Is it too late to overseed my lawn here in San Mateo, Ca? Our first frost is normally mid December. Our should I do my normal aerate and fertilizer program and wait until spring to overseed?
Grass seeds need soil temperatures in the 45 to 65 degree range to germinate and a bit lower then that to grow. Even if your air temperatures drop below freezing it they do not stay there for quite some time that soil temperatures will not drop that far. Average air temperatures around here are still in the 50's even though we have had some temperatures in the upper 20's and the soil temperatures here are still in the lower 50's.
I would suspect that the soil temperatures in your area of the world do not drop so low as to inhibit seed germination and any grass that you do get started now will have a better chance of surviving summer, then grass started next spring.