December 30
Porter fork trailhead-main Porter-west Porter-Neffs
Elevations, slope angles and aspects
5000-9700', angles over 35°, north, east and west facing aspects
Snow conditions
2" of new snow beginning the day increased to about 6" in the afternoon.
Most of the snow was light density but, graupel was added during a period of more dynamic snow showers accompanied by wind.
Bonding of new snow to the old surface was poor.
Avalanche activity
Numerous new snow avalanches were encountered, both natural
and human triggered.
Slides were released by kicking small cornices
and with protective ski cutting.
The slides were on east, northeast and (somewhat surprising) west facing aspects. Slope angles were all over 35°.
Slides initiated and running on old bed surfaces from the mid December cycle were lickety splitting down the slope, packing a significant punch.
They ranged in size from 4-10" deep, a few feet to over a hundred feet wide, the largest running several hundred vertical feet.
Weak layer, in most cases, near surface faceting, formed during the extended period of high pressure.
The slides on west facing in upper Neffs were wind drifts on stout melt freeze crusts.
Weather
Snow, heavy at times, moderate temperatures. Winds from the west, both in drainages and on the ridges, were gusting to around 20 mph at times.
Evaluation
The poor bond experienced during the storm should increase with settlement. Faceted old snow surfaces will hamper the bonding.
Would expect continued instability of new snow. Wind drifted slopes, especially those with old bed surfaces, could produce larger, longer running slides.
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