Convection is the organized motion or movement of large groups of molecules based on their relative densities or temperatures. For example, convection is the upward motion of a warm fluid spreading through a cooler one. Weather is the state of the atmosphere and conditions such as dry or wet, cold or hot, stormy or calm, cloudy or clear. In plain terms, we can say that weather happens when wet air goes up in the atmosphere. One cause of rising air in our atmosphere is from the process called convection.
Warm air rises above cold air by convection.
Clouds form when water vapor condenses and molecules cling to each other. While convection is happening and warm moist air is going upwards, there is also the sinking of denser and cooler molecules from the sky moving downward. Convection happens because warm air is less dense than the cold air around it, so it is lighter and rises or goes up in the atmosphere. Evidence of convection happening is seen with the formation and growth of cumulus clouds. We see evidence of sinking motions of heavier and cooler air falling to the earth when the sky is clear or without clouds.