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Observation: Big Cottonwood Canyon

Observation Date
4/27/2017
Observer Name
B
Region
Salt Lake » Big Cottonwood Canyon
Location Name or Route
Upper Big Cottonwood
Weather
Sky
Overcast
Precipitation
Heavy Snowfall
Wind Direction
Northwest
Wind Speed
Strong
Weather Comments
The skies vacillated between Obscurred and Overcast for the majority of the day with a brief period of Broken around 1600. WNW winds were Strong and even getting down into the mid elevation terrain. Wind Blown and or Transport was Intense, and loading was occurring more well down off the upper ridgelines. Temperatures above 9000 feet were in the low 20's.
Snow Characteristics
New Snow Depth
12"
New Snow Density
Medium
Snow Surface Conditions
Dense Loose
Wind Crust
Melt-Freeze Crust
Damp
Snow Characteristics Comments

Widespread wind damage, and the only location where consistent undisturbed snow was found was in protected terrain on NW, N and NE aspects. Southerly facing aspects were holding cold snow as late as 1400 above 9300 feet. After 1400 conditions changed with E and S aspects got damp, and due to the residual heat in the snowpack this problem was exacerbated below 9300 feet. In this zone except on NNE, N and NNW aspects the snowpack was wet at least 18 inches down. '

New snow from overnight until 0900 appeared to be at least 7 inches, and at least S3 snowfall rates were occurring until 1330. At 1900 snow has resumed and is now falling at S2. The snow that fell overnight was predominantly graupel, and during the late morning hours there was a two hour period of Light density snow.

Red Flags
Red Flags
Heavy Snowfall
Wind Loading
Red Flags Comments
Very little avalanche activity observed today. The only issues appeared to be in the top 2 to 4 inches and where Loose Dry and Loose Wet were a minimal concern. Slope cuts on steep slopes were yielding manageable sluffing in cold dry snow. There was one period when the sun came out for only 15 minutes and a steep SE facing slope yielded an isloated Wet Loose avalanche, and this did not entrain significant snow. The primary concern today was due to the previously cited winds. With their intense velocities, sublimation appeared to be occurring in the most exposed upper elevation terrain. One finger stubborn and unreactive wind slabs were observed in areas down off the ridgelines that were receiving significant wind loading. The sensitive layers from Tuesday at the interface to that melt freeze crust were not reactive today.
Avalanche Problem #1
Problem
Wind Drifted Snow
Trend
Increasing Danger
Problem #1 Comments

See above; and regardless of not finding sensitive wind slabs in the terrain traveled, it is highly likely that there were areas of isolated wind slabs from cross and top loading on steep terrain on SE, E, and NE aspects.

With the forecast for the winds to remain in the critical range, and this combined with significant snowfall, this problem may actually become more widespread and a problem of concern on Friday.

Todays Danger appeared to be Moderate, and with the continuing winds and any significant new snow it may escalate to Considerable on Friday.

Avalanche Problem #2
Problem
New Snow
Trend
Increasing Danger
Problem #2 Comments

This problem may become more of an issue on Friday with any areas receiving significant new snow, and the graupel from Thursday may serve as a reactive weak layer.

Today's Observed Danger Rating
Moderate
Tomorrows Estimated Danger Rating
Considerable