Observation: Bear Trap

Observation Date
12/22/2015
Observer Name
Greg Gagne
Region
Salt Lake » Big Cottonwood Canyon » Bear Trap
Location Name or Route
Beartrap Fork
Weather
Sky
Obscured
Precipitation
Moderate Snowfall
Wind Direction
Northwest
Wind Speed
Light
Weather Comments
Weather alternated between periods of Moderate S2 snowfall (~2 cm/hr) and occasional bursts of visibility. Winds were light out of W/NW. No wind transport noted.
Snow Characteristics
New Snow Depth
12"
Snow Surface Conditions
Powder
Snow Characteristics Comments

Storm snow in the past 2 days approaching 60 cms. HS 130 cms (~4.5') at 9500'

Snow that fell during our morning tour was lighter density than what fell overnight.

Red Flags
Red Flags
Recent Avalanches
Heavy Snowfall
Wind Loading
Cracking
Collapsing
Poor Snowpack Structure
Red Flags Comments
Several loud collapses and some cracking in new snow.
Avalanche Problem #1
Problem
Persistent Weak Layer
Comments

Toured in Beartrap Fork today - did not want to venture anywhere close to avalanche terrain.

Several quick pits and pole probes (on storm days I especially find lots of quick ("hasty") pits more meaningful than fewer detailed pits.) Key observations:

- Several weaknesses within storm snow with density changes. Overnight storm snow (~30 cms or 12") sluffing easily on test slopes.

- Unable to isolate a column on some test pits with failures in density changes in storm snow down 30-60 cms (1-2')

- Getting very clean Q1 shears above rime/temperature crust that is now buried anywhere from 45 - 75 cms (18-30") down. There appears to be a layer of weaker snow on top of the crust that has faceted (I was noticing this on Friday when the crust had formed), or just poor bonding to the Sunday storm snow, that is providing the weak layer. Nonetheless, clean/planar shears at this layer.

- Am finding weaknesses in the storm snow - or at the interface of the rime crust - to be the current weakest layers. Stability tests today were getting failures at these layers, and not down at the depth hoar. Am thinking that any avalanche that fails at these layers may step down to depth hoar at the ground. The tricky thing is the rime/temperature crust is supportable enough so that it provides some bridging, which may create even larger avalanches. (Drew pointed this out in Sunday's forecast.)

- Did get to look into Dutch Draw during a short window of visibility and did not notice any recent avalanches. Also looked along West Willow ridgeline (which can often natural) and saw no activity.

Clearly high danger day. Lots of recent snowfall (with significant water weight) and wind loading, loud collapses and cracking. All of this on top of a fragile snowpack. (Not to mention storm snow instabilities.)

Beartrap keeps you on slopes < 30 degrees, and despite difficult trail breaking, we were finding the best ski conditions in quite a few years on these lower angled slopes. Am expecting with overnight snow coming in with even lighter densities, lower-angled slopes will still offer safe skiing and travel conditions for Wednesday.

Sorry for the old-school, text observation. (Did try taking a few photos of quick pits, but they were poor due to snowfall and poor visibility.)

Today's Observed Danger Rating
High
Tomorrows Estimated Danger Rating
High