The contrast of temperatures across the nation is at its annual minimum. And during the month, temperatures begin to drop slightly especially across the northern states. But the air is still very warm and in most places humid.
Pressure gradients are at their annual minimum and winds as a result also tend to be light.
The jet stream and storm track lift northwards to their most poleward position. The jet on average enters the West Coast near Seattle, WA and tracks across southern Canada to Newfoundland. The storm track shifts north into Canada. Their effect on the states is usually limited to the fronts that they drag across the northern areas. Important large scale, low pressure storm systems are rare across the United States.