And again, fluids of slightly different densities do not mix well. This tendency not to mix accounts for one of the most familiar types of weather systems. When that warm air reaches the condensation level, you get a solid cloud mass and rainy weather. Jeffrey S. Peake is an assistant professor of geography at the University of Nebraska at Omaha. Also, on a summer day, when clouds result from convectional heating from below, the formation of one cloud and the resultant release of latent heat tend to lower the pressure of the air immediately around the cloud and encourages additional air to rise upward, expanding the cloud in one part of the sky.
Most fogs tend to be found under conditions of light wind.