Observation: Big Cottonwood Canyon 2/21/2012

Observer Name:

Kobernik

Region:

Big Cottonwood Canyon
Salt Lake

Observation Date:

02/21/2012

Weather

Sky:

Overcast

Precipitation:

Light Snowfall

Wind Direction:

Northwest

Wind Speed:

Moderate

Weather Comments:

Wind let up a bit by mid day, right about the time a nice rime event occurred. Riming was noted in Collins Gulch but not in the Catherines/Dog Lake area. I again noted it up high along Clayton's Peak on the west aspect.

Snow Characteristics

New Snow Depth:

New Snow Density:

Medium

Snow Surface Conditions:

Dense Loose

Snow Characteristic Comments:

Snow was notably deteriorating compared to Monday but still good turning at the end of the day.

Red Flags

Wind Loading

Cracking

Collapsing

Red Flag Comments:

Wind loading was obvious and these fresh drifts would crack easily.

Primary Concern

Primary Concern:

Wind Slabs

Probability:

Considerable

Aspect:

North

Northeast

East

Southeast

Elevation:

High

Trend:

More Dangerous

Primary Concern Comments:

Higher density snow combined with wind produced the hazard today. I noted numerous naturals that most likely occurred early this morning with the new snow and stronger winds. Many shallow soft slabs released in almost all chutes in NE facing Rocky Point. I noted more soft slabs on N facing terrain just above Lake Martha. I was able to remotely trigger a number of soft slabs from the ridge above Dog Lake Chutes.

When remotely triggered slides are happening we usually think of the weak layer as facets or buried surface hoar. However, I looked carefully at the fractures of each avalanche I triggered and found the weak layer to be stellars from Sunday's storm. This is not that common but I do see this type of weak layer a handful of times each winter.

The video below was of the largest slide I triggered which was 6 to18" deep.

snow_profile_location:

Comments - Photos - Videos (group 1)

Video 1:

Comments - Photos - Videos (group 2)

The only activity I observed today was due to the new higher density snow combined with winds and Sunday's stellars acting as the weak layer. I was in terrain that had a deeper overall snowpack than most places, therefore, didn't see any issues with buried facets which exists in many areas, especially the thinner areas. I did not find any buried surface hoar either which I know exists in scattered terrain as well.

With continued wind over the next couple of days, I suspect we should hear about some of these persistent weak layers becoming active.