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How Do Thunderstorms Form?
March 1, 2023 at 11:42 PM EST
By WeatherBug's Ali Husain
Thunderstorms are a broad term for rain showers that bring audible thunder, meaning that all thunderstorms have lightning. But how do these storms form?
Three ingredients are required for thunderstorms to form: moisture, unstable air and some lifting mechanism to force the unstable air upwards.
When the sun heats the surface of the Earth, it also warms the air right above it. At rest, the warm air will stay near the surface, but once a lifting mechanism forces it upwards the lifted air will continue to rise so long as it remains lighter and warmer than the air around it (i.e., the air is unstable). There are several mechanisms that can lift air, but some of the most common mechanisms are frontal (cold fronts usually bring the strongest thunderstorms), orographic (mountains, hills and other high-elevation terrain), and convergence boundaries (air collides and has nowhere to go but up).
This transfer of heat from the warm, rising air to the atmosphere (the process known as convection) also brings moisture to upper levels of the troposphere, the layer of the atmosphere where we reside and the weather we know takes place. Here, where the air is cold, the water vapor condenses on particles to form clouds. As the cloud expands, it grows upwards into areas of the atmosphere where temperatures are below freezing.
In the sub-freezing air, liquid water drops begin to cool below the freezing point. Some drops freeze, while some drops become “supercooled,” whereby liquid water remains in the liquid phase despite temperatures being below 32F/0C. The ice particles grow by condensing vapor upon their surface, or by accumulating the supercooled water droplets, which fully freeze upon contact with the ice particles.
The formation of these ice particles is very important for the development of the “thunder” part of these storms. When two ice particles collide in the frozen region of the cloud, the collisions rip off little bits of the particles and an associated electric charge. On a large scale, these collisions end up creating regions of clouds that are positively charged, and some regions that are negatively charged. Wanting to be in a neutral state, the cloud discharges the electricity, creating the brilliant flash of light we call lightning.
This describes the development phase of thunderstorms. The other two phases are the mature stage, where rain begins to fall, and the dissipation stage, where the warm, moist air gets cut off from the storm and rainfall begins to slow, although lightning remains a threat.
Thunderstorms become severe when it has either hail of one inch or greater, wind gusts of 58 miles per hour or more or has produced a tornado. Severe thunderstorms are most common in a swath from Texas to southern Minnesota, but no place in the U.S. is entirely safe from severe thunderstorms. When a severe thunderstorm is forecast for your area, heed any and all official warnings and stay away from flooded roadways. Remember, “Turn Around, Don’t Drown” and “When Thunder Roars, Go Indoors!”
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Story Image via Pixabay
Three ingredients are required for thunderstorms to form: moisture, unstable air and some lifting mechanism to force the unstable air upwards.
When the sun heats the surface of the Earth, it also warms the air right above it. At rest, the warm air will stay near the surface, but once a lifting mechanism forces it upwards the lifted air will continue to rise so long as it remains lighter and warmer than the air around it (i.e., the air is unstable). There are several mechanisms that can lift air, but some of the most common mechanisms are frontal (cold fronts usually bring the strongest thunderstorms), orographic (mountains, hills and other high-elevation terrain), and convergence boundaries (air collides and has nowhere to go but up).
This transfer of heat from the warm, rising air to the atmosphere (the process known as convection) also brings moisture to upper levels of the troposphere, the layer of the atmosphere where we reside and the weather we know takes place. Here, where the air is cold, the water vapor condenses on particles to form clouds. As the cloud expands, it grows upwards into areas of the atmosphere where temperatures are below freezing.
In the sub-freezing air, liquid water drops begin to cool below the freezing point. Some drops freeze, while some drops become “supercooled,” whereby liquid water remains in the liquid phase despite temperatures being below 32F/0C. The ice particles grow by condensing vapor upon their surface, or by accumulating the supercooled water droplets, which fully freeze upon contact with the ice particles.
The formation of these ice particles is very important for the development of the “thunder” part of these storms. When two ice particles collide in the frozen region of the cloud, the collisions rip off little bits of the particles and an associated electric charge. On a large scale, these collisions end up creating regions of clouds that are positively charged, and some regions that are negatively charged. Wanting to be in a neutral state, the cloud discharges the electricity, creating the brilliant flash of light we call lightning.
This describes the development phase of thunderstorms. The other two phases are the mature stage, where rain begins to fall, and the dissipation stage, where the warm, moist air gets cut off from the storm and rainfall begins to slow, although lightning remains a threat.
Thunderstorms become severe when it has either hail of one inch or greater, wind gusts of 58 miles per hour or more or has produced a tornado. Severe thunderstorms are most common in a swath from Texas to southern Minnesota, but no place in the U.S. is entirely safe from severe thunderstorms. When a severe thunderstorm is forecast for your area, heed any and all official warnings and stay away from flooded roadways. Remember, “Turn Around, Don’t Drown” and “When Thunder Roars, Go Indoors!”
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Story Image via Pixabay