We toured up to and observed this avalanche today . We believe it occurred on 11/27. It appeared to be a D1.5-2 wind slab that stepped down into the persistent slab.
Observation: Hatcher Pass
Location: Japanese Trees
Started up common uptrack for Japanese Trees at 10:45 am and ascended to the bench at ~2400 ft. We decided to stick to soft snow lower down and found good turns on several laps towards the top of Skeetawk. Returned to car at 2:50 pm.
Forecaster Comments
Avalanche Details
Observed an avalanche from 11/27 with avalanche debris on north facing aspects of Frostbite from a distance. We suspect that this slope was wind loaded during the last wind event based on the extensive scour on adjoining south aspects and presence of cornices along the ridgeline. Avalanche width is approximate and crown depth appeared to be 12"+ from a distance.
Weather
Partly cloudy skies in the morning transitioning to cloudy in the afternoon. Temperatures were upper teens to low 20s with calm winds building to gentle southern winds in the afternoon.
Snow surface
~6-12" of settled snow is present on east facing aspects between 1200-1400', locally wind slabs (10s feet in width) and ice scour are present between 1200-1400'. Wind scour and development of wind slabs appeared to be more widespread above 2400'.
Snowpack
No formal tests were conducted. Hand pits suggest that the 6-12" to settled snow overlies a ~1" thick rain crust between 1200-1400' and appeared to be bonding well. Hand pits failed under moderate effort on poorly-formed facets ~1-2mm in size below the rain crust. Height of snow between 1200-2400' was found to average 50-100 cm. At 2400' wind transport and deposit of snow on snow on north faces was widespread with snow locally >1 m in depth. Above 2400' wind slabs ~12" down were found to break within wind transported snow; however, ski cuts of localized wind slabs/cornices did not produce failure.
Hand pit at ~1900' showing failure below rain crust.
Hand pit at ~2400' showing planar failure ~12" down on wind slab.
Ski cut of wind slab.
Avalanche paths observed on north aspects of Frostbite.
View of valley