Usually created by surface heating, convection is upward atmospheric motion that transports whatever is in the air along with it—especially any moisture available in the air. A thunderstorm is the result of convection. What is a severe thunderstorm?
How many thunderstorms are there? Worldwide, there are an estimated 16 million thunderstorms each year, and at any given moment, there are roughly 2, thunderstorms in progress. There are about , thunderstorms each year in the U. When are thunderstorms most likely? Thunderstorms are most likely in the spring and summer months and during the afternoon and evening hours, but they can occur year-round and at all hours.
Along the Gulf Coast and across the southeastern and western states, most thunderstorms occur during the afternoon. Thunderstorms frequently occur in the late afternoon and at night in the Plains states. What kinds of damage can thunderstorms cause?
Many hazardous weather events are associated with thunderstorms. Under the right conditions, rainfall from thunderstorms causes flash flooding, killing more people each year than hurricanes, tornadoes or lightning. Lightning is responsible for many fires around the world each year, and causes fatalities. Hail up to the size of softballs damages cars and windows, and kills livestock caught out in the open.
The cloud starts to look dark and grey as more water is added to it. And the growing droplets that make up the cloud become heavy. Raindrops start to fall through the cloud when the rising air can no longer hold them up. Meanwhile, cool dry air flows downward in the cloud, called a downdraft, pulling water downward as rain. With an updraft, downdraft, and rain, the cloud is now called a cumulonimbus cloud and the cycling of air up and down is called a thunderstorm cell. The moving air within the cloud builds up electric charges as it slides past other air.
The build-up of electric charges allows lightning to form, much in the same way that you can create a spark after shuffling your feet on a carpet. Thunder is the sound that happens when lightning strikes. It often happens after you see the bolt of lightning because sound travels more slowly than light. Another way to classify thunderstorms is by the location where they form and the reason that air rises.
The pictures below describe three different ways that lifting of air can begin: due to a mountain or hillside, within an air mass, or at a storm front. Orographic thunderstorms are caused by air that is forced up by a mountain or hillside.
Air mass thunderstorms are the result of localized convection in an unstable air mass. Frontal thunderstorms occur along boundaries of weather fronts e. Skip to main content. More About Storms.
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