There is a song that states "It never rains in Southern California". Daytime wise, San Fran will be warm and sunny but not baking hot. LA will be warmer still (like a UK summers day). Vegas is always hot - even into the night. After about 1AM the temp drops quickly, but by the time you wake up after a night out in Vegas, it's warm again - trust me!
The only temp figures I have are for LA, where the day temps will be about 23c and the night time minimum will be 10c. It was 10c today in parts if the UK!