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Observation: Brighton Perimeter

Observation Date
1/4/2017
Observer Name
B
Region
Salt Lake » Big Cottonwood Canyon » Brighton Perimeter
Location Name or Route
Brighton Perimeter
Weather
Sky
Obscured
Precipitation
Heavy Snowfall
Wind Direction
West
Wind Speed
Moderate
Weather Comments
Mild Temperatures throughout the day with periods of Heavy Snowfall. Winds were at the High End of the Moderate Range at and above 9000 feet. Gusts ventured into the Strong Range. Transport was Moderate.
Snow Characteristics
New Snow Depth
10"
New Snow Density
High
Snow Surface Conditions
Dense Loose
Wind Crust
Snow Characteristics Comments

Warm Temperatures combined with the aforementioned Winds helped lay down a thick blanket of Dense Spring Type Powder. Rimed Stellars and Graupel made up the New Snow Precipitation Particles. Most places had at least 8 inches of this Dense New Snow overlying Tuesdays extremely Light Density Event. The New Snow was inverted in it's overall structure of the top 12 to 20 inches. Despite this the New Snow was dense enough to be mostly supportable, and even though it rode slow, it allowed for decent turning on slope angles between 25 and 30 degrees. Wind scouring was observed on Windward aspects from 9000 feet and above.

Red Flags
Red Flags
Recent Avalanches
Heavy Snowfall
Wind Loading
Cracking
Poor Snowpack Structure
Red Flags Comments
The previously mentioned Inverted Upper Layers speak to at least one aspect of the Poor Snowpack Structure that can be found out there. Despite not observing Naturals digging down into the PreStorm Facets that were buried on Monday/Tuesday, it is Very Likely that this Problem is not only possible but becoming Widespread in Upper Elevation Steep Wind Loaded Terrain on N through E aspects. And Mid Slope Convexities may be even more suspect. SWE appears to have hit 1.5 inches in favored locations that received at least 10 inches; and at 2200 it is still snowiing at an S2 Rate at 8000 feet. Some cracking was observed in the New Snow on slopes with angles exceeding 37 degrees. During the highest PI Rates and Winds in the afternoon Slope Cuts were reported to help initiate Storm Snow Slabs of up to 12 inches deep.
Avalanche Problem #1
Problem
Wind Drifted Snow
Trend
Increasing Danger
Problem #1 Comments

See above, and as these PI Rates and Winds continue overnight this the trend for this Problem will Increase. Forecast is for the Winds to die down by morning, but as of 0500 on the 5th this has not verified in the Upper Elevations. As a result, this Problem appears to have escalated even more overnight.

Avalanche Problem #2
Problem
New Snow
Problem #2 Comments

As this new Load is resting on significant amounts of Light Density Snow, the Storm Slab Potential may Linger longer than the Wind Slab issues.

And, it will be interesting to see how the buried previously cited PreStorm NSF's that were present before the first Event earlier in the week will react over the next 72 hours or more. Forecast of Rapid Warming by Sunday may help activate these potential Persistent Weak Layers to new heights.

Danger today due to the Heavy Snow from today and Winds appeared to be Considerable. With the previously cited Strong Winds at the Upper Elevations, the Danger for Thursday may reach High. Of Note, the Winds have died down significantly at Mid Elevations overnight, and this combined with dropping Temperatures may have helped reduce the Danger at Mid Elevations to Moderate. At the very least the riding in the Mid to Lower Elevations should be much improved with the last layers of Light Density Snow that fell at the end of this latest event.

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