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Observation: Brighton Perimeter

Observation Date
1/10/2017
Observer Name
B
Region
Salt Lake » Big Cottonwood Canyon » Brighton Perimeter
Location Name or Route
Brighton Periphery
Weather
Sky
Overcast
Precipitation
Light Snowfall
Wind Direction
Southwest
Wind Speed
Moderate
Weather Comments
Low Cloud Cover with adequate visibility allowed for decent observations of possible Naturals from the overnight Snowfall and Winds. No Naturals were observed in the Steep N and NE Facing Chutes off of Claytons. Winds appeared to be mostly Light at 0900 hours, yet they continually became more active as the day progressed. Winds were mostly in the Moderate Range out of the WSW, and Wind Blown and or Transport was observed throughout the day. Temperatures remained mild with 9000 foot highs getting close to 30 degrees.
Snow Characteristics
New Snow Depth
9"
New Snow Density
Medium
Snow Surface Conditions
Powder
Dense Loose
Wind Crust
Snow Characteristics Comments

New Snow totals overnight were 5 inches at 8000 feet with possibly a few more inches in upper BCC. Yet, it was hard to tell the true depth due to the Moderate to Strong Winds associated with this latest event. Wind Scouring and Sculpting was obvious with unique Wind Pillows and Rolls well down off the highest ridgelines. Excellent Riding on a creamy dense Powder was found on all but the most exposed West and Southwest areas. Low Angle riding was superb; and some steep lines were ridden safely in the areas that were not Wind Loaded. The initial part of the Storm that began at 1430 on Monday saw at least 2 inches of Graupel fall to start this latest event. The rest of the event had at least 5 more inches of medium density new snow resting on the Graupel base. By 1500 a new part of the latest event became active, and at 2000 hours another 4 inches has fallen. The initial part of this latest short wave came in peacefully, yet by 1800 the WSW Winds have become very active even at 8000 feet.

Red Flags
Red Flags
Recent Avalanches
Heavy Snowfall
Wind Loading
Cracking
Poor Snowpack Structure
Red Flags Comments
In the early morning hours Slope Cuts were easily triggering 4 to 8 inch deep by at least 60 foot wide pockets of Soft Wind Slabs on Steep Slopes and Roll Overs facing N and NE. Cracking was also observed on these same features on slopes with angles > 37 degrees. See 10420 Avalanche Report for Cornice Drop induced Slides. During the day snowfall was averageing S1 rates, yet from 1300 on, the rates have increased and been sustained at at least S2 rates. Wind Loading out of the WSW was very active throughout the day and appears to have increase by mid afternoon. Poor Snowpack Structure continues to be mostly confined to the top 15 inches, and or the new snow since last Saturday.
Avalanche Problem #1
Problem
Wind Drifted Snow
Trend
Increasing Danger
Problem #1 Comments

See above and 10420 Avalanche Observation. And these Winds appear to have a slightly variable component to them vacillating from SSW to WSW. With the forecast for these Winds to be sustained overnight into the Moderate Range, it appears that this problem will be increasing with additional snowfall.

Avalanche Problem #2
Problem
Cornice
Problem #2 Comments

See Avalanche Report; and additional Cornice Building/Falls were resulting in Observed Cornice Failures on many very steep N and NE facing Slopes on the 10420 Ridgeline.

The aforementioned Graupel Layer in the beginning of the latest event appeared to be the Weak Layer in the easily triggered Wind Slabs, and in other steep riding done where Wind Loading was not an issue the moderate temperatures appear to be keeping the transitional Storm Layers mostly unreactive.

Due to these Problems the Danger appeared to be an Isolated Considerable; and this Danger Rating will most likely be increasing to a more Widespread Problem on Wednesday with more Precipitation and Winds.

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