Ad
The National Forest Service Logo
icon-add Observation
Forecasts
Logan Ogden Salt Lake Provo Uintas Skyline Moab Abajos Weather Archives How to read the forecast
Observations & Avalanches
Submit Observation Observations Explorer All Observations Avalanches Fatalities Weather Place Names Map Archives
Education
Avalanche Class List UAC Class List Online Classes Resources and Tutorials Avalanche Awareness Develop Skills
Events
Store
About
Contact Who we are Core Values Staff Board of Directors Past Forecasters Sponsors Annual Reports Sign In
Blog
icon-add Observation
Donate / Join

Observation Date
1/3/2017
Observer Name
Greg Gagne with Bob Frey
Region
Salt Lake » Little Cottonwood Canyon » Davenport Hill
Location Name or Route
Davenport Hill
Weather
Sky
Overcast
Wind Direction
Southwest
Wind Speed
Moderate
Weather Comments
Winds increased throughout the morning, blowing steadily along the ridges, and drifting well down off the ridges into the mid elevations.
Snow Characteristics
New Snow Depth
20"
New Snow Density
Low
Snow Surface Conditions
Powder
Wind Crust
Snow Characteristics Comments

It seemed from all my samples, there is 50 cm (20") of settled snow from the recent storm. Right-side up with very low-density snow. However, once the wind went to work and began to drift the snow, dense wind slabs began to form, particularly along upper elevation ridgelines.

Saw quite a bit of evidence of sluffing within storm snow, so am guessing upper LCC went through a natural cycle during the storm on Monday or overnight into Tuesday morning,

Red Flags
Red Flags
Recent Avalanches
Heavy Snowfall
Wind Loading
Red Flags Comments
The new snow was fairly well behaved and I could only get sluffing in the surface. As the winds began to drift snow onto a variety of aspects (although primarily northerly) the fresh wind drifts were sensitive and would easily crack out from your skis.
Avalanche Problem #1
Problem
Wind Drifted Snow
Trend
Increasing Danger
Problem #1 Comments

With so much low density snow to blow around, wind slabs were forming quickly and were sensitive. These are sitting on top of low density storm snow which easily provides a weak layer.

Avalanche Problem #2
Problem
New Snow
Trend
Increasing Danger
Problem #2 Comments

Although there was evidence of some natural activity during the storm, the 50 cms (20") of storm snow was manageable and at best I could only produce sluffing in the top 5-10 cms (2-4") of snow. It appears the storm snow was still not acting as a cohesive slab. Dug quite a few quick pits looking at the old snow interface. There is a widespread, preserved layer of near-surface facets that is ~5cms thick (even thicker in some areas) that formed during the clear weather from Thursday through this past Sunday. Monday's No-Name slide likely failed on this layer. On slopes approaching 35 degrees or steeper I was unable to isolate a column (STC) or STV/STE (very easy or easy) clean shears. I think this preserved layer of NSF will be a player in this upcoming expected stormy period.

Comments

For this upcoming storm, I am primarily concerned about the following existing layers:

1. The layer of near-surface facets now down 45-75 cms (18-30") underneath the Monday/Tuesday am storm snow. On Monday there simply wasn't enough of a slab to make this layer reactive. Was expecting it to be more reactive on Tuesday given all the new snow, but the storm snow was still not acting as a cohesive slab. However, have been getting easy, clean shears on this layer and the grains are quite weak. I am expecting this layer to be reactive with additional dense storm snow.

2. The Monday/Tuesday am storm snow is very low density and will not support the weight of the 2-3" of water and strong winds.

Sustained southwest winds along the ridges were creating sensitive, fresh wind drifts by mid-day Tuesday.

Outside of wind-affected terrain, the hazard appeared Moderate to me as I could only get sluffing within the storm snow. On steeper slopes with fresh wind drifts, I could easily see a Considerable hazard. Hazard at least Considerable by Wednesday morning, possibly quickly rising to High as dense storm snow accumulates.

If this storm comes in as advertised, I would expect the avalanche hazard to rise quickly during the day on Wednesday. Backcountry travelers really need to pay attention to changing, dangerous avalanche conditions with this next storm.

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