A listener asked “Why are we more likely to get frost on a clear night rather than a cloudy night?” One culprit is radiational cooling. Radiational cooling occurs when more heat is lost through outgoing radiation than is gained by absorption of incoming radiation. On a clear night there is little to block this transfer of energy from the surface, through the lower atmosphere, and out to space. When there is significant cloud cover, however, the clouds absorb the out-going radiation, and re-emit a significant portion back to the lower atmosphere. That’s one reason for the description of a “blanket of clouds”.
Mary Knapp, Weather Data Library