Radiational cooling is when Heat rises into the atmosphere when skies are clear and the cold settles in at the surface. But when clouds move in during the day it traps the heat at the surface and prevents the heat from dispersing and the cold from settling in at the surface.
So temps will begin to moderate during the next few days until the cool air is cut off completely. We can expect cool temps between upper 50s to lower 60s interior to lower and upper 60s close to the coast this evening. You can also expect some fast moving isolated showers off the Atlantic as well.