Source: The Castaic, CA weather data displayed above is derived from the NOAA (National Oceanic and Atmospheric). Air quality and pollution data is derived from the EPA (United States Environmental Protection Agency). Air quality and pollution levels measured in a particular area may not be representative of the entire county.
Plant fescues when fall temperature reach about 75 F. The next best time to plant fescue seeds is when rising temperatures in spring reach 60 F. Summer isn't a good time to plant fescue lawns, because fescue grass tends to go dormant during periods of high temperature.
Honestly this grass looks the best in the spring, but if you take care of it you can make it look good most of the year. As it gets hot and humid Blue Fescue can kind of peter out. If it does just trim it back and in a few weeks it will look good again.