Thunderstorms and tornadoes

Water vapour absorbs energy during evaporation and releases that latent heat when it condenses into cloud droplets or ice. The released heat warms the surrounding air, making it more buoyant. This strengthens upward motion and helps a convective storm become deeper and more energetic.

Hail forms when strong thunderstorm updrafts carry water droplets upward into air below freezing. The droplets freeze and may collect additional layers of ice during repeated upward and downward movement. Stronger updrafts keep hailstones suspended long enough for them to grow.

Wind shear means that wind speed or direction changes with height. This difference can create horizontal rotation in the lower atmosphere. A strong thunderstorm updraft may tilt that rotation into a vertical position and concentrate it, helping a tornado develop when other conditions are favourable.

A gust front is the leading edge of cool, dense air spreading outward from a thunderstorm downdraft. As this outflow moves along the ground, it lifts and displaces warmer air ahead of it. The boundary can bring sudden wind shifts, gusts, pressure changes and sometimes new cloud development.

When raindrops evaporate into relatively dry air below a cloud, they absorb heat from that air. The resulting evaporatively cooled air becomes denser than the surrounding warmer air and accelerates downward. This strengthens the downdraft and may produce a spreading gust front or a sudden, strong wind at the surface.

Rain-cooled air descending from a thunderstorm can spread outward along the ground as a gust front or outflow boundary. At its leading edge, the denser cold air undercuts warm, moist air and forces that air upward. If moisture and instability are sufficient, the lifting may create new clouds or even initiate additional thunderstorms.

Heating at the surface makes the lower air warmer and more buoyant, while cold air aloft increases the temperature difference with height. This steep temperature gradient makes the atmosphere unstable. Warm moist air can then rise vigorously, cool, condense, and form deep convective clouds and thunderstorms.

Water vapour absorbs energy during evaporation and releases that latent heat when it condenses into cloud droplets or ice. In a rising thunderstorm column, this released heat warms the surrounding air, increases buoyancy, and strengthens the updraft. The enhanced updraft supports deeper clouds and more intense storm activity.

The change of wind speed and direction with height is called vertical wind shear. It can create horizontal rotation in the atmosphere, which a strong thunderstorm updraft may tilt and convert into a vertically rotating circulation. In a suitable supercell environment, this organized rotation can support tornado formation.

A cumulonimbus cloud can rise until it reaches the stable layer near the tropopause, where the surrounding air strongly limits further vertical growth. The cloud then spreads sideways, producing the characteristic flat, broad anvil top. This shape is therefore associated with the upper stable boundary of the troposphere.

Rain-cooled air descends in the downdraft and spreads outward when it reaches the ground. The leading edge of this spreading outflow is called a gust front. It may produce a sudden wind shift, strong gusts, pressure changes, and sometimes a boundary that helps initiate new convection nearby.

During the mature stage, warm moist air continues to rise through the storm while precipitation and evaporative cooling create denser air that descends. These two currents operate simultaneously in different parts of the cloud. Their coexistence produces the strongest rainfall, lightning, turbulence, gusts, and other severe weather.

Moisture supplies water vapour, but moisture alone cannot produce a thunderstorm. Stable air resists displacement: a lifted parcel becomes relatively cooler or less buoyant and returns downward instead of rising freely. Without sustained vertical lifting and instability, condensation remains limited and deep convective clouds are unlikely to develop.

A tornado is a comparatively narrow, violently rotating column or vortex whose damage track is usually confined to a small area, although damage can be extreme. A general cyclone is a much larger low-pressure circulation affecting a broad region and often lasting for days. Thus, their scale and duration are very different.

The cumulus stage is the developing stage of a thunderstorm. Warm, moist air rises strongly, cools, and condenses, so the cloud grows vertically. Updrafts dominate and precipitation has not yet produced a widespread downdraft. Continued uplift may carry the cloud toward the mature stage, when updrafts and downdrafts coexist.

A thunderstorm needs a continuing supply of warm, moist air to maintain buoyant updrafts and release latent heat. If rain-cooled downdraft air spreads across the surface and blocks that inflow, the updraft is cut off. The storm then loses its energy source and enters the weakening or dissipating stage.

A strong updraft keeps water droplets and small ice particles suspended and carries them repeatedly into the very cold upper parts of the cloud. There they freeze and collect additional layers of water and ice during collisions. When the growing hailstone becomes too heavy for the updraft, it falls to the ground as hail.

Lightning produces both a bright flash and a powerful sound wave called thunder at nearly the same event. Light travels through air at about 300,000 kilometres per second, whereas sound travels at roughly 343 metres per second under ordinary conditions. Therefore, the flash reaches an observer much earlier than the sound.

A tornado concentrates extremely strong rotating winds into a relatively narrow track. The pressure difference, suction-like effects, flying debris, and intense wind force can destroy structures within that track, while nearby places may receive much less damage. This sharp contrast explains why tornado damage is highly localised.

A microburst is a concentrated downdraft that descends rapidly from a thunderstorm and spreads outward after reaching the surface. Its winds are usually straight-line outflow winds rather than a rotating column. A tornado, in contrast, is a rotating vortex extending from a severe storm toward the ground, and both phenomena can cause serious damage.

Flash flooding occurs when intense rainfall arrives faster than soil, drains, streams, and urban channels can absorb or carry it away. Thunderstorms can release a large amount of water in a short period, especially over impermeable surfaces, steep slopes, or already saturated ground. The rapid excess of water causes sudden flooding.

The updraft carries warm, moist air upward and supplies the buoyancy and moisture needed for continued cloud growth. If it weakens, less vapour reaches the cold upper cloud, condensation and latent-heat release decline, and the cloud cannot build vertically as effectively. Storm energy, precipitation intensity, and severe-weather potential then decrease.

A funnel cloud is a rotating, funnel-shaped extension beneath a strong convective cloud. It is generally called a tornado when the rotating circulation makes contact with the ground, although the visible funnel may not always extend all the way down. Ground contact is therefore the key observation supporting identification of a tornado.

Some falling precipitation evaporates into comparatively dry air beneath or around a storm. Evaporation absorbs heat, cooling the surrounding air. Cooler air becomes denser and negatively buoyant, so it descends more strongly. When it reaches the surface, it can spread outward and produce powerful gusts or a microburst.

Very severe thunderstorms contain strong updrafts, downdrafts, hail, lightning, heavy precipitation, and rapidly changing wind conditions. The contrasting vertical currents can create severe turbulence and sudden altitude changes, while hail and lightning may damage an aircraft. For this reason, aircraft generally avoid the core of such storms rather than attempting to fly through it.