When cool dry air aloft moves in over warm, humid air, thunderclouds build due to convection .
Convection is the transfer of heat through groups of molecules.
In order for convection to occur you need free moving molecules, such as water or air. Make it happen 1. Let the water sit for 30 seconds until completely still. Place a blue ice cube at one end of the plastic container. Add two drops of red food coloring to the water at the opposite end of the plastic container.