December 30-31
Bowman, Yellow Jacket, Alexander Basin, Millcreek
Elevations, slope angles and aspects
6400-9700', angles over 35°, north facing aspects.
Snow conditions
Storm total of around 16", settled.
Light density under high density under 6-8" of fluff produced isolated collapsing in the flats.
Wind drifting on east facing aspects initiated cornice falls, resulting in a large slide. Cornice kicking produced only sluffing.
Weather
Overcast skies, cool-cold temperatures, light wind with snow flurries. Little accumulation.
Avalanche Activity
Returned to Alexander on December 31 for a better look at the middle bowl
Found a large avalanche(too cold for good pics).
It probably ran during the windy period following cold front passage, late afternoon on December 29.
The photo is of the right side of middle bowl, showing drifted in portions of the crown, recent sluffing and a large debris pile.
The slide was at least 600' wide including the east chute and all of the middle bowl, north-east-southeast facing. It may be larger because view into upper Alexander was obscured.
It ran about 1500' vertical with cornice falls observed yesterday the likely trigger.
The slide went over both of the breakovers, releasing additional pockets. The lower breakover, pictured in the photo, has a crown of 30+ inches and stepped down into older snow.
Impressive!
Evaluation
Sluffing of light density snow in sheltered areas.
Wind drifting may be an issue on lee slopes, especially at upper elevations.
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