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

mid-ridge

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.

middle-bowl

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.

lower-roll

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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