Yesterday is what I would call the first day of "fall". AKA when you woke up in the morning it wasn't already obnoxiously hot. That comes about an hour later.
The lows are finally starting to dip below 70, but just barely.
It really depends on you. Me? I went for a run last night and then sat outside for about 5 hours in a t-shirt and shorts. But I know others who would need a jacket.