Observation: Cottonwood Canyons

Observation Date
01/7/2018
Observer Name
Greg Gagne/Mark Johnston

Region:

Location Name or Route
Upper LCC/BCC Perimeter
Weather
Sky
Clear
Wind Direction
West
Wind Speed
Moderate
Weather Comments
Gusty winds along upper ridge lines.
Snow Characteristics
New Snow Depth
3"
New Snow Density
Medium
Snow Surface Conditions
Powder
Wind Crust
Damp
Snow Characteristics Comments

Small pockets of fresh wind drifts found along upper ridgelines. These drifts were sensitive and were 10-20 cms (4-8") thick, but not very widespread and only propagate 3-5 meters (10-15')

Solar aspects were getting somewhat damp when exiting at 1 pm, with small rollerballs on steeper south and west aspects.

Small amount of new snow had enough body to it to greatly improve ski conditions!

Red Flags
Red Flags
Recent Avalanches
Cracking
Poor Snowpack Structure
Comments

Despite upwards of 0.7" of water weight in upper LCC, as well as some fresh wind drifting, the Saturday storm does not seem to be enough to affect deeper buried layers. The new snow/old snow interface is the weakest snow with a poor bond between the layer of near-surface facets that formed on top of the old snow surface (this formed during the period of high pressure from 12/26 - 1/5) and the small (5-10 cm/2-4") storm slab of denser snow that fell on Saturday. 

There was also a period of wind Saturday and into Sunday morning, creating some denser drifts. 

The photo below is one such fresh wind pocket I found on an east aspect at 10,000'

While out on Saturday in the Brighton backcountry with UAC colleagues Andrew Nassetta and Craig Gordon, we were getting the cracking and propagation of shallow storm slabs (~5 cms) failing at this interface. The slab was denser snow, but so shallow it was generally harmless. However, it was a clear indication the layer of facets on top of the old snow surface was preserved, and it may become a very active weak layer with more snow anticipated about midweek.

Still getting some cracking on Sunday morning, but for the most part could only get activity where there had been some wind-drifting creating a denser and thicker slab.

The video below is my partner Mark Johnston demonstrating a shovel tilt test. This is a useful technique for testing the interface of the old snow surface with new snow and/or wind. As can be clearly seen, very easy to get clean shears at the interface. While not that much a concern for now, it may become reactive with additional loading. 

 

Video
Today's Observed Danger Rating
Moderate
Tomorrows Estimated Danger Rating
Moderate
Snow Profile Coordinates