Weather that night
I am a retired fixed wing ATP and live in San Diego County, not far from the crash site. The weather that night was not good, low clouds, mountain obscuration with snow and sleet. There were also several heavy cells embedded along with scattered TS. San Diego earlier in the day had a tornado warning, which is almost unheard of here. The nearest weather reporting station is Mount Laguna approx 5 miles north east of the crash site at 5,500ft. The report that evening around the time of the accident was:-
Feb 6, 10:52 pm Temp 30F Dew Point 30F Humidity 100 Wind Chill 23F SW @ 7 G18