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Observation: Snowbird periphery

Observation Date
1/21/2017
Observer Name
B
Region
Salt Lake » Little Cottonwood Canyon » Snowbird periphery
Location Name or Route
Snowbird Periphery
Weather
Sky
Obscured
Precipitation
Heavy Snowfall
Wind Direction
West
Wind Speed
Light
Weather Comments
Heavy Snowfall throughout the early morning hours until 1630. Snowfall Rates averaged S5. Winds were mostly out of the West and at 8500 feet they were in the Light Range. Regardless there was Moderate Wind Blown and or Transport occuring throughout the day. Temperatures remained cool and appeared to be in the mid to lower 20's.
Snow Characteristics
New Snow Depth
2'
New Snow Density
Low
Snow Surface Conditions
Powder
Snow Characteristics Comments

In areas traveled the New Snow was mostly right side up, yet there were two distinct reactive density breaks within the New Snow. One was 15 cm down and the other 45 cm down. By 1530 it began to snow more Mixed Forms with some small graupel, and at 8000 feet in BCC this graupel was beginning to help create a small density inversion in the New Snow. Trail Breaking was difficult in the LCC where the New Snow was at least 60 cm. New Snow at 8000 feet in BCC was 30 cm. Of Note: Low Angle riding in LCC was difficult due to the overall depth of the New Snow. Other parties reported excellent riding conditions ("Best of the Year") from the Meadow Chutes.

Red Flags
Red Flags
Recent Avalanches
Heavy Snowfall
Wind Loading
Cracking
Poor Snowpack Structure
Red Flags Comments
Poor Snowpack Structure confined to the New Snow/Old Snow Interface from the beginning of the Storm Cycle that initiated on Wednesday. NSF's appear to be the Weak Layer of concern, and there were also areas where the Light Density snow that occurred during the initial part of the Storm appears to be reactive where it sits on the Pre Storm 4 cm M/F Crust. This Crust was observed on a West aspect at 8500 feet. Of Note, there was another buried M/F Crust 14 cm down from the previously mentioned M/F Crust, and this Crust was not only thinner (2 cm) it was also capping a buried Grauple layer that was still loose in structure, see photo. Widespread Natural Loose Snow Avalanches were observed in Lower Elevations as well as Mid Elevations, and they appeared to be occurring in the previously cited upper density break weakness at 15 to 20 cm down. Cracking was observed involving both of the sensitive density breaks. Despite no signs of significant Wind Loading in the areas traveled, Remote Weather Sites indicate Likely Problems with the abundant Light Density New Snow available for Transport.
Avalanche Problem #1
Problem
Wind Drifted Snow
Trend
Increasing Danger
Problem #1 Comments

A combination of Storm Slab with the contributing factor of Wind Loading appeared to be the most significant and Dangerous Avalanche Problem on Saturday. And, the weather forecasts appear to indicate Wind Speeds will be sustained at velocities capable of either maintaining this Hazard and or having it Increase overnight and into Sunday.

Avalanche Problem #2
Problem
New Snow
Trend
Same
Problem #2 Comments

The Widespread Natural Activity observed on Saturday may not be as reactive early on Sunday before the next significant impulse arrives later in the day. Regardless as it was on Saturday when all slopes over 40 degrees were exhibiting reactivity, all steep slopes will still be suspect in areas that have received at least 45 cm of New Snow; and with the slight density inversion that is going on this may help keep this problem active.

The Persistent Slab issues related to the buried Pre Storm NSF's may become more of an issue late on Sunday and into Monday as the Water Weight from these series of Storms accumulates.

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