Observation: Bear Trap

Observation Date
2/27/2021
Observer Name
John Lemnotis
Region
Salt Lake » Big Cottonwood Canyon » Bear Trap
Location Name or Route
Beartrap
Weather
Sky
Broken
Precipitation
Moderate Snowfall
Wind Direction
Northwest
Wind Speed
Light
Weather Comments
Sky coverage was in and out today with brief periods of sun, mostly overcast or obscured keeping the storm snow dry on all aspects we touched today include mid elevation south. Snow was steady from our start at 0700 though 1500 ranging from the lows of s-1 to as great as s2 for brief periods. Winds were as forecasted at the mid elevations we traveled through loading SE aspects mostly.
Snow Characteristics
New Snow Depth
10"
Snow Surface Conditions
Powder
Snow Characteristics Comments
At 0700 at 9600' in BCC there was about 15-20cm of low density storm snow on the ground that covered mostly unsupportable crusts. Ascending to 9600 N facing terrain was bottomless with very deep trail breaking and S facing slopes have 25cm of storm snow. North was well behaved with no cracking observed, storm snow bonding well to the old surface in hand pits, and not yet forming a slab. S aspects were slightly more cohesive, minimal cracking, and bonded poorly where stout crusts were present. Anything that held a fresh wind load was sensitive, would crack, and felt very slabby.
Red Flags
Red Flags
Recent Avalanches
Heavy Snowfall
Wind Loading
Cracking
Poor Snowpack Structure
Red Flags Comments
We have a lot of red flags present today and that will be the trend for tomorrow. The storm snow will still be active and there is plenty of snow to be transported but even light winds. Throw the PWL in the mix and there is a possibility of step down avalanches and repeaters. Now is not the time to throw caution to the wind.
Avalanche Problem #1
Problem
Wind Drifted Snow
Problem #1 Comments
Today's primary concern was wind drifted snow. Active loading was easily visible on ridelines and you could certainly feel it as well. NE-E-SE were the most effected in the area we traveled today with wind triggering a small natural in W willow on a S aspect (SS-N-D0.5 I) pictured below. Cracking easily observed if you skinned on or near freshly loaded terrain.
Avalanche Problem #2
Problem
Persistent Weak Layer
Trend
Same
Problem #2 Comments
PWL is still widespread in the forecasted area. We dug on a SE aspect at 9640' near W willow to inspect basal facets. HS 215 with fewer than expects crusts mid pack, a stout 1F slab more than 1m thick in the center of the pack capped the 1F-4F basal facets that were about 10cm thick and they were wet. You could make a solid snowball with these grains. This is just one data point and I would not say it is completely representative of the entire ranch for that aspeect and elevation through it did bring a smile to our group. Another hole at 9600' NE in W Willow showed an HS of 215cm. The basal facet layer was 45cm thick, dry, and grains were about 2mm. I decided to do a hybrid ECT to show the group the consequences of triggering a slide on this layer (video posted below) Deep ECTpM on faceted grains down 170cm. We also did a PST yielding PST 120/170 END down 170 on faceted grains. This is a low likelyhood high consequence scenario. We still have poor structure and structure trumps strength every time.
Video
Today's Observed Danger Rating
None
Tomorrows Estimated Danger Rating
None