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Observation: Big Cottonwood Canyon

Observation Date
4/5/2020
Observer Name
B
Region
Salt Lake » Big Cottonwood Canyon
Location Name or Route
Upper BCC
Weather
Sky
Overcast
Precipitation
Moderate Snowfall
Wind Direction
Southwest
Wind Speed
Strong
Weather Comments
Little bit of everything, depending on the time of day. Morning started out with Light WSW Winds at Mid and non-exposed Upper Elevations, but by 1130, in the Mid and Upper Elevations, they veered more out of the SW and began accelerating to at least the Strong category (and Intense in many locations). Transport and or Wind Blown was at least Strong. Temperatures remained cool until about the time of the Wind Change, and by afternoon it was warm even at the Upper Elevations. Intermittent snowfall throughout the day ranged from S1 to S3 with a brief period of 5 mm graupel as a short wave came in around 1130. Unfortunately, substantial breaks in the clouds began around 1430.
Snow Characteristics
New Snow Depth
8"
New Snow Density
Low
Snow Surface Conditions
Powder
Wind Crust
Damp
Snow Characteristics Comments
Riding conditions went from: good to bad to worse as the day went on. From 0830 until 1130 the new snow was cold, dry and light above 9200, and the riding was good. In any areas that were receiving any signs of wind, there were 4 finger/soft Wind Slabs. As the Winds were picking up the riding started to thicken up and begin to get slabby. Then the Winds really accelerated and there were widespread 1 finger to pencil hard Wind Slabs even down into the Mid Elevations. Finally, in the early afternoon during periods with breaks in the clouds, greenhousing was dampening the snow surface even on north facing terrain above 10200. And from, 9200 down everything was wet.
Red Flags
Red Flags
Recent Avalanches
Heavy Snowfall
Wind Loading
Cracking
Rapid Warming
Poor Snowpack Structure
Red Flags Comments
It appeared that the initial 2 inches of snowfall overnight came in very light, and then it became upside down with next impulses of snow in the early morning warming temperatures. Hand shears easily identified this weakness in various hasty pits. The aforementioned winds combined with heavy periods of PI created significant slab issues. Upon exiting at 1500, the intense daytime highs and solar appeared to be ready to tip the scales towards widespread damp/wet instabilities on many aspects and elevations; and the pre-storm m/f crusts may have helped provide excellent running surfaces for the damp and wet snow to become reactive on.
Avalanche Problem #1
Problem
Wind Drifted Snow
Trend
Increasing Danger
Problem #1 Comments
See above and avalanche report from THC. Warm temperatures and the Moderate to Strong Winds may help glue some of these potential instabilities into place, but caution may be advised in any steep terrain with recent Wind Loading.
And, special caution may be indicated when near, on and or under any of the large overhanging Cornices...especially during the afternoon hours when temperatures are peaking.
Avalanche Problem #2
Problem
Wet Snow
Trend
Same
Problem #2 Comments
See above, and this may continue to be an issue on Monday.
Today's Observed Danger Rating
Considerable
Tomorrows Estimated Danger Rating
Moderate
Coordinates