much of it was minor, but slides were running on old crusted snow surface, and therefore were running rather fast for wet slides. Wet slides did required slopes steeper than 40 degrees to get moving. These were both wet-loose and well as shallow wet slabs. They were 10-15 cms (4-6") thick, running on the old crust interface. Debris piles were up to 120 cms (4'). The widest was 40' wide, but most were only 10-15' wide. With some sun and warm temperatures forecasted, these should be even more widespread on Thursday. I think the only areas that will be immune from wet activity for Thursday will be upper elevation (> 9500') north-facing.
Photo below shows debris on uphill side of trees, up to 120 cms (4') deep.
Video of wet activity:
Video showing the debris
Comments
Was also finding a poor interface with storm snow and old snow surface on north aspects above 10,000'. The photo below shows the clean shears on this interface using a shovel tilt test. (Not identifying any facets, just the lower-density stellars were bonding poorly to the old snow surface.) I was not getting any propagation in the slab (but I did see an observation as well as Instagram post of some cracking in new storm snow), and I think this issue will have likely settled out by Thursday.
Video showing ski cut producing shallow, wet snow avalanche running on old crusted, snow surface:
Wet debris at the base of the Y Couloir
Today's Observed Danger Rating
Moderate
Tomorrows Estimated Danger Rating
Moderate