The Department of Water Resources for the State of California runs the CIMIS website (California Irrigation Management Information System).
They have a series of weather measuring systems scattered throughout the state and from this website you can access the data from these stations. Some information is Max-Min air and soil temps, max-min RH etc. Averages too.
You can get readings by the hour or by the month.
Great info if you're planning to grow your plants outdoors.
Registration is required but it is free.
* Note: edited to include url