Roughly like this
<55F put a long sleeve Gabba over my jersey (or, if <60F and windy/cloudy)
<45F put on tights over the cycling shorts
<40F put on warmer gloves, add thin rain shell over the Gabba

and if it is raining hard, add a thin rain jacket and switch to neoprene gloves. My usual weekend road bike has Crud RoadRacer fenders.