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Observation: Sunset Peak

Observation Date
5/3/2018
Observer Name
B
Region
Salt Lake » Big Cottonwood Canyon » Sunset Peak
Location Name or Route
Catherines Area: Rocky Points/Sunset
Weather
Sky
Broken
Precipitation
Light Snowfall
Wind Direction
North
Wind Speed
Moderate
Weather Comments
Early morning start with the skies initially clear, and then by 0930 the clouds began to fill in. Tempertures rose rapidly, and even with the skies broken the intense May sun combined with mid 30's at the 9500 plus to dampen even the northerly facing aspects with slope angles <30 degrees by 1030. Easterly and southerly aspects had roller balls as early as 0900. By 0900 the moderate NW winds veered more to be out of the direct N, and wind blown and or transport was moderate and observed on mid slope features as well as at the upper ridgelines. At 1130 there was a quick squall that moved through dropping a trace of graupel.
Snow Characteristics
New Snow Depth
8"
New Snow Density
Medium
Snow Surface Conditions
Powder
Dense Loose
Wind Crust
Melt-Freeze Crust
Damp
Snow Characteristics Comments
The 2 to 4 inches of snow that fell on Tuesday was very dense and appeared to have fallen as damp grains and served as a great spongy base. Then the PI ramped up around 1700 on Tuesday evening, and continued with S2 rates until 2000 and dropped another 5 to 8 inches of medium density snow, with another brief shot in the early morning hours. HST ranged from 5 to 10 inches depending on location and elevation with the upper BCC zone in the Catherine Basin area getting the Lion's Share. The riding was good in dense spring powder and even some of the snow that got damp rode well in the upper elevations. Lower elevations were getting sticky on the low angle by 1100.
The previously cited winds were creating upslope and cross loaded soft/shallow wind slabs. Minimal cracking in these wind slabs were observed; and by the end of the morning hours variable riding conditions were being created. North and NW facing slopes in the upper alpine were getting striped in many locations. and all aspects were getting damp besides due N wit angles 30 degrees and greater.
Red Flags
Red Flags
Recent Avalanches
Wind Loading
Cracking
Rapid Warming
Poor Snowpack Structure
Red Flags Comments
Poor snowpack structure limited to density changes in the new snow. Hand shears were indicating an obvious easy weakness at the interface from the dense snow from Tuesday to the lighter density snow that fell later in the day. See picture below of wet loose avalanche that made efforts at propagaing to a wet slab on an easterly facing slope, and the bed surface for this small natural was the above cited interface. Minimal cracking in mostly unreactive shallow/soft wind slabs. Wind loading was occurring and the highest elevations with a possibility of wind slabs that may have been more sensitive in the afternoon hours once they were receiving more intense solar.
Avalanche Problem #1
Problem
New Snow
Trend
Decreasing Danger
Problem #1 Comments
See above for the previously cited problem interface, and with the warm tempertures on Wednesday, this problem interface may have yielded more activity in the afternoon hours. The winds appeared to be serving as a contributing factor enhancing this storm slab issue in many locations in the exposed upper alpine. All that said, once the temperatures cool off later in the day and through the evening these problem issues most likely will decrease and or vanish by Thursday.
Avalanche Problem #2
Problem
Wet Snow
Trend
Decreasing Danger
Problem #2 Comments
Widespread wet loose activity and roller balls observed from 0900 on. Of note, a group of skiers riding the steep easterly facing terrain in the Rocky Points area were easily triggering small wet loose slides. As the sun moved around the compass this issue obviously appeared to travel with it into the afternoon hours.
See picture below, and in particular the right flank of this small wet loose. This slide tried to propagate into a wet slab, but the slope angle let up. This slide occurred at 1045 and was on an easterly aspect at 9800 feet and was initiated by roller balls coming off the rocks above it.
Today's Observed Danger Rating
Moderate
Tomorrows Estimated Danger Rating
Low