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Weather Conditions That Cause Thunderstorms

Thunderstorms feature lightning and thunder. They often include strong winds and heavy rain, occasionally accompanied by hail. These storms can produce severe weather conditions, including downbursts, tornadoes, damaging hail and flooding. According to USA Today's "Thunderstorm Safety Guide," the U.S. experiences about 100,000 thunderstorms a year, but only 10 percent are severe, with winds of more than 57.5 mph and hail that is dime-sized, or larger. A combination of conditions leads to formation of thunderstorms.

  1. Unstable Air Masses

    • According to the North Dakota Climate Office, unstable air masses can occur when lower air levels are warm and humid while upper air levels are cooler. Since warm air rises, the warmer air from the lower level ascends, cooling and expanding. If enough moisture is present, some of it will condense into a cloud, which will release more heat and cause the air mass to rise more rapidly. Moisture in the lower levels continues to rise upward, ultimately 40,000 to 60,000 feet up.

    Heat

    • Since a heat differential between lower and upper air masses is required for thunderstorm formation, thunderstorms occur more frequently in the afternoon after the sun has warmed the land for a long period. Heat from the earth combines with additional heat generated by cloud formation as warm, moist air rises. According to the National Storms Laboratory, thunderstorms are common over the Florida peninsula because high daytime temperatures combine with moist air from the Gulf of Mexico and the Atlantic Ocean to provide the perfect combination of conditions to produce afternoon thunderstorms. According to the National Lightning Safety Institute, Florida leads the nation in fatal lightning strikes with 126 deaths in a 13-year period.

    Moisture

    • Moisture is necessary in the formation of a thunderstorm to produce clouds. That process generates more heat, causing a violent overturning of warm and cold air masses. As a storm uses up moisture as rainfall, it eventually stabilizes the atmosphere.

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