What kind of thunderstorm causes tornadoes

The warm air becomes cooler, which causes moisture, called water vapor, to form small water droplets - a process called condensation. The cooled air drops lower in the atmosphere, warms and rises again. This circuit of rising and falling air is called a convection cell. If this happens a small amount, a cloud will form. If this happens with large amounts of air and moisture, a thunderstorm can form. Thunderstorms can consist of just one convection cell, multiple convection cells, or even one extremely large and powerful convection cell.

Below is a description of three types of thunderstorms, classified by their structure: single-cell, mulit-cell and supercell. Tornadoes can occur at any time of year, but they are more common during a distinct season that begins in early spring for the states along the Gulf of Mexico.

The season follows the jet stream —as it swings farther north, so does tornado activity. May generally has more tornadoes than any other month, but April's twisters are sometimes more violent. Farther north, tornadoes tend to be more common later in summer. Although they can occur at any time of the day or night, most tornadoes form in the late afternoon. By this time the sun has heated the ground and the atmosphere enough to produce thunderstorms. The denser cold air is pushed over the warm air, usually producing thunderstorms.

The warm air rises through the colder air, causing an updraft. The updraft will begin to rotate if winds vary sharply in speed or direction. As the rotating updraft, called a mesocycle, draws in more warm air from the moving thunderstorm, its rotation speed increases. Cool air fed by the jet stream, a strong band of wind in the atmosphere, provides even more energy.

Water droplets from the mesocyclone's moist air form a funnel cloud. The funnel continues to grow and eventually it descends from the cloud. When it touches the ground, it becomes a tornado. Twisters are usually accompanied or preceded by severe thunderstorms and high wlnds. Hail is also common. Once a tornado hits the ground, it may live for as little as a few seconds or as long as three hours.

The average twister is about feet wide and moves about 30 miles an hour. Most don't travel more than six miles before dying out. Massive tornadoes, however—the ones capable of widespread destruction and many deaths—can roar along as fast as miles an hour. These measurements are scientists' best estimations. Anemometers, which measure wind speed, cannot withstand the enormous force of tornadoes to record them. Using units F0 to F5, the Fujita scale measures a tornado's intensity by analyzing the damage the twister has done and then matching that to the wind speeds estimated to produce comparable damage.

The United States now uses the EF Enhanced Fujita scale , which takes more variables into account when assigning wind speeds to a tornado. Every year in the United States, tornadoes do about million dollars in damage and kill about 70 people on average. Extremely high winds tear homes and businesses apart. Winds can also destroy bridges, flip trains, send cars and trucks flying, tear the bark off trees, and suck all the water from a riverbed.

High winds sometimes kill or injure people by rolling them along the ground or dropping them from dangerous heights. But most tornado victims are struck by flying debris—roofing shingles, broken glass, doors, metal rods. The number of average deaths per year in the United States used to be higher before improved forecasting and warning systems were put into place. Meteorologists at the U.

National Weather Service use Doppler radar, satellites, weather balloons, and computer modeling to watch the skies for severe storms and tornadic activity. Doppler radars record wind speeds and identify areas of rotation within thunderstorms.

Since Doppler radar has been in use, the warning time for tornadoes has grown from fewer than five minutes in the s to an average of 13 minutes by the late s. A supercell thunderstorm strikes in South Dakota. Since thunder comes from lightning, all thunderstorms have lightning. 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.