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Observation: Preston Peak

Observation Date
12/3/2017
Observer Name
Gagne/Johnston
Region
Salt Lake » Big Cottonwood Canyon » Brighton Perimeter » Preston Peak
Location Name or Route
Pioneer Peak
Weather
Sky
Obscured
Precipitation
Moderate Snowfall
Wind Direction
Northwest
Wind Speed
Strong
Weather Comments
Arrived mid afternoon just at frontal passage. Sustained winds with strong gusts working around terrain features. Some graupel mixed in.
Snow Characteristics
New Snow Depth
2"
New Snow Density
Medium
Snow Surface Conditions
Powder
Wind Crust
Melt-Freeze Crust
Rain-Rime Crust
Snow Characteristics Comments
Left at 5 pm, and am being generous with the 2" (but hey, 2" is a pretty big deal this season!). Winds were creating small pockets of fresh drifts, but they were < 10 cms (4"). Difficult to determine bonding of new snow with so little new snow, but widespread crust on the existing snow surface was frozen , and storm precip came in cold. From what I was seeing, poor bond. The few mm's of faceted snow sitting on top of the crust had blown away with the pre-frontal winds. Was not seeing evidence of a possible dust layer.
Red Flags
Red Flags
Poor Snowpack Structure
Red Flags Comments
Was first tour of the season for my partner Mark Johnston: When he dug a pit on north aspect below Pioneer Ridge, all he could say when seeing the incredibly weak snow was "wow". Enough said.
Avalanche Problem #1
Problem
Persistent Weak Layer
Trend
Increasing Danger
Problem #1 Comments
Like what others have noted, weakest snow seems to be just below Thanksgiving crusts. (Although not to imply there is *any* strong snow to be found below this crust; this just seems to be the weakest of the weak.) Assuming we add more of a load on top, will call the trend increasing.
Avalanche Problem #2
Problem
Wind Drifted Snow
Problem #2 Comments
The few small pockets of wind drifts we found today may be more widespread by Monday with additional snow and wind. Any drifts will be bonded poorly to the old snow surface.
Comments
Hazard Monday seems to be entirely dependent upon new snow and/or wind. Biggest question is how much of a load can the Thanksgiving crust support? What I was seeing in Brighton backcountry both Saturday and Sunday is widespread crust on all aspects to 10,300'. This crust varies in thickness, so some slopes may support greater loads, while others may fail more easily, especially those that are wind-loaded. Overall I am feeling this crust may be able to support some loading before it fails, and not sure if forecasted water amounts (< 1") are enough to tip the scales widespread. Wind loaded slopes may be a different story.
Just a video of the wind blowing - it sure felt wonderful to be in the mountains with active weather!
Video
Today's Observed Danger Rating
Low
Tomorrows Estimated Danger Rating
Moderate