32nd Annual Backcountry Benefit- Get Your Ticket Now!
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: Brighton Perimeter

Observation Date
3/23/2017
Observer Name
B
Region
Salt Lake » Big Cottonwood Canyon » Brighton Perimeter
Location Name or Route
Brighton Perphery: Hidden Canyon, 10420, Claytons/Lackawaxan, Brighton Back Bowls, 100 Turn Gully, Figure 8
Weather
Sky
Obscured
Precipitation
Heavy Snowfall
Wind Direction
Northwest
Wind Speed
Moderate
Weather Comments
Skies vacillated betwen Overcast and Obscurred. Due to this, photos were not worth it. Snowfall rates from 0900 until 1400 were sustained in at least the S3 range. Winds were Calm until 1200 hours and then in the afternoon the NW winds were in the low end of the Moderate range; and Wind Blown and or Transport was in the high end of the Light range. Temperatures remained around freezing at 8000 throughout the day and in the mid to upper 20's at higher elevations. Cloud cover remained enough in tact to keep the snow from being adservely affected.
Snow Characteristics
New Snow Depth
12"
New Snow Density
Low
Snow Surface Conditions
Powder
Wind Crust
Melt-Freeze Crust
Snow Characteristics Comments

Storm totals never seemed to be able to get more than 12 inches despite continued snowfall throughout the day. The residual warmth venting out of the snowpack kept grabbing the new snow and assimilating it into the buried wet and damp underlying layers. Wednesdays storm appeared to drop 4 to 5 inches with the upper half of this being graupel. At 0900 there was only 3 inches of light density snow that fell overnight, yet due to the heavy snowfall rates at least another 7 fell during the day. Also in the early morning hours the "scratchy old snow/frozen surface made for slippery riding. Fortunately conditions improved as the day progressed along with accumulating snow.

Soft wind slabs were forming in the upper elevation exposed terrain in the Back Bowls. The slide off of the West face of Milly appeared to have gained cohesiveness due to cross loading. In other areas there were 4 finger plus wind slabs, and associated scouring in the fetch areas.

Red Flags
Red Flags
Recent Avalanches
Heavy Snowfall
Wind Loading
Cracking
Poor Snowpack Structure
Red Flags Comments
Poor snowpack structure that saw activity today was due to the supportable bedsurface from Wednesdays snow and warm temperatures. Slope cuts were easily triggering long running Loose Snow Dry Avalanches in the light density new snow that fell since 2200 on Wedensday. One such long running sluff ran at least 650 vertical on a NE facing gully off of Claytons. The associated weak layer was the previously mentioned graupel, and these graupel pellets were very large and up to 4 mm in size. In many areas the graupel layer was 6 cm deep. As the day progressed the sensitivity of this weakness became less reactive, yet even at 1400 it was still easy to slope cut this weakness on slopes with angles > 35 degrees. In areas receiving even minimal wind transport and loading insignificant cracking was observed, but it would not be unlikely that in the most exposed and loaded terrain in the upper elevations these issues were greater and more problematic.
Avalanche Problem #1
Problem
New Snow
Trend
Decreasing Danger
Problem #1 Comments

See above, unfortunately no photo of the one off of Claytons due to poor visibility. This Slide was approximately 45 feet wide and kept entraining significant amounts of snow upon descent. Regardless, this problem was manageable.

It is likely that this problem will continue decrease in danger trend wise due to the residual warmth of the snowpack and it's associated venting.

There was also several areas where there were small naturals of Loose Dry that appeared to run during the high PI rates.

Avalanche Problem #2
Problem
Wind Drifted Snow
Problem #2 Comments

See above with regard to cross loading potential that may have helped make the slide on the west face of Milly more cohesive. Lingering wind slabs on Friday may still be of concern in the upper elevation exposed and loaded terrain. These slabs may become less sensitive as Fridays temperatures begin to skyrocket.

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