We are at that time of year when most of our rain comes from something we call convection. Convection means a transfer of heat. A convection oven transfers heat from the coils to the food inside. In weather the heat is transferred from the ground upward to the air. As the heat bumps into layers of cooler air, clouds and localized thunderstorms occur. When a bunch of these localized storms come together in a cluster, they can feed on each other and build severe storms.