Thunderstorms can happen at any time of the year at any time of the day but usually they occur during a particular season and generally later in the day. At any given moment, there are around 2,000 thunderstorms of varying severity in progress around the world with approximately 100,000 each year in the United States.
These storms are categorised into five levels based on the risk they pose to life and the damage they can cause - from Level 1, minor storms which cause minimal or no damage, to Level 5, the highest rating for the most violent electric storms. According to the National Weather Service (NWS), a severe thunderstorm is defined as one which: produces a tornado, winds of at least 58 mph (50 knots or ~93 km/h), and/or hail at least 1″ in diameter. Only thunderstorm warnings about Level 3 are issued.
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Thunderstorms are seasonal and are most likely in the spring and summer months with the majority taking place between April and August. In the US, the southeastern states suffer the most electrical storms - according to the National Weather Service, during the last 30 years, Florida has been the hardest hit with thunderstorms occurring on 80 to 105 days of the year. The reason for that is the abundance of warm, moist air from the Gulf of Mexico and Atlantic Ocean - key ingredients in the development of electric storms which produce thunder and lightning.
Mammatus clouds seen from NWS Omaha/Valley. The thunderstorm was in Burt County and this is underneath the anvil cloud that extended well to the south. pic.twitter.com/x94MthBq31
— NWS Omaha (@NWSOmaha) August 19, 2022
Thunderstorm development
More often than not, thunderstorms strike late in the evening, at night or during the early hours of the morning. It is during the evening when the earth’s surface is at its hottest after hours of direct exposure to the sun’s rays. By the early evening, the warm ground begins radiating energy, producing hot air which expands and rises upwards into the atmosphere. When that hot air comes into contact with cooler air at high altitudes (typically above 10,000 metres/33,000 feet), it cools, creating water vapor and a cycle begins. The cooled air then descends, warms and rises again, eventually forming clouds. When this process happens on a large scale over several hours, large thunderclouds start to form. As the water droplets increase and grow larger, the cloud will turn grey. The cycle of air rising and sinking forms a thunderstorm cell.
Another spectacular shelf cloud moved over @NASAStennis and the @NWS National Data Buoy Center complex this morning! @NWSSPC #shelfcloud pic.twitter.com/DVO4VWPH3g
— NWS_DataBuoyCenter (@databuoycenter) August 19, 2022
When the thundercloud moves to higher altitudes where temperatures are lower, the water droplets are converted into small ice particles which, when they bump into each other, create static electricity. When that happens on a large scale, those electric charges will eventually cause flashes of lighting and loud cracks of thunder, the telltale signs of that a thunderstorm is on the way.
Thunder is created when lightning passes through the air. Immediately after the flash, the air cools and quickly contracts. This rapid expansion and contraction creates a sound wave - a loud boom or cracking sound. The sound of thunder takes around five seconds to travel one mile, so you can calculate how far away the thunderstorm is by counting the number of seconds between the flash of lightning and the sound of thunder, then divide that number by five.
