Observation: Willows

Observation Date
1/2/2017
Observer Name
B
Region
Salt Lake » Big Cottonwood Canyon » Willows
Location Name or Route
Willow Heights, West Willow, Mule Hollow
Weather
Sky
Overcast
Precipitation
Moderate Snowfall
Wind Direction
West
Wind Speed
Moderate
Weather Comments
Temperatures remained winter like and cold with daytime highs staying in the upper teens at 9000. Winds were very active in the beginning of the Storm that began in Silverfork at 1900 hours on Sunday evening with very violent and extremely Intense Gusty SW Winds. Grauple composed of at least the first 2 inches. Winds were Strong for at least 2.5 hours, if not longer. Temperatures were in the mid to upper 20’s and the snow was cold and dry. At 0500 on Monday HST appears to be around 5 inches. Throughout the day the PI Rates were averaging S2 with periods of much more Intensity. At 2100 hours HST now at 12 inches. Winds calmed down significantly at mid elevations by mid morning, yet on ridgelines at 9500 feet and above they were in the Low End of the Moderate Category. Wind Blown and or Transport was Moderate.
Snow Characteristics
New Snow Depth
12"
New Snow Density
Low
Snow Surface Conditions
Powder
Wind Crust
Melt-Freeze Crust
Snow Characteristics Comments

In exposed areas with SW-W aspects the Winds had stripped off much of the Storm Snow with the PreStorm M/F Crust either on the surface or just barely buried. As the day proceeded these Crusts and inconsistencies became more covered. Riding got progressively better as the day went on, and by 1400 with at least 9 inches of New Snow it was very good.

Red Flags
Red Flags
Recent Avalanches
Heavy Snowfall
Wind Loading
Cracking
Poor Snowpack Structure
Red Flags Comments
Early time spent near the PC Ridgeline had poor visibitliy and the New Snow was only 5 inches deep. Still Cornices were quite sensitive and easily shearing from approachment. It is a good assumption that by late in the day the combination of more New Snow, the Winds and the Lingering PreStorm Weak Surface Snow were promoting reactive Soft Slabs. Sluffing in the New Snow was observed even by Mid Day. Avalanches as reported by White are indicative of the Poor Snowpack PreStorm Surface Weaknesses and Structure
Avalanche Problem #1
Problem
Wind Drifted Snow
Trend
Same
Problem #1 Comments

Wind Slabs resting on PreStorm Weak Snow appeared to be the main Problem initially today

Avalanche Problem #2
Problem
New Snow
Trend
Increasing Danger
Problem #2 Comments

Soft Storm Slabs resting on the PreStorm Weak Surface Snow will combine to present issues more closely related to Persistent Slab. Up to 10 cm of PreStorm NSF's were observed on the Shady aspects off the West Willow Ridgeline. With the continual Heavy Snowfall that was occurring in the late afternoon until 2100 hours at this writing this problem was obviously seeing an Increasing Trend for Widespread Reactive and Sensitivity.

Danger Rating in the morning hours was Moderate for Wind Slab acitivity as described above. Yet, by late afternoon it appeared to escalate to Considerable. Depending on the extent of the Winds and more Snow overnight it may escalate to High if these factors continue to stay active at the rates observed at 2000 hours.

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