I grew up in the LA area (San Fernando Valley), so I know where you are. A bit risky with the off shore winds, especially if no one knows you are out there.
Last Friday I sailed alone in 15 to 25 mph side shore winds, 50 degree air and 48 degree water. However, if I had a breakdown, I would drift to shore in about 30 mins, with a 30 minute walk back to the car. Not much risk. I have a great 5mm wet suit, booties, gloves and hood, so I am very comfortable sailing in 40 degree F water and air.
My bottom line for sailing comfort is sunny in the 40's or overcast in the 50's (air temp). Water temp doesn't matter much, but it almost ever gets into the 30's in Dallas. I could go a bit lower, but I would probably find myself alone too often.