Observation: Alta Periphery

Observation Date
2/17/2014
Observer Name
Greg Gagne
Region
Salt Lake » Little Cottonwood Canyon » Alta Periphery
Location Name or Route
Upper Little Cottonwood Perimeter
Weather
Sky
Overcast
Wind Direction
Southwest
Wind Speed
Moderate
Weather Comments
Increasing high clouds as the day progressed. Moderate winds out of the SW that became more sustained by about mid-day. -1C at 9500', though the winds kept temperatures comfortably cool.
Snow Characteristics
New Snow Depth
3"
New Snow Density
High
Snow Surface Conditions
Powder
Wind Crust
Snow Characteristics Comments

Most snow surfaces consisted of 5-10 cms (2-4") of dense snow and graupel that made for excellent traveling and skiing conditions. Some upper elevation (> 10K) SW windward aspects were getting scoured somewhat. Some small fresh wind pockets were noted on lee aspects, but it seemed most of the blowing snow was sublimating and only affecting some minor fresh cornice development.

Winds kept snow surface cool and I suspect south facing will still be soft on Tuesday morning.

200 - 240 cm (~6'-8') HS on NE aspects between 9500' and 10,500'

170 cm HS on SW aspect at 9500'

Red Flags
Red Flags
Recent Avalanches
Poor Snowpack Structure
Red Flags Comments
Recent crowns from 1 - 2 meters still visible and that should make anyone suspicious about stabiity. Poor snow structure with deep slab instabilities.
Avalanche Problem #1
Problem
Persistent Weak Layer
Trend
Decreasing Danger
Problem #1 Comments

Faceted snow now down about 1.5 meters (5') on upper elevation NE aspects and this seems to be the weak layer for much of the natural and intentional avalanche activity over the past cycle. However, boring test scores with ECTX and PST arrest (PST 55/145 Arr). [Boring is ok!] More about this layer in comments.

Snow Profile
Aspect
Northeast
Elevation
9,600'
Slope Angle
34°
Comments

$64,000 question of course is when does the snowpack stabilize from the recent period of heavy snow and water weight over the past 7-10 days? My travels the past few weeks have been primarily in BCC, so was curious how upper LCC was faring. Overall am finding a snowpack in upper LCC that is showing signs of strengthening. Pit profile shows the upper 140 cms right-side up, with somewhat weaker faceted snow and depth hoar in the bottom 80 cms. Looked at lots of old, faceted grains in the bottom 120 cms of the snowpack and they continuing to round and sinter. Some layers appear to be almost all rounds. Even the depth hoar down near the ground is rounding with only a few signs of old striated crystals.

With weak layers now buried over a meter deep, extended column test no longer that useful. Today's results were ECTX.

I did perform a propagation saw test (PST), a more useful test when weak layers are buried > 1 meter. Admittedly not a test I perform very often, but the fracture did not not propagate the length of the column. (PST 55/145 Arr). In reading SWAG guidelines on this, a concern is the fracture occurred after only cutting 1/3 of the column (55 cms on a 145 cm column), but the fracture did not propagate to the end of the column. My interpretation from SWAG is that fracture propagation is unlikely.

Overall am feeling we are moving in the right direction as the snowpack gains strength and adjusts to the recent load and warm temps. The good news is that in upper elevation LCC where there is a deeper snowpack, I would imagine it is getting increasingly difficult to trigger an avalanche, and likely places would be sweet spots such as steep rocky terrain and islands where the snowpack is thinner. The bad news of course is triggering such large slides would likely be unsurvivable.

I'm still going to give steeper slopes more time to adjust, but I did like what I saw today.

Am really interested in what others are finding and thinking about this. Hopefully others will share their thoughts ........

Video

Photo is from crown of recent avalanche just off of Patsy Marley ridgeline. Bruce has already covered this incident well, but the visual really reminds me I have no interest in dealing with hard slab avalanches.

Also finding some additional cornice development along leeward aspects from the SW winds. The cornices are already quite large and overhanging, and fresh drifting today made them even more sensitive.

Video
Today's Observed Danger Rating
Considerable
Tomorrows Estimated Danger Rating
Considerable