How a tornado starts

A tornado begins with a set of meteorological conditions leading to the formation of a powerful upward flow of air. Here are the main stages of tornado formation.

Conditions for thunderstorm cloud formation

Warm and moist air. The presence of warm and moist air on the surface of the earth, which can condense as it rises to form thunderstorm clouds.

Cold and dry air. A layer of cold and dry air above warm moist air. When warm air rises, it collides with cold air, creating instability.

Formation of a thunderstorm cloud

Convection. Warm moist air rises, cools and condenses to form a cumulonimbus cloud. This process releases the heat of condensation, which enhances the upward flow of air.

Wind Shift. The change in wind speed and direction with height (wind shear) creates rotational movement of air in a thunderstorm cloud.

Mesocyclone formation

  • Mesocyclone. A mesocyclone, a rotating upward flow of air caused by wind shear and temperature differences, forms within a thunderstorm cloud. The mesocyclone is a precursor to tornadoes and is an important component of supercell thunderstorms.
  • Funia clouds. A descending cone forms at the centre of a mesocyclone, which may become visible as a cloud funia (vortex). If this rotating stream reaches the ground, it becomes a tornado.
  • Contact with the ground. When the cloud funia reaches the ground, a tornado is formed. The vortex picks up dust, debris, and moisture, making it visible. Tornadoes are characterised by strong winds that can reach speeds of up to 300 mph (about 480 km/h) and cause significant destruction.

The basic conditions for tornado formation include severe atmospheric instability, the presence of moisture, wind shear, and the presence of upward air currents, which usually occurs in severe thunderstorms, especially supercell thunderstorms.

How long a tornado lasts

The duration of a tornado can vary greatly depending on a variety of factors, including intensity and environmental conditions. Here are the main categories of tornado duration:

Short-term tornadoes:

Many tornadoes last only a few minutes. They can be relatively small and weak in intensity.

Medium-duration tornadoes:

More typical tornado durations range from 5 to 20 minutes. These tornadoes can reach moderate strength and cause significant destruction.

Prolonged tornadoes:

In rare cases, tornadoes can last 30 minutes or longer, sometimes even several hours. These tornadoes are often part of large supercell thunderstorms and can be extremely destructive.

On average, most tornadoes last about 10 minutes, but there are examples of tornadoes that have lasted much longer. For example, one of the longest recorded tornadoes, known as the Tri-State Tornado, raged for about 3.5 hours and passed through three US states in 1925.

It is important to note that the exact duration of a tornado depends on many factors, such as the topography of the area, the presence of moisture and air temperature, and the structure and intensity of the storm system from which it forms.

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