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Observation: Brighton Perimeter

Observation Date
4/8/2017
Observer Name
Evelyn
Region
Salt Lake » Big Cottonwood Canyon » Brighton Perimeter
Location Name or Route
Brighton Perimeter
Weather
Sky
Overcast
Precipitation
Light Snowfall
Wind Direction
South
Wind Speed
Light
Weather Comments
Intermittent graupel squalls, punctuated with breaks and occassional short periods of sun. Winds were almost calm off the ridge lines, but strong enough to drift snow across ridges. Rain/snow line at 6,600' (around the S Curve) on the way up canyon, and had risen to 7,400' on the way down (about Spruces).
Snow Characteristics
New Snow Depth
3"
New Snow Density
High
Snow Surface Conditions
Powder
Snow Characteristics Comments

Snow squalls adding up - nice dense track filling graupel. Best turns on low angle slopes, and it's making a nice dense base for the forecast snow. Should be excellent turning and riding conditions tomorrow out of the winds affected terrain.

Graupel was definitely rolling down off the steeper slopes/rock bands, with graupel pooling 1 foot deep to even 2 feet deep in isolated places below. I observed no real slabs in the graupel pooling, it was just all loose snow for the moment.

Avalanche Problem #1
Problem
Wind Drifted Snow
Problem #1 Comments

With the current snow and wind forecast, I'd expect wind slabs to be the number one issue tomorrow. With winds tapering through the night, it might be a little tricky with some of the wind slabs hidden by soft, end of storm snow.

Avalanche Problem #2
Problem
New Snow
Problem #2 Comments

Again, looking at the forecast, I'd expect storm snow sluffs and slabs on steep slopes, with today's graupel as the weak layer. Would also be alert for and avoid graupel pooling below steep gullies and cliffs. New snow instabilities often stabilize in 24 to 48 hours.

Comments

Upper photo from a northwest facing slope, 9800'. Weakest layer is the graupel about an inch above the old surface crust. I'm guessing the first snow came in so warm and wet, it literally froze onto the crust, at least below about 10,000'. There is also weak snow below the crust, though ECT's had no results on this layer or the graupel. I saw no signs of the near surface facets that were around on Thursday (see Greg's observation HERE) Hopefully they were all destroyed by Friday's strong winds and warmth.

Below around 9,000', even the short periods of sun seemed to be warming the snow, and I'd expect the graupel layer to be much less sensitive.

Second photo is of of a different northerly facing spot - thinner crust, graupel still the weak layer.

Will the crust be a player other than acting as a bed surface? (in other words, could a slide break out below the crust, deeper and wider?) I'm unsure, but expect it would be isolated to upper elevation, NW, N and NE facing slopes, as the crust thickens and strengthens significantly as you drop in elevation or get onto the sunny slopes. Tomorrow, I would dig down to and below that crust if you're planning on getting onto steep, upper elevation northerly facing slopes, checking out the weaknesses above and below the crust.

Winds were almost calm off the ridge lines, but this spot shows there was enough snow to start drifting today where winds were funneled and stronger along the ridge lines.

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