During the day the cloud cover blocks the sunlight which helps keeps us a bit cooler but during the night it does the opposite. The clouds act like a blanket and traps the heat down to the earths surface. That will be the case Wednesday night
Tonight: Tonight will still be quite cold. The low temperatures will fall into the upper teens to the lower 20s. That is because the winds our coming out of the northwest. We are tapping into a colder and drier air mass. But, the cloud cover will keep us a bit warmer than Tuesday night. Tuesday night the low temperatures fell all the way into the lower teens. A few cities and towns set new record low temperatures. The partly to mostly cloudy sky Wednesday night will trap the heat to the surface and not allow us to cool as fast or as low as we normally would.
The earth hits peak radiation cooling during a clear sky and dry night. The drier the air mass the lower the humidity. Low humidity areas like desserts and high elevation can generate a large temperatures drop. The lack of clouds allows the earth to radiate its heat freely and quickly. Having clouds overhead will trap some of the radiated heat back down to the earth’s surface and not allowing it to escape into space. This is the same reason why we use blankets to keep us warm. The thicker the blanket the warmer you will be.