A little knowledge about how thunderstorms develop will give a better understanding of why more thunderstorms occur in the warm summer months. The two things needed to cause a thunderstorm are moisture and rapidly rising warm air. The time of the year we are most likely to have those conditions is the spring and summer.
During the spring and summer months, the sun heats the earth’s surface during the day. The heat on the surface of the earth warms the air around it. The warm air, being lighter than cool air, rises in what is called an updraft. As it rises it expands and cools. If the air is moist, then the warm air condenses into a cumulus cloud. This continues as long as the warm air below continues to rise.
Thunderstorms develop more often in areas of high humidity. It is the moisture in the air that rises into the atmosphere in conjunction with warm temperatures where it can cause a thunderstorm to form. Summer air has a greater potential for bringing on a thunderstorm because it is able to hold a lot more water vapor than colder winter air.
The temperature of air is what controls the amount of water vapor it can hold. Since warm air is able to contain much more water vapor than cold air, then the warm summer air is conducive to the development of thunderstorms. As the temperatures rise, the air’s capacity for holding water vapor increases at an increasing rate.
Atmospheric instability is also a condition that favors the formation of thunderstorms. High surface temperatures can favor instability which has a tendency toward vertical upward motion. For this reason, thunderstorms are more numerous in the summer in the middle, warmer latitudes of the earth and during the warmer hours of the day.
Heat, however, is not the only requirement for the development of a thunderstorm. In addition the warm air must be rich in water vapor. The heat of the air causes condensation which, when released into the rising air, creates the principal source of energy for the storm’s development.
Thunderstorms often begin in the morning of a hot day when humidity is high. The sun’s heat causes the upward movement of the moisture and when it reaches the cooler heights, it condenses into clouds. These clouds increase in size until they become saturated with all the water vapor they are capable of holding.
When the clouds can no longer hold up the water vapor, the droplets begin to fall. If there is no instability then a light shower occurs. With atmospheric instability what happens is a thunderstorm. This is more common in the warm summer months. Thunderstorms are more frequently seen in the U S from the lower Midwest to the East and Southeast. These areas have much more humidity than other parts of the United States.