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Observation: Alta Periphery

Observation Date
2/25/2018
Observer Name
B
Region
Salt Lake » Little Cottonwood Canyon » Alta Periphery
Location Name or Route
Alta Perimeter
Weather
Sky
Broken
Wind Direction
Northwest
Wind Speed
Moderate
Weather Comments
Early morning mostly cloudy skies gave way to clear skies for a brief period. By sunset the cloud cover rolled back in. Temperatures appeared to never even get into the low teens at upper elevations. Winds were gusty and even getting into the mid elevations in the early morning hours. By mid day the winds were predominently only observable on the upper ridgelines. Wind blown and or transport was moderate out of the WNW on the exposed ridgelines.
Snow Characteristics
New Snow Depth
9"
New Snow Density
Low
Snow Surface Conditions
Powder
Dense Loose
Wind Crust
Snow Characteristics Comments

Winds from overnight created pockets of soft wind slabs of up 12 inches deep, and were observed on the surface in many locations. Buried hard wind slabs appeared to be more widespread and observed on multiple aspects in the upper elevations. The snow from overnight was low density and in more protected terrain, excellent riding and turning conditions were enjoyed on all aspects. Easterly aspects held the best riding in the upper elevations. Even though the sun came out for the majority of the mid afternoon hours, the cold temperatures appeared to negate the potential for the solar gain to dampen the snow surface.

Wind damage was observed on many exposed ridgelines and on SW, W and NW aspects.

Red Flags
Red Flags
Recent Avalanches
Wind Loading
Cracking
Poor Snowpack Structure
Red Flags Comments
Poor snowpack structure continues to haunt much of the upper elevation off aspect facing terrain. Facet crust sandwiches have yielded various slides into the mid pack layers over the past 10 days, yet a real load has not truly tested these weak layers. Cracking was widespread and observed in the previously cited soft wind slabs. Of note: simple probing and hasty pits by multiple observers continue to note poor snowpack structure in the form of "strong over weak" as identified in the inverted storm layer event that was laid down a week ago, and observed on the 19th. The extreme cold temperatures during this past week appear to have help keep this layer from asssimilating/settling into it's surrounding layers. If this structure continues to be evident, further examining of the grain structure of the culprit layer may indicate small facet growth has been initiated. And at this point, this layer is now buried up to (at the very least) 2 feet below the snow surface in many locations.
Avalanche Problem #1
Problem
Wind Drifted Snow
Trend
Increasing Danger
Problem #1 Comments

Numerous small pockets of wind slabs were observed throughout the Alta Perimeter. Rocky Points, Test Bowl, and Little Superior all had such releases; and these all appeared to unintentionally triggered. With the winds forecast to ramp up overnight this problem may increase into the morning hours on Monday in the exposed terrain.

Avalanche Problem #2
Problem
Persistent Weak Layer
Trend
Same
Problem #2 Comments

See above with regard to facet crust sandwich concerns, and along with this potential problem there are obviously outlying areas with thin snowpack and faceted layer issues that continue to linger waiting for a substantial load to become more widespread and reactive.

Besides the previously cited pockets of wind slab, the tracks observed and ridden on many steep slopes appeared to indicate there was not a widespread avalanche problem today. Without the presence of any natural activity, it appeared that the danger rating was moderate on Sunday; and with the winds increasing overnight and into Monday the danger most likely will escalate to considerable for wind slabs and potential persistent slabs overburdened by wind loading.

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