Obs-Snow Profile: Short Swing 12/20/2010

Observer Name:

Greg Gagne/Will Deutschman

Observation Date:

12/20/2010

Region:

Salt Lake
Big Cottonwood Canyon
Mill D North
Short Swing

Location or Route:

Short Swing -> Powder Park

Weather

Sky:

Obscured

Precipitation:

Light Snowfall

Weather Comments:

Virtually no wind at the top of Shortswing. -7 C @ noon. S1 snowfall.

Snow Characteristics

New Snow Depth:

12"

New Snow Density:

Low

Snow Surface Conditions:

Powder

Snow Characteristic Comments:

30 cm settled new and much lighter density than the past few days. Although graupel was present, we were not finding any weak layers within new snow since it began snowing on Friday, so am expecting any instabilities within the new snow to have settled out (not surprising given the warm temps and dense snow.) New snow is sitting on rain and temperature crust < 8000'

Red Flags

Red Flag Comments:

There were no obvious red flag signs apart from rapid loading of new, high-density snow.

Primary Concern

Primary Concern:

Deep Slabs

Probability:

High

Aspect:

North

Northeast

East

West

Northwest

Elevation:

High

Mid

Trend:

More Dangerous

Primary Concern Comments:

I have been watching the buried rime crust (which is now buried under 60 cm snow at 9500' in mid-BCC) and identified it today on a N-facing slope at 9500'. Stability tests were able to get failures in the faceted snow beneath this layer. I think it is possible to find this rime crust on any aspect other than SE -> SW. First inspection of the pit didn't identify the crust, but I was able to find it sliding the crystal card down through the pit wall. Am rating this hazard more dangerous with increased snow and water content expected. Am struggling with probability rating - probably Considerable in areas with less snow, High in areas with more snow.

Elevation:

9500'

Aspect:

North

Slope Angle:

snow_profile_location:

United States

40° 38' 42.792" N, 111° 37' 45.5988" W

Comments - Photos - Videos (group 1)

Was finding mid-BCC to feel much safer than elsewhere. About 30 cm (12" new) overnight at 9500' with no collapsing or cracking. Was finding the 2 weak layers (near-surface facets and facets below the rime crust) to be reactive with tests today, but the faceted layer below the rime crust took 30 taps (the 10th tap from the shoulder) for the slab to propagate across the column. The near-surface faceted layer only took 15 taps (the 5th tap from the elbow), but the fracture did not propagate all the way across the column. So overall, pretty good stability scores. But wasn't crazy about the structure (slabs sitting atop weak faceted layers), the widespread reports of avalanching since Sunday, and the rapid increase in water weight to the snowpack = proceed cautiously while using gentle terrain. Am calling the hazard outside of wind-loaded areas in mid-BCC as solid Considerable (Level 3), and High elsewhere (Level 4). But it was pretty safe where I was traveling and doesn't provide much evidence as to conditions in more prominent avalanche terrain.

Snow Profile Location

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