Thunderstorm

Thunderstorm and Tornadoes are strong local storms. They are brief and occur across a tiny region, yet they are violent.Thunderstorm are storms that include thunder and lighting, as well as strong rain or hail. Thunderstorms are more common on the ground, where temperatures are high. Because of the cold, thunderstorms are less common on aquatic bodies.

How does a thunderstorm form?

Cumulus stage

Ground is significantly heated due to solar insolation.
A low pressure starts to establish due to intense upliftment of an air parcel (convention).
Air from the surroundings start to rush in to fill the low pressure.
Intense convection of moist hot air builds up a towering cumulonimbus cloud. [I have explained how condensation occurs in previous post]

Mature stage

Characterized by intense updraft of rising warm air, which causes the clouds to grow bigger and rise to greater height.
Later, downdraft brings down to earth the cool air and rain.
The incoming of thunderstorm is indicated by violent gust of wind. This wind is due to the intense downdraft.
The updraft and downdraft determine the path of the thunderstorm. Most of the time, the path is erratic.

Dissipating stage

When the clouds extend to heights where sub-zero temperature prevails, hails are formed and they come down as hailstorm. Intense precipitation occurs.
In a matter of few minutes, the storm dissipates and clear weather starts to prevail.

Types of Thunderstorms

Convectional, Frontal, Orographic Thunderstorms.
Isolated Thunderstorms, Multiple-Cell Thunderstorms, Supercell thunderstorms.

(1) Thermal thunderstorm

Caused due to intense heating of ground during summer.

(2) Orographic thunderstorm

Forceful upliftment of warm moist air parcel when it passes over a mountain barrier creates cumulonimbus cloud causing heavy precipitation on the windward side.
Orographic ‘Cloud bursts’ are common in Jammu and Kashmir, Cherrapunji and Mawsynram.

(3) Frontal thunderstorm

Thunderstorms occurring along cold fronts.

(4) Single-cell thunderstorm

Single-cell thunderstorms are small, brief, weak storms that grow and die within an hour or so. They are typically driven by heating on a summer afternoon.
Single-cell storms may produce brief heavy rain and lightning (Very common in India during summers, mostly April, May. In Kerala they are called ‘Mango Showers’ and in Karnataka ‘Blossom showers’).

(5) A multi-cell thunderstorm

A multi-cell storm is a thunderstorm in which new updrafts form along the leading edge of rain-cooled air (the gust front).
Individual cells usually last 30 to 60 minutes, while the system as a whole may last for many hours.
Multi-cell storms may produce hail, strong winds, brief tornadoes, and/or flooding.

(6) A super-cell thunderstorm

A super-cell is a long-lived (greater than 1 hour) and highly organized storm feeding off an updraft (a rising current of air) that is tilted and rotating.
Most large and violent tornadoes come from super-cells.

Motion of a thunderstorm

Path of a thunderstorm is erratic. Motion is primarily due to interactions of its updrafts and downdrafts.
The speed of isolated storms is typically about 20 km (12 miles) per hour, but some storms move much faster.
In extreme circumstances, a supercell storm may move 65 to 80 km (about 40 to 50 miles) per hour.

Downbursts

Downdrafts are referred to as macrobursts or microbursts.
Macroburst is more than 4 km in diameter and can produce winds as high as 60 metres per second, or 215 km per hour.
A microburst is smaller in dimension but produces winds as high as 75 metres per second, or 270 km per hour
They are seriously hazardous to aircrafts, especially during takeoffs and landings.