The bottom line here is a simple concept on the surface, that becomes extremely complex in short order.
First think of a real, physical greenhouse. Inside it is moist and warmer when it is cold outside, and somewhat cooler when it is hot outside. It is “moderate” because of the humidity in the air.
Now think of the opposite of a greenhouse, the surface of the Moon. If it is daytime, everything is directly hot. But at night, everything is extremely cold. There is no moderation, no moist air, nothing to block the sunlight nor prevent the radiation of heat back into space.
Now think of Earth’s atmosphere. When there are lots of high clouds, radiation from the Sun gets through but is trapped in the atmosphere, and doesn’t radiate back into space as much. When there are low clouds, more radiation is reflected back into space, so the ground is cooler.
However, when there is little moisture in the air at all, visible or invisible, the ground is more like the Moon, getting hot during the day, but cooling off a lot at night.
This can be very noticeable in the desert, dry air with hot days and cold nights.
There is one more twist to things, that the air over the North Pole seems to be shifting back and forth over the high latitudes, like a beanie on a bald head. When the jet stream goes South into the US, cold air from the Arctic rushes down. But then the jet stream pushes back North on our side of the planet, and rides down on the other side, making things cold in Europe and Russia.
And this is kind of unusual as well, but it is a lot more noticeable when there is little moisture in the air. This is why we had a hard winter and a very long spring.
The big question is why is there less moisture in the atmosphere right now?
The absence of clouds means that the weather 30 to 40 miles from the Gulf is not being influenced by Gulf moisture.
If we have a southerly wind, we tend to have clouds, though they may not be rain producers...
If we have a northerly wind, it usually is a cloudless day as the moisture tends to come from the Rockies and deserts (plains).
I don't have an answer to the question of why less moisture right now, but the Pacific Ocean is a major influence on the West and Midwest in terms of moisture...
Joe Bastardi says it is because global cooling is worse then we thought. We have atmospheric temperatures dropping and less moisture. So the global oceans are also cooling. Colder oceans means less moisture (less evaporation).