Thunderstorms

Thunderstorm is a rain with thunder and lightening. They are of short duration occurring over a small area. Thunder storms occurs in an area where temperature is high and a strong convective updraft is possible. they are less frequent on water bodies due to low temperature. Thunderstorms occurs in a cloud called Cumulonimbus and can produce snow sleet and hail as well. The damage resulting from thunderstorms is mainly by strong downdrafts of air in the core of it, and lightening produced by it. Strong thunderstorms can also produce tornadoes and waterspouts.

The thunderstorm development cycle can be divided into three parts as follows –

1. Towering cumulus stage – In the initial time ground is heated due to solar insolation and a low pressure area is developed. This low pressure leads to rise the air and surrounding air comes to fill the space, thus a continuous updraft of air causes the formation of cumulus cloud that is high enough to call towering cumulus cloud.
2. Mature stage –
   • The updraft of air leads to decrease temperature as per Dry adiabatic lapse rate, and reaches to the dew point forming the rain drops. The rain drops collides and coalesces gaining wait to come down but again lifted due to continuous buoyance force that is exerted by the uplifting air.
   • These rains come with high speed when becomes too heavy to be held by buoyance force, causing heavy rains.
   • When clouds extend to high where freezing point occurs, hails are formed and comes down as hailstorms along with heavy precipitation.
3. Dissipating stage –
   • This stage is dominated by downdrafts that cuts-off the inflow of thunderstorms, the updraft disappeared and thunderstorm dissipates.
   • In the few minutes, the storm dissipates and clear weather starts to prevail.
   • Downdrafts is more than 4km in diameter and can produce 60-120 km/hr wind speed, which can be very hazardous to the aircrafts.

Types of Thunderstorms :-

1. Single-cell thunderstorm – This term technically applies to a single thunderstorm with one main updraft. Within a cluster of thunderstorms, the term “cell” refers to each separate principal updraft. Thunderstorm cells occasionally form in isolation, as the occurrence of one thunderstorm can develop an outflow boundary that sets up new thunderstorm development. Single-cell thunderstorms normally last 20–30 minutes. Generally they driven by heating on a summer afternoon. In Kerala they are called Mango Showers while in Karnataka they are called as Blossom showers.
2. Multi-cell thunderstorms – This is the most common type of thunderstorm development. Mature thunderstorms are found near the center of the cluster, while dissipating thunderstorms exist on their downwind side.  Individual cells usually last 30 to 60 minutes, while the system as a whole may last for many hours. Multicell storms may produce hail, strong winds, brief tornadoes, and flooding.
3. Squall lines – A squall line is a group of storms arranged in a line, often accompanied by “squalls” of high wind and heavy rain. Squall lines tend to pass quickly and are less prone to produce tornadoes than are supercells. 
4. Super-cell thunderstorm – A supercell 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 like a small cyclone. The tornado is a very small extension of this larger rotation. Most large and violent tornadoes come from supercells.

A mesocyclone is a rotating vortex of air within a supercell thunderstorm that can sometimes produce tornadoes.

Hazardous :-

• Cloud to ground lightening
• Hailstorms
• Tornadoes and watersports
• Flash flood
• downburst
• Thunderstorm asthma