December 21
Bowman trail, Yellow Jacket, Alexander Basin, Millcreek.
Elevations, slope angles and aspects
6400-9200, angles over 35°, all aspects.
Snow conditions
4-12" recent snow, elevation dependent, over a variably crusted base. Recent snow was light density with good settlement.
Crust was stout and supportable at lower elevations, spongy up high.
Weather
Overcast skies with occasional partial clearing. Snow flurries at times, little accumulation. Moderate temperatures and light wind.
Avalanche activity
Slides were found in two drainages, 9k or lower in elevation.
This one, ene facing into Alexander Basin was the result of a cornice fall.
Stress fractures from the other path, trigger unknown, n-ne facing, 40°+, starting zone.
Both slides were new snow only, fracturing within a density change and occasionally stepping down to the old surface as they ran.
Both left large patches of un-slid snow, lower angled or slightly stronger, less sensitive layering.
Neither broke into the older snow.
Weak layer was no longer sensitive.
Evaluation
Density changes within new snow, probably coupled with a period of stronger wind, produced an avalanche cycle, first noted yesterday.
Weather guessers have called off the increasing rain-snow line but, still have increased densities in the latest round.
Would expect increased instability.
Deeper larger slides into older layering possible but not probable because of the high density cap under recent storm snow.
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