It all has to do with relative humidity, which determines how much water the air in a particular environment can hold. Warm air can hold more water than cool air. During the summer in West Virginia, the air is warm and sometimes muggy. When the muggy air enters your crawl space, it mixes with the cooler air below your home (since your crawl space is covered from the sun). Since cold air cannot hold as much water, condensation forms within your crawl space while humidity simultaneously rises.