I live here...
The past few days, it HAS been much cooler than normal for this time of year.
Yesterday's high was 75. Today's high is supposed to be 76.
The mornings, up until about 10am have been overcast and chilly. The temperature in the EARLY mornings is CHILLY (for us So. Cal people). I wore jeans and a light sweater this morning to take my son to school. At 10am, the temperature was still only 67 degrees, although the sun was starting to come out.
Yesterday, my son and I went to
Disneyland in the early morning. I was wearing a t-shirt and capri pants. I was FREEZING! I wish I had worn a sweater...I did not start feeling warm until close to 10:45am.
Similarly, once the sun sets, it gets VERY cool (low 60's). If you are planning late nights, you will need something.
Maybe not a SWEATshirt, but at least a lightweight hoodie or similar, or some thin long sleeved shirts to wear over t-shirts (think: layers that can be removed and stashed in a backpack, that AREN'T bulky).