Cloudy versus clear nights

Low temperatures Tuesday morning were a little more mild than what they were Monday morning all thanks to cloud cover and a brisk southerly wind. 

During the day the sun emits shortwave radiation to the earth.  This is what helps heat up the atmosphere during the afternoon.  At night, the earth re-emits the shortwave radiation back to space as longwave radiation.  When clouds are present it can interfere with both the shortwave and longwave radiation from the sun and earth.  On cloudy afternoons, the surface of the earth isn't able to heat up as efficiently as it would otherwise be able to on sunny days because the clouds block the shortwave radiation (or the majority of it) from reaching the surface.  At night, the opposite occurs.   On clear nights all the energy from the sun that had built up during the afternoon is emitted back out to space thus cooling the surface of the earth.  Often meteorologists refer to this as radiational cooling.  When clouds are around at night the heat (or energy) isn't allowed back out to space keeping the surface of the earth warmer.  Think of it as a blanket.  Clouds act like a blanket at night to keep us warm.

Now there are other factors that can contribute to this such as wind direction.  Along with the cloud cover we had a steady breeze from the south which also helped lows overnight from dropping into the 30s.